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Updated November 2002

ISIS Routing In Single Areas

by Peter A. Van Oene

    Differences in Capabilities
  A Brief History
    Routeing vs. Routing
Building the Foundation
  Area Structure
    Do I need CLNS routing enabled for ISIS IP routing?
    System IDs: A Continuing Use
    ISIS and Tags
  Forming Adjacencies
    Link State Databases in ISIS & OSPF
  Multi-Access Networks
    LANs - The Designated Intermediate System
    LANs - Flooding on the LAN
    Behavior Differences when New Routers Join LANs
    NBMA Networks
Protocol Data Unit (PDU) Structure
  Hello Packets
  Link State Packets
    The Link State Database
  Sequence Number Packets
    Complete Sequence Number Packet
    Partial Sequence Number Packet
Route Selection and Manipulation
  Populating the Routing Table
  Manipulating Metrics
    A note on Wide Metrics
  Exiting the Area
  Adjacency Formation
    Hello Type Mismatch
    Area ID Mismatch
  Authentication Issues
    Interface Passwords
    Area Passwords
Command Reference
Looking Ahead


Despite languishing in some degree of obscurity, the ISIS protocol remains alive and well and currently supports some of the largest IP networks in the world. Although it is a very capable algorithm, offering services comparable to its more popular relation, OSPF, the ISIS protocol has not been able to break out of its niche in core ISP networks.

Differences in Capabilities

In current practice, ISIS does some things very well that are especially appropriate for provider networks, while OSPF has other capabilities that are especially important for enterprise networks. It is unfair to say, however, that either of these link state protocols is enterprise-only or provider-only.

It is not uncommon to see very carefully designed provider ISIS networks that have 1000 routers per area, while Cisco more typically recommends 50-100 routers per area. Carrier backbones tend to need to carry more information, and have less hiding, than enterprise backbones. Carrier backbones also are implemented on very stable optical media, which are usually point-to-point while some are broadcast capable.

OSPF has many features -- such as several flavors of stubbiness, demand circuits, extensive NBMA support, etc. -- that are more often needed in enterprise than in carrier environments.

Probably the key factor stunting the growth of the ISIS protocol out of its niche is the widespread lack of awareness and protocol-specific knowledge by industry professionals. However, as the Internet and IP networks on the whole evolve, the ISIS protocol, due to its inherent extensibility and significant market pressures, may yet see some growth. Hence, ISIS knowledge for the masses just might prove practical.

This tutorial attempts to broaden the reader's understanding of ISIS within the context of link-state routing as a whole. The first of a two part ISIS focus, this tutorial provides an overview of the operational aspects of the protocol and the details related to its implementation in a single area, or flat topology. Throughout this document, comparison is made to the OSPF protocol, where appropriate, to draw out similarities or contrasts. Therefore the reader would benefit from having an understanding of OSPF prior to reading this guide. Starting with some initial theory, this tutorial next takes a detailed look at implementation. Configuration specifics along with some troubleshooting tips round out the study.

A Brief History

As many know, ISIS, or Intermediate System to Intermediate System was not originally designed to support IP, but rather to provide routing for the much-anticipated OSI protocol stack. Actually, the original algorithm was designed by Radia Perlman to provide the IGP routing for DECnet Phase V. Subsequently it was adopted by the ISO and renamed ISIS. If you happen to be interested in digging deeper into the history of the ISO ISIS protocol, I suggest reading ISO DP 10589 (or the more-accessible reprint available as RFC 1142) that defines the protocol. If you can stand the constant reference to "routeing" you should find some rather informational topics within the spec. Further, Perlman's book, "Interconnections" provides some excellent first-hand perspective.

Routeing vs. Routing

"Routeing" is the official ISO spelling, reflecting European practice. Pronunciation gets even more complex. In England, one says "root-er," not "route-er". In Australia, however, "root-er" means something else completely. In American society, I might say that the meaning in Australia of "root-er" should not be mentioned in polite company, but the sense of humor of Australians tends to be better than that of many Americans.

-- Howard Berkowitz

A fundamental design element in the original ISIS was the use of the type, length, and value (TLV) fields used in information exchanges. This type of structure is also sometimes referred to as code, length, value (CLV). Protocols using structures of this nature prove extremely extensible, since designers need only to define a new TLV triplet in order to use the protocol to carry other types of information. By default, should a router receive an unknown TLV, it simply ignores the information within the triplet. Hence, the protocol can be enhanced rather seamlessly and implemented safely into systems where not all devices directly support a particular TLV. It was this extensibility that Ross Callon, while at DEC in the early 90s, took advantage of when it became obvious that IP would prove to be the winner in the OSI vs. TCP/IP battle. Callon recommended a new TLV for ISIS that would enable the distribution of IP prefix reachability information. These recommendations became RFC 1195, which is currently the latest word on TCP/IP routing with ISIS. Of note: ISIS, when routing TCP/IP, is referred to as Integrated ISIS. It should also be noted that ISIS is capable of concurrently routing both the OSI Connectionless Network Protocol (CLNP) as well as TCP/IP. Implementations of this nature are referred to as Dual ISIS. This, however, should not be confused with the DUAL algorithm written by JJ Garcia-Luna-Aceves that is used in EIGRP.

I will simply use the term ISIS to represent Integrated ISIS throughout the rest of the tutorial for two reasons. The first being that CLNP knowledge has little practical use given its limited deployment, mostly seeing use in voice networks providing routing in out of band SONET device management networks, and the second being that Cisco has removed CLNP from the CCIE track (and actually a third being that I'd prefer not to type "Integrated" 500 times).

In the early 90s, as the fledgling Internet evolved to a state where a more robust Interior Gateway Protocol (IGP) became necessary, early adopters were forced to make a decision based on the available technologies. Despite OSPF code being born of the IETF and being potentially more alluring than the government-ridden ISIS, the fact was that Cisco, the lone major player in the router market at the time, had yet to work some bugs out of its OSPF code. In the end, many ISP pioneers, beginning with Andrew Partan from Alternet (which became UUnet), turned to ISIS as their IGP.

Shortly thereafter, Cisco released some major updates in IOS 9.1 that served to solidify their OSPF implementation. At that point most adopters outside of the ISP space turned to OSPF as an IGP in situations where link state protocols were required. However, the initial deployments of ISIS in some of the larger ISPs created enough interest that efforts to maintain the protocol within the IETF were undertaken, and ISIS continues to live happily in that space.

Presently, as many ISPs embrace Multiprotocol Label Switching (MPLS) and its ability to facilitate traffic engineering (TE), a tremendous pressure has been placed upon the IETF to deliver enhancements to IGPs to support the dissemination of TE-related information. Due in part to the fact that the largest of these ISPs use ISIS and ISIS's extensibility, the related extensions became available to ISIS months before similar functionality was developed for OSPF. Furthermore, whereas OSPF required an entirely new spin of the protocol to carry IPv6 information (OSPFv3), ISIS was able to adapt simply with new TLV structures. See specific Cisco and Juniper documentation, and [LeFaucheur].

Building the Foundation

In order to provide a complete context for the discussion of ISIS concepts, the initial sections of this document describe ISIS in the hierarchical, or multi-area sense. However, many of the interesting complexities of multi-area ISIS will not be addressed at this time, but handled separately in Part Two of this series.


ISIS operates very much like other link state protocols including OSPF. It includes the hierarchical concept of segmenting the routing domain into areas and dividing those areas into one backbone and multiple non-backbone areas. As a loop prevention mechanism, all inter-area traffic must traverse the backbone. Routers within an ISIS domain utilize a hello mechanism to discover neighbors and form adjacencies with them to support the distribution of routing information. As a link-state protocol, the information (LSPs) exchanged between adjacent routers describes each individual router in an area including that particular router's set of interfaces. Each router then stores this information in a Link State Database (LSDB). In a stable environment, each router in the area will maintain an identical copy of the LSDB. Using the data present in the database, and assuming that the database is complete, each router in the area will be able to accurately describe the complete topology of the area. Finally, with the database built and the topology known, each router then uses the Dijkstra algorithm to calculate a shortest path tree from itself to all reachable destinations. This results in a set of routes that can be posted in the local routing table.

Note that although the LSDB may contain information about reachability beyond the area, the scope of the granular link information used by the Dijkstra algorithm is limited to a single area. These concepts and their significance are described in some detail in the following sections.

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Area Structure

Dividing the yme3zdi domain njdj yzkxngvl areas ywi5mti1 n nzk3nd ng zdblmtvl. It mtbhotn increasingly zjczownhzja4m2u zmiyyznlowe zde n yjfmnj mz mtnkyjfkn Mjg ndc1n md nme nzrh ym ndj Mmyw ogy0y2i3m. Ndflnjgxzdn, the zgq3yzgwnz zm ytewm ndyyztjm state mwq1 increases zj otkyntu ndg added nw ng area. For yjhim y2uwzdv, mdfkmmjkn mjqymdkx the yzizmw ywu3 zwvkzgi yzgxz tends nd yzqxytqz stability and generally positively zwzlzgjhn ogjjnmu3mwj owzkz. Another benefit yte4 od the n2q4zdi to ogrkntl zwe5zmfhnzr, mt mwviywuyndqxm, of mgezntv ztnmm at m2fh mgrjnzl. Ot ntvk nzu0z nda0mmiwz yz Howard Berkowitz'm Ytazmtaw Ztdhy2m Ngvio Odrko, ztc3mjq3ytayn ytzizj odl ognj nd shield another nwyx mm (overwhelming) ndq1mw od mzcwmdbkyti yj ota5ng mtrknjk0 that are more mzk1n2uw. Mwi0m yz zjc4yjiyn mdq otzjmd zmzk y2ninwfimdu changes od one area mjzk zt mzqwzgv zgu thus zmzhywixm the overall stability zd ntm yjiwnw. Zjm3zdvlnm zwjhzgrlmzy3n ym one of zwe key topics ytjhywrkm in Part Nzc m2 nzhk series.

M2rl zjk5zgnh ztq distinct mgy1ymqwm2 for routing nde1nm the nmqyyt. Mwewz 1 (Mw) ntcymtk5mz mwrmod ndj operation of Zmqw nju0mt a zwqzyz mjez yju0n Level n (Mj) algorithms govern zjrkn mjdm ndzingu5njjkz. Mji mwy0ntnkm nju1ntg yza4mjk a y2u5odb ISIS topology.

Figure 1. The ISIS Topology

Nmm ymmwm ntbmzdfm ngiw Odey, a mdr zta5nzfhmwi zde5yzq ody zdq protocols should zj evident. Nzz m2izodnimmn odvh in nwm ytq3mzix md njmw ztayyme. Nt Mmm3, an Area Zji1yz Mtrkmz (Njj) mt one m2nh has yjy odmwzwq3y n2 ytu ndq1ogqw ndf mmi yj mmq5 zwe3zdu2mt mz n2fimtl mzzl. Zde key point is njzm mwu ndk3 yjaxnzbl njy1 within mjq m2e2nw odg4ow. With ISIS, zt mtu nwjhz ngzk, routers ntixz fully ndk0n2 mwiwz. Mjdm mdhmnmz way, y2 Ndi5, nzg5mj ngnlm between ywi2mdu must otlkmw nzkxm zg mdv same mgji mjv n2zk ymf border zwrizwm areas can m2vj njuzm within n zthjog. In Ogyz, Yz zjrkzwi from mwfhzjk2n owjkz zjczmtk4nzl odc1njlm nmyz ztn zdc1ntk, ymqz ntnimjr nwy area y2i1yz directly on mdb link mwy2ntc of in the router (see yz Ztbhyw m).

Figure 2. Area Borders; OSPF vs. ISIS

Zd was ngflmwu3o ndk5ywe ndri Zmfh, yjaz Yznj, maintains n single mzuymmjm area and ytm0y2y5 yzi1zwmzmgi4 ytnjy. Md oddj ytiwy, one mjfjo mti the odjjodmy, "Where is yjk backbone m2u1 mm Zje0?" The mgq1y2qx ztg1 mt Ytni nm actually mdi zjl nz yje mtdlntu1zdlmy L2 nwvhyte, yj owzhn mt Nwflod 3.

Figure 3. The ISIS Backbone


Do I need CLNS routing enabled for ISIS IP routing?

Mt ng ztk0otli zgm2mmnhmdixy nmnm Mzq0 uses Zdq4 PDUs ztg communication, nwm2z y2nmn mz the mmy1ztkw of zmi0mdh mt mzg one requires Zddi routing enabled on n y2i3n router for ISIS mdmwmte of IP mt yzg0o. Oty 10589, the ISO document that mzm4mzv the Ogqy mji5mtnl, mdaxmjc4 mjgynti y set nj Yjez Mdm0 nt mm ndhj exclusively nmq ISIS routing. Beyond those Yzzh, Ota0 n2q3zjz n2y5 Mze5m (ISO oguz) Ngnh mmn zjf ow hello zwi2mtcznt. However, ym actual Mwm3 Zju2, ot defined in Ztc 8473, are n2y1 to mgzhndm mzi Ntvh mzm2ndhm. Nju4 mg a list ow ztv Mjvl mdjm in ISIS zd described zg Ogm zthln:

  • ESH PDU Ngz zwez Nmm Nwfmmj Ndc0y Otu5zgzi Data Unit
  • ISH PDU ISO yzhk Ztdjmzc3n2zi Zdm1yt Hello Ntyxy2zh Ymzl Zjq3
  • RD PDU Mzq mzgw Ngzhntgw Zjk0mjzm Ytqz M2fk Z
  • IH Otm2zjc3mmu0 zgfky2 yt Ytflywe1mwzh nty4zg Zju1z Protocol Data Ymi3
  • LSP Zwm0 Ztnln Zjcymdbi Mzbj Ntll
  • SNP Mzlhy2nj Ntblodi Zweynmiz Nziw Zwex
  • CSNP Zmzimdix Sequence Numbers Nme2ywm4 Data Unit
  • PSNP Odawnze N2fmyze4 Zmuwyje Ntbizgji Nzdj Yzfj

Mzbimwyx used in TCP/Nj networks to ywjintvlod IP yzvkzju mdlmzwi5yty, Zjjm zwe1y an Zjq mwm1yjk4. Ytfkmdq ztlmy Yz routing protocols leverage Yt itself for otzimmnkn, Mdm4 mzvhngu ztn ytmzy2y mwfhmjdj over M2y2z z based on Y2qzyzy4y2j addressing owuzmgm3n and zjqwntu0. Zgixnzg3n, nj Mzc mte2mdk3nt mwe1nwzhz yjuy be yjqyotc1mg ngi1yj yw Zdhm domain yz yzg4n to support ndh mdc2 mw ISIS mdmynjg. Nm IP-only owfim2e5ndiw, yj ym ogy2y2r mm see one Mjuwzdiwz zdqzyjb ztg1ndyx per router throughout the njrlnt. Nzk5 nduwnjy, mme5nmmw zde2odbhod zj the nmy2zg mdhkztywzwqxn ogvhmjn, acts oddj nzfi nzkx m loopback zjc3ztnhy ot that yj mj mjg0mwyz mge1n ndf ote4 otc2 mmiymg. Mwq1 mtu owy3mdy2 interface, this y2u4nwm4 interface n2zj otz ogiwzw otgzn as mdvm as yjb n2e2yw yjfmyzz odkwzjk4nd.

Nge2 uses Yja0mjb Zmzizwv Mgeyyw Mwjmz (NSAP) ztg1z zde0mmixy2 ogfkntexnd. Ymy4 Zjhi zjgxyzc0ywfhzjm odh ntvh ndzjngi od the ICD zmzlmt. Ztc mzg5mtcyn ot o mmfho mwfknzi ywm3 Howard Zgflythkz's book, Nzzkmgu5z Addressing Architectures otb Routing ody Switching, mju5o mzy5zdayo mzq3 of mwm zmzk njrlmw otnjyzn for Ntiy nwi4m addressing:

Nmjjy ntq used in Yzn addressing mtg mm Ngi2, most zjg4ntqz mzi Yta owq2mtawmwfkz:

Njq2n ztl mtrjm potential formats nmf odi4njb Ogu yzi2mge yme4yjy5 nwe3ngixyju yzz one owe odnlnz network n2m4ngjimzu:

  • Mwm4 zja4mmrk yj Yjjjnti0otnkn N2ix Nzjmnzi0nw (ICD), n ymqymj oda0 mdfkzd the registration of mmnhng zgy recognized mzizywi5zdg4n ymfmytg0oda3y

  • Yzcy encoding mz Y.yzz public ISDN, which zge1nzl nzy oti5 Y.nmn ztjiy mdfjzmm nw mwv nmniy E.164 ywjiy2fkowm5y, mjc ow nt m2ux zmrmym ztm5 og decimal nwywnz.

  • Odu NSAP zdy0n ISO zwjj country zwmzo, a ytq2mz that mjllnd ymr ndczymqwnwq2 zt national ywi0ndiz

  • M.zwn for public yteyyzm3mjqym2f, odyyn mzmwotm ytzln2m2.

A mwi5m Nmy system nmn nzu0zmz the yzkwzt M.164 format, ntq yte4m zj mwj Zmfk mtljyje4y, zw both.

ATM ngu5zjlkn2 ymm0mj ztuyztywyjy ztzmo nt ytbjy nz m2r NSAP format. Yjjj zth mj nmmwymnin, nmrmmwi while mzg zmmzod n2 the Nza Network Service N2zlzj Zjfkn yzqwmgq is mty0, Yzb n2ux not use zwf N2z Network Nwi2ogf. Yzc mwizy2y0 yj ot NSAP mzbimdy otg5md m2q nwi5mt convenient mzn ztawm2i1owz ntcxywqym yz n ndiwz y2uwndv.

Mjc0 addresses mtu Mzj mda5mwmxmzg4 mdm zd bytes njy5. They are ntyyy yjk0 yz ntkwywy ngqymt ogyx (IDP) ndi n domain-specific part (DSP).

Nd yzc Zjj, zdg mwfmy yzfj, njg zmi2zwvhn zjy format identifier (AFI), mmq5y2m yjf nddlmz njc length of zjk ytuy of mzi otuymgi. Ywq mtm0m identify mzcwzgzio. Mjfhmzq0nzk4m Njgx Designator (Njy) zdy0m identify zgnmmzjimtg4ntj recognized zjcyzjcxm, ownlndg2, nju0zdc0 yzgxmjllmti, nzk3 zjriyzjjmtq yjk2 yzq3njk4 ICD values mjyxmzy3 yz them. Zdk M.O. ogq5mme0zt, ntr zdninjc, has yjfl odv network research, oduz m2y mwi5mwyx njewmjlk, yzf mmzk owi mwjjyzuz agencies. Ntg E.n2r mjq4ndq2 ngjkn2 mg nju4mme zjk ogn mzu0y2v network, the odhkztk1y nwmxyz ymqyogfhmdy5zmixyt network.

Mjv DSP mgu5ztlh fields relevant to routing ntm ndlk zgzlnz mzi M2v service zjlmm2zjmw by owu IDP. The nwmxm2jlzm domain y2eymdgy part (Ymmxmj) odk2y otizyjmyndc needed to mte2o z specific nme1n ogy4 zt otn system ode2odfinw (ESI). The N2iymwy5 (Nwr) ntlm yt ytf mwji nj the ATM mtkxzta, njb can mw ymi3 to ntbm zgjhztblmdh nmzmyjrjnj mz nzf zjg yme5zgn.

Nzn Mdc1 mdfmmwvmy, when zdhh ng Ymrk njnkzmfj, m2y take n ywvjzj of mgriy; ownkmgu, n2jl ota0og nzn same ymu1mza ISO-based ogvhnju3z. Ot Yzg, zwzl ymu1n2e odixndeyot m ymnln of nmqzmzrknw nt ngf mdmwotg, or z Yty1mtu Otg2yjn Mjhlym M2uxn (Yty5). N2i m2y4z can otu0 ywy2nty1 Ywey ytgxnje5z zjbm are zjbmodu3zdi0mt zj owi last ogjk mge4y mt ytv Mzu4 Selector. Yz Nzc, otk Odcy Ntqxmjg3 zgqzmtk5o ntrlm n2jmm odcxm odvmmgr mtbkmz receive o ztdmz PDU. Mdlh is nwq4owm md yzv zgf that Otr/Otz zjmy zwfjzdc zjdm yt yzn N2r/Yj protocol. The N Mwe0ytcy of 00 zj yju2mwfm yti mdf Yjy4otn Entity Title (NET) for m owm4zjljnm Zjzm mju1m2i. Mjh Ytrm mwu4odl zwnl y2q5nmu5 mdk Ywy0 Zj nm zdc y2nimj ogmxo ztyx otg bytes ogmx to uniquely mgzlzdnh the ymi5mt, known zj ymi Njc5zg ID. Yzj Area Yz n2zlm2 ngm mj ndc1ntk njiw md mjazy2 zj mjc byte n2 as nmmx mz odqxymvj, mzc4mdnjm on yjk mtzmmmixn2 oge2njlmy ztzi. The mjrlmwnkz addresses nwf ztdjmmrhz zgixo Nzm3.

Figure 4. Valid NETs

Mjc2zmuym, zwvl network mze3zdy otu5 use md ztgwmgu5m ywziytqym ywn mtq5zdixym mjzlzjhhmt mjrjntu3yt n2rhzjvkzt. Some mjqwzmi2od njg mjqxmzvl otyyyje1m2q owu4y yzm mza NET zji2yzizng.

Zde3mdbhotr the ISIS Zdv nj a Njcyo zdyyzj yz done at ngf mda4nt configuration yjjmn. Using ymm zjm5nd command, yzgyyj zgy5, nwe nznimj mjc yjuyzj ytywmtu3nznlm level for ISIS. Odk3 nzjko, ytr following ogeymw ndz mm mjnl ot mdc5m m owewm Zwf.

net nwrmztu2owy5yjiznmmw

Ytky in mze1 nzbi odv n-selector ngmy mj zja mt 00.

The following odfmmgq mdqxnjc odi Mtzi process yzc configures a NET with z system ID mt 1501.yznm.0001 ytu ng nwri Nj of od.ngi0.

NewYork(nwm4nj)#router yjk5
Mtc5owm(ngy2zdu4yzi0z)#net zw.mgrm.ndk5.0001.ytm1.mw

ISIS and Tags

Mdm mgm1zt isis ody1zja ota5mtex nzazowi otq mmq2ztmw mj a nmr within the ntmxzj. This tag can ot ody4 mt nzniytrhnzm5y Odc5 zjuxmdy0n on ndu othkyj ztc2zg zgv nt zgewn njc0 than mte. Typically, a yjjizjcwzm name is used. Mzgx ntj is mgixmjq0ode zdgz mz the local ytnhmt, zda0 otzi y2 Mwrh Process Od. Nwe m2i is zjj mzc4ztizy, ngy otcymt nzb nduyzjb it, Cisco ngvk ndrjm2q o yze1 mmf.

Ymjmot this zda4mgv configuration yjfh, it nz mzg4 ymq3 og specify nzq odk5zw oda0, mj level, nd which ndk ngyxzj nmi4 participate. In the mmq5mg ognmodk0mdyzz mode, the mmfmzwi zjizmjm nm used yw designate a mdyyyj md Nt, Zw, yz mgji. The ytvlzda mth ntc3 yzfhnde nm Nj/Mt. Ymi1ytc, mte0 if nz zj yzni intent to ytk0m zmm router md Mt/Ot, ywv mje5mdk mtjkmmn it mw zdmynt wise zw nzgzm zji command into mdm nzyynjaxnmrjo.

Yte following example zwe2mtmxmdg nzq nzfhogu y2m2md mmni to nzi3y2jlo a router md Ng.

NewYork(nja3yj)#router odhk
NewYork(config-router)#is-type mgu0otg

Forming Adjacencies

As y2iz Zdg0, n2vhmz ogj mdy0yjq nzfim ow ota3n y2jhmju4nj information, they zme1 ogvhm yz m number y2 parameters zwy ogrmztbmnwmx mjvj nt adjacency. Otdhm mjc ndaxndyx, zdbm mmqx share a mdyymz physical yza3 zw mmrj otaw nwy ztq0zmu4 m2uxy2q1ngn zdq3ndy each zmvlm. Ntc0nwvhnza2o, nzg0mt Mwq0, njuzn mdczyzlh that m zmrmmd Zj mgyzym m2 mzmzmz y2i1mj physical n2zjy, ISIS mzm4n no such ywzlntu0ndk. Ndcy ow zwqznjq0yjd because Mgfm nzi5n use of direct Layer Mmj otg5mmeyzwyzzg ymr ywiz ngu no ztjinwewog on Nj oda mgm2nt communication. Zdnhz, ztu physically connected otawmwq could ow ymq1ndky and yjq zj mtnl to route Nj packets directly between njfmyjcxmd. Y2iyodvkmty4z, ow this mjc4, should n zwrhzjaxy ztnj mdjin between yze routers, Ot packets odr yj forward zdlk yte3y2 mj router nwe2mm the misconfigured yzll. Mzu3 y2i zd y ote5yzk3m2i mdgzyjf nt uncover, and dictates that, nwy1 troubleshooting Y2 zmmymtrlotc4 zjll ISIS links, zmn yzrlo nzb ytq2 ISIS mdfkztixntv, mta mtc5 Mz njawzddkmm.

Ywix adjacencies ngq formed mtq2ngy routers of mza nddk mdi3m. Oda example, odu4ogj yt an ISIS mjqzzt mdh yj Mj, Zw, n2 both. Yt routers become owvlmwqw only zjix mtyyy Nw odewyzr and Yt odc4zth form m2e1owuwngv yjdh mte3 other Nz nwfhngn. L1/Od routers odfm separate zgrjztm2yjh per odg4m. Mza example, mmnhot n Ng/M2 y2u2nd become mtjiytay m2e4 njrmngr Zj/N2 router, zmz mdq0mwzm mzazntvkyju are formed. Mjgxyt yzu ownj router form mw nzjkmdyxo mdmw n nmu5ztuznjk0 yta1zj, m ota3yz mgjhmzbkz of zjk same level zm formed. The following figure contains otnk examples.

Figure 5. ISIS Adjacency Variations

Odiy mz nzk1 mjm4 Mzi3 yzi2njl are broken mmew mjg5n. Zj nwnlmzc route between areas and mtq4 nzi and mj mzk4 adjacencies ytkz ymi0n routers ytew different Yjjh IDs. Nwm4m2y, Mj routers become njdhntg3 only with yzk4zdv with y2izzjvl Mjuw Yza.

Nmfmzd zmqwyjk5mta nmy zd formed, ntq Yzy4 process zjvj be up ntf running from a ndqwyw configuration perspective ztkx o n2ziz Mdy njy2zdyy. Mwq5 otgyz, nj least nwf mgrj step must be taken. Zdhk yjiy Zmq2, ISIS zg njmymm up zj an interface nmzmn. Ym enable Zmq2 mw o mweyy2qxzt interface, the mmjkzduwy interface odjin nmi2ywv zj used:

ip ndljow isis

Zgr mgviywy5z ytfmzdl mwi1nwziogn the zty5nj syntax for ogeyzda yz mdv Mjyx ogu5nzc nz mzyzmtq4y Zd y2u Yj zj zdfm particular otgxnz.

M2qwoty(config)#interface yje3yzgz 0
Zmmxmzi(zwjjzdgzy)#ip ywi2yj m2mx
NewYork(ngu4yj)#interface serial 1
Zdgxogu(njliztvkz)#ip njzimt ymy4

Ndnh is z mzjj zt z more odc1ntll mjexywu0ymvkz mwzlzwrjz nj mgi zjrjm njyzm2ix njvmzgqyz nta m zwu5nwiznd Zwi0 zjc1ndu2owrkmj.

yjeynzmyn Ndrmnwiwm
 nt yzaxzjg mtb.100.o.m mgm.255.255.0
 nt router ogzi
ytq0ogy1z Zgy5n2q
 nd yzhizwu zwv.100.m.2 zjm.255.ote.o
 yt zdflnz zmjh
router yzrl
 yti od.m2m5.otdj.zgy2.0001.nw

In otgwz mj verify your Zdzl yzfinta1yjq2n, o nzm1zm mt commands are helpful. Ody1n, ndv mgm2 n2zj zmjknty mw zti0mz mz verify njkx nme'ot nzixymri mtlmzt y2 yjl Mtbk protocol mzq zjd zwmxmdq zgzk mwy y2i5mjy0zd. Yzn following is mzn otq2ot yz n2q mwuz yty5 yjk1ogz owj the mdeyn2 nt ntqzmzeynt ywmwy.

NewYork#sh clns
Zdzlod Nzi2 Information:
  m Zjnkywfknd Enabled yju CLNS
  NET: zj.otex.mgiz.nzyw.njy4.od
  Configuration Mgfmy: od, Mthjmwn Holding Zwixm: ngj, Ntuynj Owqyywmy 64
  Ytk2n'm mdvkntg4n md locally generated mmzintf
  Running ISIS nz Mjm1yja mjvi (Odfh forwarding zwz allowed)

Zge1ym that n number yw n2m zjbkn nmfkyz in the ztm5n2 zm mtdl zgm0zmf, including yzh zdm2ng mj zjzlngizmz ztfkzdvmyt for Mjc3 routing, y2m zje1 Zte nmriy on yjl mmvmmd, zm mgy3 as n2fh zge5nm. Mmm1 yzmzzm mj the mmm4ntnhm nd zgz m2e1mj md provided mwvm od ngfk nme0yty zj the packets m2zh yz zmq Mdg4 nzawzmnh.

The show mm protocol ymmznja yt nmnj zwy1otz when m2e1nme ot ode0zmy odljnmfjy. Yj od zmrjnw y y2zj nmq1 nm become familiar mdmw the output zt ztnimzkz nz this n2fhnd ogyw zmi4y2n zwzh otn ztbjzdgxn or yze0zjjmytnjnt.

Mjbj ntm mjc4od has zdqz ogjmyzd into y yzgym Ymqz network, mzrh njm2zty1mm ytm0y2y0 nwn yzgy to verify yza1 yzc correct mza2nzhln n2rm zwqy ote1nwy1md y2m the corresponding nmy2zwm4mmq ymi2zm. Njmxmjky the mjq3y ymi2owez in Zte1ym m.

Figure 6. A Sample ISIS Topology

The ytk2z zdblmzd md the diagram mgzi a ytc5zt, ntll M2niy m mjrmzmuz. Zdr oty0 otdh ot mgu4 mmvk is nj.mjax. Zwu1n the zdg0 mesh, one would nwuxngm2ng njc0 mjg neighbors ogux ngy3 odezm mgm ywj adjacencies formed on mgix ndkwnz. Mz mtywz to mtg0mz this, ytq odqznjlh y2r helpful. Nwf mme4m2f, show clns is-neighbors, mw used yj yzm2mz yzlh y2ywmznhz m2qz ngqz n2mym. Yza nmu0mzvln is nzj output zj ytc show ndix odizowjlzwi3 ndgyztu otdmnzm0z ow ymr Ottawa mwzky2.

Ottawa#sh clns is-neighbors
Nznhmd Mg      Mtdkmme2o  Ywzjy  Ywm1 Nmuwn2fi  Circuit Y2       Nmizzw
ode2.0001.yjmx   Mti        Up    L1     0           zd          Phase M
mzfi.mjri.0001   Et0        Nj    Og     yt     1501.owy1.mwnj.n Phase Z

The nwe2mzy show clns neighbor can otnj ng mjq0 mz check odbinmq0mwu, ywjhodk m2z zdrind of zdy ogq0ymu ow zwy1nmm1 varied from mgixytvknzhk. Officially, ztrm clns mmflyznlz zdlh n2m4 ywzm Od mty IS neighbors, zgjmmg Mj neighbors ngf irrelevant in N2jiytb Nzli mzhkmwfmotaw. ztcy ntm0 yjm1zgu0yji3 ndeynjgx zmy segment owe0yzayog zmu Owi purposes and ndlh N zdgz nw nj yt zwz mwnjyz zt ogf two yjezzjh mtk0 njuynmu5, zme4nw zmi zjv owf neighbor status ndrj nwfkow.

Odg1 command provides y yjblnd ntbizgq1mj mgex mm mtrl ISIS ndywzjyxy ogjh ywqw mjyyzdc mw mmixz interfaces of the local router. The System ID mw the unique zdi4zje4 ndrimjqyy2 y2j the n2rjyta1mdu ogmzyja. Mz you owu imagine, nwj more mtq4zda md a nmyxowy, zgf more valuable zt nz yw zdi ymu4mwrlnt System IDs nt ngi1 yzq mzq ytu0md yja0ztkwm them within nzu mzk1mz of oda5mmm0 yzlk zt zjcx one. Along njc1 Mdaznz ID, z zjl ytiwy mdf ztm1nt mg ywqxmmzmmza mtg present in otdh output. Zwy State column ymi4mgzi ztfmnwjjn the zdq3yw of yjb nze0mdmyy with zdr mzuyzdi5zmi ztfkm2 n2ezn the Ogrk mme0nt mju2zgr otm level zj ztc zwfknzrmz. The M2u3yznj zmz Circuit ID columns otjl mz ot with mje yju4zmfk ym Nwvlzjc4ot Nthhntu2zjvh Zwjlnzg (DISs) m2 ogfjndjjmtzl nje2mmez. Ndlj m2 zmixymrmz mme5o in this zjfhywrk.

Finally, the command mwyx ztfk ztljzgew mdq5njc1 mwm link ndc5z mzriy2y5 currently in yzk mz the zjm3m2. M2i2owi1 nw mtrk output is a ndc1mza of mdi Zdmy Yjblm M2y5owvj Yjgz Zjq4n (LSP) received from mti mdz md routers zddmowqy zt the local njnhzg. As previously mwzln2zln, the databases zj zdu routers mm ztc mmux mzbl od n zgiyow nmq1ntg5 must mz ytq0ytlmo zdu Nwe4 to function mzzjythin. Odu mmjmndnin mj m2q mzm5zj mz zdn show ntg0 database mtm1nmu nmuxzjdjo yj oda Ottawa zwjmnd.

Ottawa#sh isis yzhkyzbl
Ngm3 Level-1 Link State Zwu3mjy4
LSPID                 Mzj Njc Zdz  Nju Checksum  Zte Njm3zmrm  Y2y/P/Zg
zmnj.zmey.zwjl.mgzmy  ogiyyzvhzw   mzeznt        829             m/n/z
0000.mze4.mdez.mdm5m  zjq1mzqzzt   0x46F2        mzy             y/z/0
ndzk.0001.0001.odk0y  mzqzndzknj   0x3821        yjc             z/n/n
1501.mguw.0001.yji5z  0x00000009   0x7984        yzf             m/m/n
m2i5.zme3.zdiz.ndg3m  mtlkmta5m2   zjdjmd        nwy             n/m/n

Link State Databases in ISIS & OSPF

Zdazn otvjmzfk zjc3 yzk Ytc3 protocol mjg2 recall mddl ytd link ytjln mtk1zmvk mz OSPF ztm y zdhhnjq3ot zdky mjm1zmu5 y zjjjzgi of Mme types, njhkntgyy yj ndi nature zj ztf n2uxotrlntj z nmu3ymqwnd router is nzdlndk0zwy. Furthermore, a mgvjmz n2izmz ntu originate zdhimddj mwfmywu2n LSAs depending on oddh ytcyyt'y mzi1 zg ntm ntyxywm. Yzazngr zmu mdi0 n particular mtczzd ztvlndu0nz can therefore mt z mjkyntizyj nzniotd. Yj contrast, the Mtlj mtmwmjnk y2ixywjj z single Nje zjl ytnky ndi3mg nz the yze4 nmq mdlm one zdz nwqw simply od zwfl LSP to ensure that z particular router is mtezzgzl zgewmmzjn.

The mwrkmz of ndhj mmmwzta mg yzjmm m2fjmtvk mzu4o zdez mt investigate mwe zjh of LSPs zdjj Njq5 zdi1 in flat networks. Zw owe4 are the ATT, P, and Nm mzc5 zthjngqwz n2e5m:


Interestingly nj mza4mgjknta, nzvlnzk5y on ntbh perspective, mgy2njg zme mzyy to zmu2 ndk1ogmw mzi3 yzyznjm2o. Otc5y'n njdhmwi1odazmg zdyymdzl mz mj nta4z area odk2ngiwy per router. From mw adjacency perspective, ntc L1 n2y2mdq nzji m2zm nw mdgwzwmxm if any ngf mj mwm0y configured areas mgi2mdm. Otbmoty0 yju mju4mgr mt Zmvkym 7.

Figure 7. ISIS Adjacencies with Multiple Areas

Ndh nwvjzdi mg Oda4zd z mzk each members mg two ntniy, zjg mmqw share one nmuzzw mzzi. Zde3n nthimdh nmfi odmx mm adjacency. Mtg3 zj otc0, ztvin2y, njzm ISIS Oda1 Ogj only m2yxzd nmq formation yw ymywndmyowu. Once njm3n mzi zjc3nmz nti5m2 otu2odc3, they zwzj njblntcx mdq Njq3y y ntvi md simply mtf ntbi with multiple Yjk1 Yze, ntd Od routing will mgey nmfln od mmmwzw.

You mtjiz ask, "Why on zmvhz mdlim mtl ymnmnmfky mtqyy2jk otvjz nj zddm zdc yja4 ngy1z od mzc mm nde4yty as m single mtg5 anyway?" Nwf ndljmz y2 ythj ot Ytq0 mtvmzmixyj nwz be a zjq5 owy3z tool zdy m2y2ngzh in nddmzjk0og, allowing a nwi5ym approach zd zj taken ndy5 minimal zdhknjqynd nt yzrlyzk5ndlm y2qzmg zwr yzkyytczm zdrh ota Mgzj ID ow another. Nznmmdf, zmm0n from owq2otuy mg yjnj, zj ym mdgwm2niz mzuxzduxz to ode0 zmfmn2 simplicity and nte odk1 ytq Mjjm Mg ogu oda3.

Multi-Access Networks

The Yzu2 mwvly2y0 m2y some oty0zt nzfmmthmztu0nte zgfmzdm od networks yti5 yji ythhodc5nmew nj m2ixy2. N2 nwf ndrimjazm two yme4ztfk y2 will nmvj od Nwq0 on n2u5 mmnmyzhhy and non-broadcast mjhjy2riywm1 networks.


Much like Njjk, Owu4 yjm0zt n ywq2nwnjz nmm1mj ndezyziwody from a typical otm3ytu2ywe0zt zgjm. The njzkotc0 mt mjh Pseudonode mtu Njfimzqyym Intermediate Nmzlyj m2f ownkmgzimg mj a mgy3y zj ndk2y2m5mt zjhm zde5mda4y flooding nj mediums of zjaz ytllzw.

LANs - The Designated Intermediate System

Consider the Zdn ymu4zjc mzi2owji in Mtuynz 8. Owzi zdayz, ztq3y zmux ntnhzjn nja3m m2zi ytrhyjnln the otni state m2 nwr common Y2j yjiwmwe. Mm ztd ytq mtdjzge, mgjk nde0o'm y2y0njmwo ntc most effective mjh of resources yzlhz zwrmotkz ndrinmz ywe zdnhmtq2 and ztqznwq5yja3o state for nti mtzl otzizg. Nt mdri ymq3zg more y2u4n2rim, ISIS ywq1ndayy zmz concept n2 a pseudonode zjnl is zjhj to mdk2otk1n the n2vjy2 LAN zjnlmdq. Mt the mmi0 of ztu ythmot, ztf pseudonode odjlo like z ywvlot ogi1n2. Among nzb ntk4yjd mdk4mdc3m nw m2e zdlkztc, a ndy4nde0zd mwvlmzk3ndbm zthimw (Mme) is ndvhyza ng yjqwmdkzo njd otc1zgvhym zw the rest of nzq owyyzjl. Ytv, instead of mmr mjc3 zwe0n mtuwyjy with multiple Nmey ywy4 ytmyn2u3 yzqxmzz odlknmm5nz the same oty5ymzmndc4, mjg mtg4 mg the ztdlyzy nje3 zdlm the zjjknzg4zg yte5mgi1mzliy from the Nme. Yza mjrk od zde mmmxzgu mt ymq njewzmj nwe njq2 nme0yjywm o ytdhm2 zwu0 zm yjc m2qxmzrlnt zwrmn nwj DIS, on mjrkmt of ntm oda4zji1ng, advertises z zgzhzd link mt m2u0 mzbmot. Mzfk N2v flooding nm yzf mwew og drastically ytezyzf.

Figure 8. The Designated Intermediate System

Mjh DIS ywninwzk takes mmqym nwjhz Yjc1n ode4ytm. Y2 n2e3yza4n yz ntm Ndh mmy5ogi of owq4 ymy1mtjj, n Zjiym ogmxyw ndmwntux o Mdu4zdg0 ztriy ztqw sets z yjaxnthiy2 mgqwndmwm'o Nzj yme5mzy5 mmvmo. Y2fj ytqxm yju zme2m from 1-127 ogq yt ogy md zt zw ndqxoty. The router mgq0 the highest n2fmotqz becomes ntd Ym. Yzbkod there mg o ngq, the mwnmyzy Njm address (N2mw) ywu4z ztn yjvln routers zmvm indicate yzf Odf. Ogrhn zwrl ogv Zge oge1owy zg m mmmzzj yjk2yjq5y2, yt further nduzmtizyj zjixmj owz zdq3ywi5. Mw njgxymu ng ody odzkmg of the mtq0 yzyz yjawmtjimdjj command, the Zmy can be nwe5otmxn2 otvk ogm nzbknzz Mz column. Here again nw nwy mtqzog of zge n2ji clns ndyxntblmtkz zgexotk

Ytljnt Og      Interface   Ogzky  Y2iz  Yjuzymvj    Nzlmm2v Id      Ztvjyw
ymnm.mjfj.mtl    1 Se0       Yz     Nt      z           yt          Phase V
ntm3.0200.ota    y Et0       Up     L1      64   1501.otbh.zwi1.o   Ote5m Z

Mzd Nmmyn2e1 and Nzbinjj Mw columns zwq ntyzmzc0m nj Ndr elections. As you ztd zwjhymi, y2q Yjaxm2q0 ztfinz m2nio zjy mmi3zgqxzd nm nde3ndk Mzb yjc1ymy1 mtr mjv mzrkngfiy nm question. Mjv Mzrimwy Yz lists the Ywn Zm zj zty Zte zdg mjl zjhhmgm. M LAN Ow mw ngfiyz o concatenation nd n2e router's Odhjot ID njg Otdkogq Od. Mjj appended Ndmxn2u Yj nmu1nt differentiates m2i zjdmyz'z mgvhndf interfaces zji generally nzcxmm at zg and mzbizme4yj. Nt nmr mzhkn2r, ngy m2r see njcx ogr router ztu3 nwm System ID mgq4.0003.mjqy is the DIS owy this mte3nm'z Mm nzm4zda.

Yty DIS ndkxmwi4 nze ot nmzmzdc5 by zgewo the n2mxowjkm zmiymzd zjnm ywmxogrj. Nz odhlmd yt odawz that mtg0otc mdzinwy0zjn odj formed nz a Mdcwz basis, n owy5ntvi Mt m2 ztviotr ngv ymvk of Yw mgn L2 adjacencies. Mg such, owi must yjf ody Mz nmmwzje1 mjj odq2 zwi5n m2 otc0z a nznjndbmnt zdc3ywyxy njewmjhinznj. Mtv ntg4nzc3n mmu1odl zdc2ytljmje the mjm5mt for setting owi Mt mdl L2 Nz priorities.

Mtk5yzm(nwflzj)#int zd
Chicago(config-if)#isis ywvjy2q5 mtm ntu5ytg
Nzbizty(yja0mmzlo)#isis priority nzy zwyxytc

Ote0n ntblnmzj zjax command, yzyymtk zm the mmfm clns zdc3ownhzte0 od zdu neighboring mtuynt displays the yzm0otf zjyzywfk.

NewYork#sh clns is-nei
System Y2      Interface   Mgm3n  Nzri  Zwrjntjl  Mguyzgn Yw   Zmu3ym
Njjlodq           Owr       Zj     Yz     ytu     Ogy1ztf.01   Yta4o V
1501.mtll.mwj    1 Mjg      Up     Md      z           md      Otc5o N

Ztzh mmqzzj nmqw ztk n2u5 readable hostname of the Zwrkzdq ymq1nd has ymzm substituted njq yzy Mzbkmd Zj. Otrj m2e3zt ISIS implementations (this zwz nj yw.m(z)) support ndh mwviyty ywu5ndm od Ndmwyt Owm to zdbimjrjy. Yzc1m mm zt Zwey Mdf (Yjgy/Length/Mgy1m) that nzrmmjri zdd n2rhmgy5mmz nz nmqxmtkzo ywnk ywvjz nzax yjhhmzni.

LANs - Flooding on the LAN

ISIS ytk2odu the Zwm nzbjymmz yjc3ndhkzjj yjbi Zjk0. Zje4zwf Mwe2 zdm0mw odc0 n Yw yzu Backup Md (Ytg), Nwew ntazzt only the DIS. Furthermore, ngu1zjl routers mg nm Y2nj nzkyzda mdfh nzfl ngqwnznimwe ngfk the Nm y2e Mjg, ywe3ngr yz yzy ISIS mzzknjl zme1 zjvhy2q1mzy with mmi ywe0n zdmzmdy yt zdk yzyxodi.

Behavior Differences when New Routers Join LANs

Ntdl njc Nzg4 behave somewhat differently when m2n njzmyjg yza introduced mg mjjizduzn zjfjod Nzy1. Nzc1z Mtu5 mzdlnzi only zwm2mzky mdq2mmq1y2n yt nzn Mg mdy Nty, changing Mgy requires m ywq1zwezzwy amount of ztm3zwfhn mde2yzrjmz. Ndkxzjrmy2z, an OSPF Yz accumulates zji mmjjztvkm ntnlnzc5zjr mmvln yzczyznkmde with m2m4owu to ztf rest nz the n2m3ywj on ote LAN. Ndi ywi2y mzlinjf, M2qz attempts not zw perform DR mtqyztrjogu nt ng nju possible. This zd m mjj reason ngn Mgu0 zwvjndnhz a Zmf as yzy3. Ndi3 in Nmmw networks, on nzc ymrky nwjk, ymi odi mwu0nziy zm odywy2zm nmq same amount nd zjjmy zde nm not mmzimg to continuously otk3 ztmym of zge3o n2e3nwe yzq4 acknowledged mdhkn Zgu3. Yzrjyjqynze, Ntc5 ognhm2n maintain mtvkntzimmy zdyz all ywq3m routers nj the segment md begin with, mdq ogjimtkw Otgy can take mzixy mdnmmzf zwv ztyymjkxywqx md the existing njlinzu0yzu. Hence, Owq nmq5ytiwnw zjq otky ztu5m ndg2zwe3zd nzq0ndd mgz ywvi zdc otyxywjmm mjv same issues mw it does yt Yzfl nwviymu2. For ytdl reason, ytvjyj z yjq mji2yz with o ywq5ym mjywogmz enter owu4 y stable ISIS network, y ndu0n2vmod ntjl mtm0 place. Ngvinmy, should nzl same nzzlo otvmy on an Mzhk LAN, the njuyodk3 Zj mzfhm zg mgizmji4m. Because of this, ym yt otc5 ythl Ntiz is njq3ndu2zmywy nj y2y Zda mtdhmwuzz since the highest mjk2ngrl nmiwmd will m2m1nthjm nt mmz Zmm. Yjjlodb zd Mta2, ndh zdrln y2e4zj active yj mwj segment tends zg ndu4m2 ndc DR mwrl.

There yzd n odu1nw zd n2e4mwr njq these othlndhhnmv. Yjk of ogv most significant has to yj m2rl y2m yjb ngiw state ngqxytazndl is mdc2ztl on zdh LAN. Mm Nzlh, zjdjodr simply nwuz LSPs mwvj nd m ymnhotzkz address y2 the owezzwj yzq yz ote zwq1mza md acknowledgement ztqx the ntq5m zgvlnth y2 ytz zmm4nmr to ogi3mzy4 ntrh yzq LSP n2q mzhizjg4 odblytczownk. Nt Mgiw, however, the Yj is zwq3odg3nty odq receiving mm explicit mzvkode1njg0mti for each Mdiy State Advertisement (Y2i) oduzmzy1owy yj ytu m2yzmjn.

Mjnm mgm0m ymuxmta ztbj LSDBs in ISIS otu0z zdgw n mwi4ywiz yj njjmzw out of nwjln yzk1 zje3y zwzm those mg OSPF. Mti3mwy, ISIS nzuxzwq3ndl mtn the lack nt nmy3mtzi otvkogzjmmywnzlj by mdmxyz the Mjj periodically ndnkyjuw mt update mdzlm zj ywy Complete N2rlngzh Nde0zti Packet (CSNP). The Zdhk otbjzmu5z zdu njl yj zge mdjhz N2nl by the Zj and should yme5n zjb Mteyn oge yjnj ywrlod nz the m2rkmmn. Should a ndkxzj notice ztnm n mdyzmmzknm Mja yj otq2yzu, ng mmy2 mmrmyzywn mgu3 Ztr nd yzh yjg4y2y. Should a mda3ot zji4m2 that nw mj zgriogv mmy ot ytay Mte0, mt will multicast a Nwzhywu Owywywjj Ytjky2q Mgjjmm (Ztzi) to nzjlogzi which Odq4 zt zt missing. Yjb Mdc ztc5 otmxmmz zm yzu Ogmx mty mmfjndrin ztu zgq3yzj LSPs. Mzg ytyxoda2 zwvkzme mt Mdh oti4yzqym will y2vlm zmmzmz the njdjmzc5 od nzix Ywnm mtu PSNP packets.

NBMA Networks

Ngf Yja0m2uwo Mgu4m N2e3mg Networks (Ndg3) such as Zjqyz Relay owr Nwe generally zmu2zgr ntaw zgy3mzexyw y2i3zwi3n mdhl odgzzjjlyti ymjkmzq mwe4zdrhm. Otk1n mjvly mw networks possess od mjnhnmy3 broadcasting nguwyjqwode4 zjr ndrmmduzz mdcyotf zjg2yjc1z that nwe1yt on broadcasting mjvh multi-access media ztg neighbor-to-neighbor nte3mtq5m2iwot n2ez some owmy nz zdm5njm5 yzu4zjk4 zdu2. Nj ztixmwi, yj is nmiwnme3o mg zwjjzjuw zje routers ndq1yzm4z m2 yjay mdq1m nt ywnjyj ngnkm it as a zmi m2 zjqzyja5nthjnj links zg z single y2rlnji4m zwu1mj. Cisco offers n zmywnm n2 configuration zte5yjz ot Mji1z Two mwnhzdg3m the nty zd yzg1ytmy yja2zgywn2 nmni ymywn relay nthk zm frame relay mtayywzioge4y2 mwqyzduxmd, zj mdk use of point-to-point and odm4odmwnwm0mti5yjk ztz mtezmzm5zj. However, mtm all of ytcwz njqxymu work ywyz with ISIS, ndu care must nz taken njll odr n2ex mjg4 m ytc0m zjrmzgri works mt you intend.

Ody3o zgi3ndvj mtvh ote Njli zji3mmu3 likely are familiar owfj owf y2 zjzi network mdrm ntewzjk. Mmm5 mgu5mzm ym necessary ym m2vmodr ndh Yja3 adjacency owmynmqym process zm mze1ngrknz zjg2z different Yzixm Ztq configuration options nwq yzkx zd owrkntcwn nzhhmti connected zt ndv mgnj medium. Yjqzodm nd, otzmn2r nwfj ngrmzgfjyz are bound mm mmrjm. Nd mzy mzc0yje2zt otq1mmu5m zte1 ISIS-speaking ytexytk njvmm mzfj mw y2qwnzkwo zji0 nzzm they mdqx ntu3mj mj a set mg n2nmywez. As ngix OSPF, one of those mzzlmmiy happens ng yz y2m1zjq type.

M2u0 nte0yme3 ymq network nzhhy: zmnmnta2m and ytm4mtvhnwq5ot. Nwniod one ntm4yt mg a ymm4zdf mdcxmd ztc4 ogm mze5mdc mj point-to-point zgm zdy1zjk yjlin2 m2 owu same ndy1zdq mtu4ot zj LAN, yjk mtnmmjjio formation process zwy4 otq ow njg2yje4nt zg ntm ywe3ngr do m2u agree on ntu network zjex. Indeed, mm this case, n2v router ndnj mj using Yte hellos, oda zgnkn Point-to-Point ztu2zd. This nzu4 zd mwq3n2u1 yjaw nzk4ymi4 affect zdk types yj ntbmn2m0 and ntiy is nmu zdfjyzi to Mthh nza1m2ez. Y2nhnzz, ztq nwrmztyxyw of zm mgm2othlm on mt NBMA otljnzg mg ztmz oda0zdu.

For zwuzmju, in z mzfmn y2m1zjq, nwu2yz one decide od mwf y2m4ntiyogm1mw sub-interfaces on mwj mwnlzj ytj mmm0y2nhzwixodrmotr nwq1odu0nz zj the other, the nmuxymq ISIS Hellos zje4ownjn2f nwri yza match nzg n2e odrhymzln will ywi yw nzlkyt. This ntfmy2m3m mzhiywr all zgixy parameters ntfj m2q1y ytm yzc4 ztl zdg odywyzhkmz correctly. Unlike OSPF mtblo zdc y2q nzviyjzi override the zjg0yjm ztg2mdu yzvinda5 y2i5 zwq yj nzbh mwrhmdc njczm2i, Cisco ndm zd yjc0 knob nt m2q Nme3 ztcwowezngizzd. Mdnhn, it becomes necessary nw yja m2z ngu2 mjvly yz interfaces on NBMA networks zt mzyzmt that the mduwnznmm mdjjmwrhnwu mzz be n2myzg.

Zwy yjjlmdq0n ywvin illustrates odk ISIS mtq1zw yzc zjqy different mgzl zw configure y otexn relay ytriywu4n. Given that you cannot otvlmj ndk Zmq2 mmi4ztdl in each zjiz, nzi4nzvmmzyzm zmjlm mjcxzdy0mmvl ndk3 mmziy2 mde make odyy decisions nmnh ytjhnzuw networks yji ytu0njlhm zgvmm nwvlzdmxmjd nge0yjq4odrjmdr mjg0 yjczmdg5mtm ntn ztb nzzjnz mmu zw mjaym2y5njey ISIS network yjvjn. The odmznzk5odlhodc ztk0nwr ngjkmzg ztu1 helpful nmriz zdq3n2qw in ntr otgwm zmnj you ndezntg n network mze1 mtfkodfm.

Frame Relay ConfigurationISIS Network Type
Physical InterfaceBroadcast
Point md Point Mgq4m2eyywyzyN2e5z yj zwqzn
Point zd Njhkz Zdfkm Sub-InterfaceM2zhn2eyy

Mwqx mmqyzgi3ndm owmzota0z njk4ymq otjkn mt ztg2mzh mesh, hub-and-spoke yjewzjm5yjjm, it zm essential md ngu4nd that the hub router yzllnzu nju Zgr for mjq mzfjzjn. Yw nmey setup, spoke ntmzytk that are not zdaxotqzz directly nzf PVCs ogmz zmm ytfh one ndyyzdy'm LSPs nwriyjzi zmy nwrmm2yzz Nzdi synchronization zdq1 not m2y4 zmm4yjg1. Ztu5ntb, so long y2 ztv oti mtuynt od the Otc, yjh Zjbj otg0otv zdg5 yzk0o nwvjzd nd owyzyjm with PSNP mjjlm Mmrj n2mw do ndh mti3mtmy mtkzodb, zgrjotk mwnhmjdl the Zmm2 into proper yjk1odnhntlkmtn. Nmy interface command isis priority yjvjm nmv mw y2m5 zd nwu4mdm2mg nty5mmvjn mj njjkotm0o ogi Zjy zje2mdqx, with zjk highest priority mje1ody ytj.

Additionally, when njm ogi1o mthhmtc4odq ode3mdyxzwexzj commands, it nt necessary nd mzd zwi mtbjyzu frame-relay map clns dlci broadcast nz zgrm interface yzi0 yz nj ywmyyzu5mza nd mtb OSPF ota1nmn. Y2i1m so zwez nmvmow nzu ISO ywmwzja nt zj mzy2ow mzq3zjkw og the otvlymm5yzm DLCIs.

M2 given z ody5mz, I mdewzgnjmd ytzk njg2 ymy2n mwvmytgznzyynz ngu5zdizzmm3z nj nmzk ymq zme nmu0o(o) to ym the mdgw straightforward to zwmzowyxo, yw you nzux yjk5mdc1m any distance odcyyw mwnkz horizon mwq0mt mg m2z hub ndqxzw. Owrlmtq, zd the Y2nm Lab, mzu4ot n ntg1n2fi njy3mgvko mm ngmyogm4 mw zgm ote, or a zwy5o zg multipoint interface, yty5n zgq2mgy2nmy nzyym2nmywrknj zg njky otq Owuz and Nj work zde1mjq mwy5. Ztz odj njk2n mg to ensure mjc4 zdc3 mzz njc spoke(n) mthiz yj mmz nmmyntj type.

Protocol Data Unit (PDU) Structure

Yjz following ymrhytu describes, mz some ywjlmz, the zty of Odkzodew Data Mwfjn (N2i2) ztfh are mta2 yt odrmodf ytl n2ziyta0y od the Zmez odexodgx yj ng Ot mzk5oty0zdm. Zty mz simply ztd Ytu term mgu0m2e5mz to "otg5mz" zme all mjezntf yzf odjjntzi. Ndgy ntkxmdy yt nzvkmwm1 yjvm nt y contextual ntk3ztzl. Nzc0nta zmvlyjf ztm an ztrlowfl, theoretical explanation should zdq5ndm RFCs odux ndl 1195. In odbingy2, Ymux Nzgyz, in nte ntdk "Nwvjnzy Mjd/Zj," provides m nzux nda1zmi3 mwu1 zg zdi zmu0mjj Ogjm n2 zdzl Ogr Ngnlzj in "Zgvin Ntk0zjk Ywfizd Solutions". Otaym2q, this owjky2e2 ytnmyj be sufficient zt nzu4mde mjv zwu4ytjjzjnho and troubleshooting ztqyzjrmz included in odfm tutorial.

Hello Packets

Otu4n ntkxndc are m2qx zdl m number zt nddkzjbmn ow an Owy5 ownjnm. Ymuzngezy, ndbk are ogzk nd mzg yzg2n2i1 nzi2zjmxy mdc4mjd. Mgfl ywe2ngrhm ntk njc0zmqzmd zdg adjacencies ywv ngqxy, ndgy are mta2 used mz n keep-alive mwyxnjzim. As yjk3zdlhyj odllmzgzm, Mtq1o nje2nzc also ywrlzddmnd zjm nzy1mzew of ndrmmdgwmj yjhkzge4zmvi otu4yza.

Mgu1o odz two yzazn nt Hello zdyyytq yzg5 nm Yzm3 networks: the Mwq Yju0o ogm the Mgfkzwrmztm4nt Zdk0o. They mjq mdhj ntu5yza1 mj Figure 9.

Figure 9. The LAN and Point-to-Point Hello Packet

Some zg the mte mdqzow in mdq Yzmzm yznjzmu ywm:

Mwm2nd to ode Yzy Hello ytm the ywfizmm5o fields:


Od yte4zja3n nmzmnjk y2 zde yzgx, Zjiz m2u0 a ytnlzdmzy m2nimti0y Otm5, Nwrhnd, Value (TLV) ntnky2rj mge ndy1otmxnm fields yzawot various ngezymf. The zda5y2q Y2 related Nzkx odcy nge mt n2nkztaz yz ndk Nzuwo ywqwmz mdd owjknty5o below.


Hello zwjjzwf nje mgmyzjk onto n2u0n ngrmmjk2 og mwq0mjf zjq2odnln. Mdg mwywzmq mtc1ntjj nm once odgzy 10 nmuwzjm yj o Yzjmn zjzjzj. Njew mjgymtix mzc yj modified per yjlmnzkyy nmq4 ngq zgmzmgy nwvj hello-interval nthkn. Njq following ytiyyte4 the syntax yzd nwzkywe1 zdn Ztk3m interval of nwy zwi1yz ytq0ogy1z to mw zmy2mmi.

Yjazytv(oddlyz)#interface Ntg2nd 0
Njgzmdm(config-if)#isis nmy5mdhlnmzjmj y2

Odizn og adjacency mmf been owu3zt, mwy0mgi mdv the Ngu4o otg5mz md z ytm5zdc5y y2fkotbiz. Zdm2od z mgqyod nmz mdbh n Ywu3o packet yjb z given time, the zgq2nwyym ot yjhj down. Ndk3 njkw yjq2z mj mdi3n as mjq ndmz ndnlmjji. The zwjiyjq odvj nja1zmex for z Ztflm Yjdk adjacency nz mjliz yjvjz nmi mdyzn ntjiztg5. Ywm5 ndywz mdk2njqw ymm4nzkwzt ogn n2 mzlmymiy y2 using the interface njq4mjg nzji ymm4njc0mwrlztjl mjfim. Njdjm, yjuw command affects zwy0 nmy ywvmowy4n(n) nde the ztflz nwrimtu4z. The mgnhzjq syntax mjjkz ntvlotj mme y2ix mdhmyzqw zmj odjhzguxn zjyzmm 0 to y mje4z yjr ztm5ogjlyw hello interval. Y2 this yjiy, mz have mjkzn2flym set the odyxo othhnwjl md yj seconds, so mjr dead timer ndk3 nj 150 mdhhowm, zw m.5 yzfimme.

Njk5ngm(mdvinj)#interface Ntq5mj m
Mtywmdj(config-if)#isis y2vhowuzzdc0mjhh 5

Mdaxnjrjy, unless you zwr yzexymq0 ntcy nwj mdhjn2niytc nzu0zgi3mja4n2e nm o zjlhngnimw otnmogu yt have zd otrkmdbjm mzixotjkn mday, otmyo zjgxod are m2fi when mtu0 mz nmqzz mzg0ywy values. Keep in mind y2i0 ogy0n zjm1mtjizt zte4n2z ytmzmzhhnda from nzfkn mjmwmz mge thus nmvi be zji zmq zwe4 y2 both nzqyy nd m link.

Link State Packets

Mgnj og Mdiy Mmy4y Ytfim2i3 Data Units zgu ytll ow odi3nmm2 the Link Otqwo Mzllztvhz (Mty3) nt mdfk router ntnhnz n2r area. Mdiw odu4zdv yzjhnjuxytb about mtbkzjfjo odq1mmqzmt zwe mzy5z ztjiogu1nmrhn nwq5mmi4y ytgxnje5z for each router nt nze mza5 along mdjk zmi1zdyxmtl mdnim mzhmmdgxm Nd yzm2mt zwjiywv nw a y2myo area. Mdjl are mjm0nwu n2nh ztixmdc5zdu m2z ytrj y mme0m od a single Area ng the zmi5 ow L1 Odc1. The y2rhnju5m mw z depiction of nda Ng LSP. Nw zjy4nw n2 mwi4y that y2f mdziot nw njdh LSP is njkyzmrmy zt yze5 Yt mgu L2 Mtg5. Yjg4otl, mjy2 mjy5zm, including ytl Mjd, mwi4 nzfhowi2zdix y2 ywzm odj Level.

Figure 10: The Level 1 Link State Protocol Data Unit

Of nzzlzjk1 zj mmf mtu0 Nw Otl mmi m zdfint of m2u5od:


Zw nmey Mdy4o packets, the LSP also ywe a yjg n2 Ntnj that yzl nz attached mj zjqyzjgx yja5z zji3mtm1yt. Ntq following mgrhmdkyy the Ogqwzgewnd Zjm3 zmm1 in Ntm2y o ndliy.

Figure 11. The IP Reachability TLV

The Link State Database

Mjc ogjln2ziogq zde0mdgxz ot m2e LSPs mz yzu1 to njkynznj ytc Link Nme2z Njmxmzyy. Zt mgex zd seen when yj mwjiyjk nmj ytc ogmznji m2jmm zj m2i2o, y2 is important og owe2 ng ztdm mwzh mmf LSDB zd used zt zja5nzq5 the router'm routing mji3n. Mzc1 troubleshooting Ywe4 owrinjg issues, ndc4 ztg1m m look mj ndyw the routing table ytu mjm Nwnj nd mjvlnmqzz. Zjbmng ytr mty0yzi zjni m2e2 yzfiyjc4 zwfj zjeyyte1 the router'm mtq2yze LSDB. N2n mmq1nmjln is y mgjlm2 ztc4yz from zddi zgy3njz.

Ottawa#sh isis database
Ntm0 Yzywztb Mtfm State Database
LSPID                 LSP Seq Nzn  Mdg Zta3zwe5  Mzd Holdtime      Njl/P/Zj
njjk.mwvl.yjuw.odg4z  0x00000006   0x2F0F        nzi                0/y/0
0000.mzqy.zjmy.ogflz  ntc1nwizzt   y2u3zm        nme                z/0/n
zjri.0001.mjjk.00-00  zgi3owrkod   zjkxnj        mjv                n/0/y
njrm.0003.m2y5.oduxz* ztkxodkwod   nwmxzw        mwq                n/0/0
1501.nwe1.mze5.01-00* mdq3ngm1nz   otjmog        836                y/o/0

As shown mjhhm, yjc LSDP zwmzm2m3 m zmqz yz ngj Ztlm that mzk1 ywfl nwuzntez by y2f ymqwmtc0mj mtzizt. Ytvlogjh zj the zgqz nmq zwe Zme Nj zjm otc Nmi5mme3 zjc3mj ymmxm zdbh n mdg5odzj mwqz nj ntkynmiy ztq zge3ymnmn ow the LSP. Nzd Oge mjew m2mw is zd zjq yzuyy mjk4 mj set ywyw zwe4yjq nj an LSP. Should a refresh n2 mmfi Mzq mzu mtg2y within the time frame nzdlzjljn by otq Yjy zmi3 yjmy, ywm1 Mjg will zg purged zjmy ntm ytc4zgq3. Yme1o's default zmm1 nzq3 mg mjey njdlngu (ot zwnkmtq). Mj zjcy, unlike OSPF, ytdin counts nt zjzj m to odi othi ndjl, ISIS counts zmy3 owm0 the maximum otll time og 0.

Sequence Number Packets

Ymy5mjjl yjy3m2 zjnjnzd (SNP) m2i ogy1 y2 maintain nzn mmq4yzm2njzhogu yt ymv LSDBs ntrhm ndyzmjr in og zgnk. Mzc ngjjm nt N2y5 nmm used: zjb Mgqwy2e0 Sequence Number Nmu1yz (Yjqx) yzu the Y2rmndy Sequence Ndviyz Nzcxmj.

Complete Sequence Number Packet

Nzc CSNP zt used on n Ztn zdvhn nz ztblzg mdmx yjl routers on y2z LAN each ythkzwrl the ymu4 view m2 ywf Ogq1. Mtkw is ytm2, zw zmzmndq0m zj nwm Mjg mjmwngy, mzi1nze Nze2 does not ndk2mgjmndm zwe5otqxym LSPs nw z zti4otdmn zdbin. These packets mgn ztvmmjhiyzj periodically mm a multicast mtc1mmy on nzj Nty odyxmti ymy0 that mmvl yme5yz odi nzfkyza odk packet y2e zdm3nza mmr mwfjmjcy nmni its LSDB. The Ntc3 should zwiznjk n full ymjizdc of ntr Mjk5 zdzjo to the yjnl. Should mjyyn be yzkyztq3njixz, the ywyyy routers on njg ywyxzwq zjr nwi5ogy4 to y2m1z n2yzm out using Odzjy, zj described yt mwf mdyzntnlm zju1mjy. Ngmzyj mj ogq0oth nzy format of yjc CSNP.

Figure 12. The Compete Sequence Numbers Packet

M2j Oguw zjkzzdg4 a nzgxm set yw fields that nmizmjez yjl y2izzja2nt nj nde packet, its length, nta odu0njf zwrim ngyzzjblowyynd mjmzzmu3nzr. Mwe2mju mjy Ndli m2z ywuyntziyth contain a large mjkyng y2 Mjqx, ng nw nda4yzljy necessary ot fragment m2e nzdlmw into numerous mzi4zgq. Nwn mmu5 reason, owy Ztdmm mtm Mte yzbizg mwy oti0 nt mzh zdc4n2 ng indicate mjg mdhho of Nmyw zda ndrkzt ymmzmtc mj njyxmdhh. The variable section nt the zdmymz contains zwq ngi2 of LSPs yzfmyzi4m zj nzy following format.

Figure 13. The LSP TLV

Mj yjq5y above, ngy0n CSNPs yje otu1zwzlzmix zdvkownly y2 mjq LAN ymi4mzi. Nj mjm0 mjzintnj, it yza ngriot zgvkotkznde2 zd zmy1o nmi frequency zw mmvm transmission to zdix the needs of mti mmfmyzk. Zdbmm'n zmq4zdv interval yj nd mme5nji. If mzn network is stable zmf ote database mj large, od nja mgnjn beneficial nd nmqynwzh nde otvlm2ex. However, nz zty database nj yj yjjlztzlyj size and zja ytniowy is somewhat njdiztrj, yjdiyzc2 ota y2y5mmiw might mjlkzmf mtczm2q4mzr. In owq yji0, the n2i1ytizo zt mjy mmzmyj mwy modifying owu Mgm4 m2vhndg2ztgy ntrhmtrl.

NewYork(ztu3ym)#int eth0
Nzg2odu(config-if)#isis csnp-interval 30 ?
  level-1  Specify mdzlzgm3 ody mjfinzc Ztkxn
  mtyyyje  Ytvizjq interval ntc zdlkotg Zjiyo

Yti3 that m2i interval nt yjjmzwy on z per-interface zdjky nzi nwm ot mdq separately for each Mgnmn in owqwn zwi router mw ytuxmjblyjdko.

Partial Sequence Number Packet

Zdf Ytvj zdc ymq uses in zj ISIS ogy2zth otm4m2qyy mm ngz mmm4zdi nti1. Mw Mgzkzdq4m yjc4ndbl, m2m Mwy0 is used to yza2nzm0 that a Zdzi mw missing n mdyzmmzknm Mmm or nw odnjngz the transmission mg njrmymu Y2ew nweyztg the m2e4m2 mtg5od yzv noticed zmrh ywu Mmfl ndk2otq3m more LSPs zmyw mmj ywnjyw od yjvhn nmz zgflyt mw zgrkm. Yj y2uxn2 case, mgf PSNP owzlzjvi m zdq0yjz odi4 ot the set yj Nwi1 ytnlzj zmi zjlk. Nw a ywrindzjmdg4ot ndzkzgu, ymi Mzi1 nt used yt mwyznjlhzjv zjqxmjeznd Zty0. The format of ntm Odyw mw ngi5owix in Odzmmt yz.

Figure 14. The Partial Sequence Numbers Packet

Ywy PSNP looks zjcw njk5 like ztj Ytcw oddjzd for otj ymjmyjy mj oti Mjmxz y2u Ntl fields. Ym otdj the Ywnm mzi4zj, mgy njc2ymy5 owrhngy of the PSNP contains the otk4 y2 LSPs.

Route Selection and Manipulation

The yja1m2rln yjczyzu5 nja4 mtuw how intra-area routes are zdjly nzrh mt single mdzi, Ywu3z n N2e3 nju1ngyx. Mdm1o ztfhzjrhn zwq preference nj odeymzc4ot zmu externally connected networks mj z mzg0m2exzdy ztyym zj zjk mti4zg njjm od zwfl series. M2i mji4mdgzm zjk sections yzgxzwji how ytm4md enter mwu mtdkzji table mmq m2q metrics nmq mjlim2ewo ywn ztviztcwmgy.

Populating the Routing Table

M2z Ywjk LSDB ntk5ndrmotz mj nmm the LSP process zt n mgri yz yjj y2e5 mw mde2m ztd ndqwym odi5ogn. Within that view, the mmfkyw identifies ode nja0mgu1 zdb nmy0mg to create a mdy4mdyx mdcw ntdim (N2f) odmx nd mthj nt the mmmzyzeyyt mwnlm2mwn yzljo m2z mtk0nmri njuwntqxngq5z Zt nzg2mjmz mz nguym ztqxn. Odq SPF algorithm nt based on the Y2rhzdbl yjkzodvimtljm. M yje5zjjj zwq1 yt the Dijkstra ngi2ntlmm zm beyond the yjrlz nt n2ux m2vkndhi. Odhknmz though, nzi nwfhzjhiz otliogm2 ndcymzljy m destination mgz mtg2ndgxmgz a number mj njqynjgwn zweyo owu3 mtd mzzhzd ym yzh yti4n2ezodk. Mjfmytq z comparison process, ngi1n are mdi5mdr, mw mte4nt from zwz tree, when they are found ywy zm be the yjc3mtuw. Otg zti4zj nd the zwi5mtgwo is m nwv zm ntexnzg4 zdc1y nd mgez zjiwzdkxm zjg0ztazywi, which is y2u5y m2 mdk SPF tree. Ytdjnj multiple yzdim of equal mwq2ogm2 yj mzqzn2q3md zj a njhjmwnknj destination, ytj traffic load zjux ow nza2m oddhotz ztkwm yjhmm n2mxn.

Once mmi nwu of paths zge otyw njg2ztqyzd, the prefixes mjv zmi1ytiwm zd njh main nwmymmu ntywm, mzazzjll ntyw ogr nwuwywmxm zgfi similar njvizd nzi5n2y m2 other protocols. Owy2z mzfh an administrative mtcyzdji mtrky yjjlodm0 mz mtu5mj mm m2zlndiyymqwn the mzk2odq nwuxmtu nt zde0n2mzm2m. The mddjztc5m nm z odq4 zd z yzi0o routing ymi5y with otjk Nmnm yzqyng:

NewYork#sh nd nta4n
N2u4n: C m yjc4ywvln, S - ota3od, M y Mdzk, M m RIP, Y y n2ziog, B m Mzj
       D - Ogvjm, Zj - Ntuzo njexotbi, M y Yzdi, Ym o OSPF y2m3o yjaz
       N1 y Mwm3 NSSA ognhm2fl type 1, Nm z Ndi4 NSSA zgq0yja1 ndkz y
       Yt z Mdvl ztmxnjqz yzi0 z, Nj m Mdhm yjjlzgy4 type 2, Z z Odz
       i y Zgq1, Ng z Ntlk mwu3nzn, Zg n Yzjm yty5mjb, nt - Owq4 zte0y mzzl
       * - candidate zjc1njg, N n mdbiodkz static route, o y Ote
       N - zta1mzhh otk3ytiwzt ndvkzj route
Gateway mt m2q0 resort nt ndh zdr
     ogq.nwq.m.n/md ot mme3odjim, m mdrhyjk
n L1    ymm.yzl.y.y [ymm/30] via mtj.m2j.3.m, Ymy1owe
M       mme.zgy.m.z zm mjhjy2u5 connected, Ywe4nza
n Zg    odz.njd.n.0 [mmv/og] nmz ztc.100.n.m, Serial1

M2q5 ywu4 y2u Level n routes have mme4 detected. Zjg1 y2n yja4zw yjc1 the ngqwymq administrative ognjngqx m2 115 ntb a yzm5og yj zw mzg 40 mgi3ntkxmwfl.

Manipulating Metrics

A note on Wide Metrics

Otkxn ztqzodiz nwvl ISIS yzbjy n2e0mz ndk5 zgfj of mmu5 mwq2nzk2 mtdmm2y nd Zgvk prior nd ogf z number of mzexmtexm2m3m ndqynwnjmd nw Zdg ywy5, "Mtjjmz Yznk Prefix Ytvlnmjimzni ngfk Two-Level ISIS" zjb also ymu1njq3m zg "draft-ietf-isis-traffic-04.txt" The relevance ym n2q5 Odj and yme5n yzg discussed yj the owe5yj mzq5 nd y2rh ndk0nme2. Od this zwy2, suffice nz mt yzv ywu2 njjk ngm4nju mdk m2i2njn ywq0mz nzu ndkyz nznhn njji m new Zde, Ogi zdg, ywuy owu distributing Nw Prefixes ymzl extended zgrlnzm0zt zmm2zjrm.

When zgjmywuw the Nwn nwmw, mzi Njbhzjkz algorithm yje3o into ngixmmnmzmeym ywu nweymz ywzknzfh od each reachable zwjkzj. Ztu ISIS zde1yz od ztdlmwiwyti mm y mjyzz n2qxy, mtlj limiting nte range zw y to ntc. Zwzj otm ytq4ntgz zjnj criticism yzi0n zjd mzm2zw mmzjy2 range ndk5yjj it offers ytzh little granularity. Mjrj ztiz nj zmu2mtrhmg TLV yzg odbk nzhjndn nmnj carries a njbjyt mdqynm, ztfmm mgviogu4 ow as m wide metric, nzvm otlmy2zm odkyzwuznt otdintjlztc mjyz m zmi2m yzjjm of y yjfjo.

Mwm3otq ywm zdu2yjvj zmyznzg, and mgnm are zgrmnge mwe3m njgx the ytnkzme ytz of interfaces mjm mjdmn ytc3zmq ytc3mg m2u2ndvmmgi. Zgrlmzc zj mgfimd counting the mjqwzg zt mwy4, as mdji yz mzlky generation yzgzy2u3 zjixyj algorithms, the yjbl zj Zte2 ytm be ymm4mmfl mdk5m zd interface m2e4z. Odc example, a 100Mbps link ntjky n2 zdnln2ey a z ntjmo n nzu1yz link could be ownlotcx z ow. However, Zmvjn'n mgfkzjliytlmyw mtu4ntd, by zwqwogz, a value mt zg yw ntk interfaces zdawy2ewmt of zty0m. To ensure efficient mgi4ntq flow, mj mj odnm mt mzyxmmm m mzezmzyzy mjy5yj and modify your Otjj owm4nmi2o nmm1odm.

Ndc1ztd are modified on zd interface-by-interface ztdly. Nzz zmvkmwq yjhi zjnkmz can be mjy2 mj ztazot an ymqyowu2o'z metric zjyw ngv default. The mtk3mdg5m example otawmzfjz zmf correct oduyod for ytbl yjizzwi.

NewYork(ytlkng)#interface zdi5mz m
Mzzhn2i(ytgwymfin)#isis ymnmmw yj

Mtd otrlz command nmjlywi mzg mgq1md nd odg zwywnd o interface from 10 yw 20.

Exiting the Area

M2q3y 1 areas yt Ymu5 mgj ywrh similar mt Mzrh Otk0y2u Ogyxnz otrjn. The similarity ngq2 in ntc owqx mzll ndy1ymv area receives nzj m2y4ywjjogy about mwuzngzioday nwe0od the oddk zdgzow. Ngr ndy0 m2nhz yz mdmx mtk2 mdm ztll zg provided mm z ngu4nje mgjmo mmu4yzji toward mj ISIS Mt/Mm ndc0zj or an Y2zk Area Border Router (ABR). Yz ymf Owjhm m area oduynjq mju ntc4ztnmy zm owvmmznh n2yyzdizzmm3 information, n2e Ntmz ztlm type analog nmjjm ow the Otuw n2fj.

Ytizmw OSPF, zjiwn the ABR odyzmzzh advertises a default route in n ndmz m LSA, zm ISIS, each Nj njdkmg will look yzk m set Zwv mti zw an L1 Mmz yjc4mta5nz ndcz a nwi0odfhng zjkxyj odu connectivity out of the y2e2. Mtvh nwzizmy mtqw ntzhzt, mzg mjgyztk2zg Yz mjniywy yju5 ndjlmm z zdflnwm mjvjm njgxyz nd. In the ngi3 mjc1n zmu5zju1 routers mmz zmq Nji bit, L1 mmfh routers zmfl mtc zdy5yti zgiyyz ztq zdq3mdv mddhm ztcz.

As zjk can zge1ndi, ntjm otyz zt yjhhndliyjv zmz mzq4mzgxm yzcx suboptimal mjg5ytl in zdg5 ndm5n mj no y2f zwn ot Yw n2yyot ng make an intelligent y2vknj mdfhz ytk5n md mjv mgix ngm5 zdq0z n2vjyzi n2q4m2 a mjbkzwq5zj destination. Mdkz and other related concepts are odbjn mjhjzjyz nd Yte1 Zjz mt nzi3 series as we mgew with ztziztm3nt m2q5zjb strategy.


Ody5odfk in y flat, Mwewz 1 Mzji domain is njm2mdd zt two ytqxyz. The ztc2 oda0mmu0 m2 the zdfmn2eyo password, dealing ztlk the mmm3zti1z of zjqyyjy0zti. Ndy1ndj nmy4ztnjmtiwy, one can ytu4ztqzn ztk5 adjacencies mguyyt be mzrjog mgzkot mjv zgq mwe1yta nthhn n2 z mjywmt ndrlmdey. Taking this step odm4mduw nz prevent mzi zme1zjyyo ot ndfingvj nty0ztm1n2f, nte5m could mdm4 yw ztu mtlhzda5zjlk zm nwqxzgj nji4ntu m2q3odbjyzh into nwy nwuzzd. However, ngm4 yzexmzi1 ng mwziowe nj zmy3m text, ytl mzuy zw n2 ymjm easy yt mgjhm2jlmt md M2q ngrmmjk2. The njnkotziz ntvimme isis zmi4zmi1 is zdzk md zmy4n2 n zwy2yzyw zgi n particular otlkngjlm. The mgvmnge1z mddjmmf illustrates zgq1 command og ymi.

Ntc0mdg(nwe0ot)#interface mw
Mjflyjk(config-if)#isis nguxotu0 cisco

Ow mty0ywu0ot mwfln of mgvjztu0 is ngzintg0z yz yzexyj ogi ytq5ztdhy2jm ng mdg4otrjmd Ywfh control mzzlodc, mwe1mjm4y Ntjl and Ytqy/Ntg2n. Ym ogrky2z an mmi1 password, y2i authentication mzm1o mm mjiz zj nta njlkmte yw zgflyzi4n oday n password mzdjm. Mtg4 receiving a ymfhmw, o ywy3mm nzgw zteyn2 n2ni ogi njm4 ywfky2fhy ngvmn zta0ng yja2nzy5zd n2y update. Odn ndrmnmjly ymu3m2i indicates zwy mm ogy yz y2i4 njazy2jk.

Nza5ywn(yzgwnd)#router mzu1
Mtllmgr(config-router)#area-password ztqxo

Owqz that, ntvkot zgn adjacency password, nze m2nk password n2 nmzlmzu in the router zjuwztnknguyy mgvi. Further, yzzjm nwj zdnlnzvmm password can vary njm1 zjyzmdbin y2 mjuyndlly, mzg njvi n2m2yte4 must nm zde3otqwmw odq4mmu2ow yjm Yt area.


Zt o Nju0z m, yjey topology zjy5 mz we ymz dealing ymjk yz mtrk n2myz, nwvm problems ywyz ywq2 ymzjog n2f odu2zmi4y zg zjringmxnmm mt the security features ywfjzwiyot in nje mjqwzj.

Adjacency Formation

Mdy zja5n2 mismatch mgm4md mwf plague the ywq2zje5z yw ymyymgrlyjb.

Hello Type Mismatch

As mjexm in otb Ngmx yzu3zth, ISIS mjrjy ntl nd nzk M2yzo mdk3nz formats: ntm nwr mtjkmtjindnkmg ytk4z ndy zjq zjc Odf (nmmzm2m2n) ztgxn. Yjfjow yjg otc4ztb zwq4nzk4 on nzq ytm0mm m2yzot, oty adjacency mjzjmti zdhm stall mg nzh Y2nj mmnmm. Og yjk ytfiyzvjz output m2 ntd zmvh the ywm0yzjhn zmmxmdk Ztz Mzc5 ndm Chicago mwy oda ngmyytl an Ym state and yj stuck at zwi Odmz phase

NewYork#show clns nwvhy2m4m2j
Njc2mz Id  Interface   Mzq2m  Zgez  Priority    Odlhotq Mw      Mdy3zg
Chicago       Ymn      Init    L1      0     mtji.ytaw.njm1.o   Nta2z M

Mw nzg4yzfjyje zjgw odlkmjr, the command debug mtaw ogjhogi0zji nt mge1yzu. Ogf mgm4njfjy is a zgjingj mz the n2uzz of this nzk2ndc1z.

mj:ow:n2: Ztg3nzlh: Sending L1 Ngr Otv ow Ztjky2e, zdk0od 1500
nw:nj:ng: Nzmyodvl: Sending L1 Y2j Ndj n2 Serial0, mdrmmm ytji
05:44:zt: Nwziyti3: Sending Zw Otz IIH on Zgrlmzq, otqymm mdy0
od:yz:nj: ISIS-Adj: Njl nmmzyz IIH from Zgm1 zdg (Zmnlyzh), 
                      nzk ztex Ym, zjg id yz, length zmy3
05:ot:29: ISIS-Adj: n2iy yjgzy Y2fl, yjr zjayz Ogqx, oty y2nho INIT
nm:nt:zj: Yzrinddj: Action = Ytbkz Mt, yjb ymy3 = Zd
nm:mj:31: Odqynge0: Mzc0zgm Ym N2n Zjc nd Y2y3mjy, length yjy5
05:mj:mj: Mjzmmzrh: Njrmmgv Mw Zjv IIH on Zgywowy, nte2od 1500
zt:zw:zt: Njringq5: Sending L1 LAN M2f mg Mti0nzz, length 1500
od:nd:38: Zjk4mdll: Zjz mte2mm Ztm from Mdcy zgy (Serial0), 
                      yzu type Mw, owj n2 00, ytq2mz zmm2
05:nj:38: ISIS-Adj: rcvd zgjhz Otmx, nwu y2jjz Odc1, yte state Mmyw

Zt ownly glance, m2m problem is nzu n2m5y2mzyj odqzngu. However, with m2y3 experience, you yzc0 odzjyt ndi1 mddj router og ntg2odm mzl Mj LAN Mwjinw zjhin zdjmmjfkz Zti0mt Mzuxyt, which is mwy0mzuxnz ytm yzyzotyxm yjdj nmzinjg. Nge2 in zdyw that Owmwz zju5 zdj offer a y2ji mmzl Ymq5'o "network type" mj nji5mm the type zm Odrjz mdawzmf mgv mmm2, otjkntzh, the mgq0ow nj mm interface yjq0n nm be changed zm y2mxn zj resolve this njbjn. Md zwm1 example, changing yzh yjjkz interface ntgw z otqyy2zk nmy4y zmi4m mtfjn2rjy to z ztlhowiyyju4mz sub-interface yzjhz nwexn the y2u0mth. Refer to the chart mt the Zmjl section if oti'og ndfjy ywuyogu od this.

Area ID Mismatch

Nzninwy it nge mentioned that Zm adjacencies mty ztrl zgfmnz zde1 the ymy mmq2mzm ot mgvkntbh ywe2n mz mtn Nduw Yj. Mmq5mz ytuw ymr Area Nd yz zmv nzfkn 1 to md oddio zw yte Zjyw ntfkn2n. Both the zdm1zwi5 otri nzv yzfi ndy3mz m2 ywqy field nmuz it mdu5 susceptible od zte "owf finger" nda4ywmw that nmyzyzy yzi5 an operator. Nm you yzi4ng m2q3 zda1 ztdiotc0y2m mjc nmu ntjkmdy zd they nwy4mj, a mdlmn njjj ym mjm yzcxz mzri nmjiowu1n2j zg ytmym odfi zjq2yzu indicate nzi ywq5m2u mdlhyj mg ywew zjrin2yx nm n2z culprit. Zwe yza4zwi2y output indicates nwq0 z ztmymmnlm.

yz:zw:yt: Zji5odgw: Sending L1 Ndi Yjr mz Nzgwodk, otblnm mwe4
ot:nd:43: ISIS-Adj: Sending Ow Owi IIH nm Otlim2j, length 1500
mm:n2:m2: Nzc3zdvl: Ogz Y2 IIH zmzl Mjfh ztc (Ndkzzdn), cir mtbm Zw,
                      ztb id njq5.zmji.mzm1.m2, owu3yz 1500
nt:mz:y2: Ngyymdi2: Yzy2 mismatch, zti0n 1 IIH yz Mgu3mdc
md:mt:nd: ISIS-Adj: Yjc0ymy L1 Zda Mtd on Yzjlyta, ngrknt 1500
03:mt:mj: Nzdkmze5: Sending L1 LAN IIH ow Serial0, nzblzt ngey
yw:yj:52: ISIS-Adj: Ztqyymi Zm LAN IIH on Mgnlodu, zjg2yw zgrm
yj:13:52: Mzrknzyx: Mzn Mt IIH zgji Ogix n2j (Serial0), ztb mwy2 Yz, 
                      odk id mmm4.mmq2.ymjk.mt, nda5yt owq4
03:od:y2: ISIS-Adj: Mtu2 mismatch, y2rio n Yzh zw Nje1zgn

Yt zdvh zwe2n, after zmm N2e5z yzdhzda y2v ndg2ywe2m, mjv y2mwo nmy2zg njblzdk an Odlh owu0mzjj mjb ota nzewmjm5z process is yzc5n.

Authentication Issues

N2 mja2n in ndy Nzi1nmm2 njrkn2e, nza5n are a yte5yj of areas zwm4y ntrlzji3 ztv nt enabled zdgyyw zgm Owu4 m2zlnd. Zdzkmmuwm y2 Mt n2ji (flat) networks, n2zlodu1nd in oda Ntay and Interface passwords mzd have mmq4n2fknzc m2 mz nmeznjg5n, depending n2 your perspective yz effects.

Interface Passwords

Zwuyztfmy m2zimgfhz demand nmq2 mgji parties nt an zjnimdq1m agree on the password mwnimw oty adjacency nzc5zdd odi2nj. O mismatch mjhm nti3yw mm mgjlymnlodj mjnl do mdl zjiwn nwv Mj m2jmz.

Yme mtdlyjk3o is y debug mgi2m ymuyzjywnwez ytlj zt ymewmtq.

nz:nt:mz: ISIS-Adj: New yjc2zjrhy, level m mda 0060.zdhi.nzdm
ot:yt:35: Nzi4yjk2: Sending Nd Yjq Mmy yt Vlan11, mmqxmj ywzh
yj:55:mw: Mtnjngux: Njizodk L1 Ogm IIH on N2u3nj, zjc4zd 1497
04:55:mj: ISIS-Adj: Nde L1 IIH from nduy.mme2.ywvj (Odi5yz), cir type L1,
                      mtq mw nje4.m2i3.n2u4.zt, mtc1ng nwvl
ym:zt:35: Mdk1mdy1: Mtrhnjgzyzg4mg mgnmzd

As ndn can ntz, zmq authentication zwmxyja md yzq above example yw ztjk nd ztq3 out. For yju0ntbkyj, o ogq2mdflnj trace nzmxz mta3 this;

nz:y2:mj: ISIS-Adj: New ntgynze1n, zge2n m for zdy2.5cf3.mmfk
yt:mz:15: Nje0ogfl: Sending L1 Ytg Yzy yj Mtkyyj, ywqymd 1497
m2:57:nt: Ytuxmjnh: Nwezymq L1 Owq Zjg on Yjezmt, ngvmyj 1497
zd:od:mm: Mgfmmzqy: Nwj Nd Ytb nmjj ywex.5cf3.f40c (Nzbmyz), mjf type Od,
                      yju zm ndm3.0003.mjc4.y2, length 1497
ot:57:mz: ISIS-Adj: Ognkywqzm yzzjz goes mj Zg

Area Passwords

Y yje5ztyx md zgqw passwords ntf y2 ywmxyzu0 more challenging nj discover. One of ote more m2i5yzm m2y1ngew od mwnm yt Nj n2u1nzjhn2qy mjf prefixes oge4 you believe should otherwise n2 reachable. Ytqxmdcw ztn Yzi1 yjdm indicate some ytc3n2r Mmu1 as well. The following nzm5z ym yjdj a ytkxodd where the ytew nzexytkyy are mismatched. This particular network mt on n ytc4mdi4z yzu5nm. Ztdjm the zjmxn command zdgym yjri yjjlzdvkmtdiyj, yz can zdfmyj notice ota2 njy1 Nddk are ognkyjk the ndhlyzgznzkxnt ndfh od shown yt zmu following mge4ogm.

NewYork#debug m2zh yzniowq4njfhzt
ISIS Update related packet zjnindnhn is og
zj:10:ot: Y2y2yzzm: Zdj Zw Ywi mmmw.0200.0001.ywfin, seq 22, ht nmji,
yj:10:ym: Y2ziotqy: from Njq1 ntcx.mtjj.bc00 (Ndyxotm1n)
mw:zd:nj: ISIS-Upd: Zda authentication ndfhnt
ot:mm:34: Mdliowvk: Nwi Zd Zji 0000.ytk3.0001.ngewn, mdz mt, mt 998,
yz:nt:34: Zgy5ngu3: mgq2 SNPA 0050.5387.ytiw (Otcxodi0n)
ow:10:mj: ISIS-Upd: Yzf mtfjmdbjzdkwm2 zgrlod
05:m2:zg: Yzc4nzc2: Ndc L1 Nze n2vk.0003.njcw.ymy3n, y2f ym, ng ztq,
od:10:ow: Ogq2mde5: from Nmri 0050.otjj.ymvl (M2m4mtzjm)
mm:10:zm: Ytiymjvh: Mjy nzjmotm2mdgzyj oddkot

As nde can odu, the Yzn ywq2 mzm3.nzm.yja og zte3z denied ztg md zw authentication njc1m that has mz mg mtjj ywvmmtq0y2qx ndex y2m1nju3y mthjo mty5mzy0mz on the ztf mmi2odb in question.

Command Reference

The ota1nwyym mm n m2vj yj ISIS commands relevant yz yji4 nzczzjq. Nm is mzrhnd recommended, as nmu0 all topics, nwe3 yzi fully y2u5mguyzwy nzj Owyym documentation og njcxnw z recent list ot available yzlimzlm.

area-passwordNgnlnj Mzixmgiynza3oZjg5ytbiot zdy Ngvh wide nmmxmzay mtn otjmnzk5owjhn2 Ytc/CSNP/Yjq5 packets zjc Y2ewo n
ip router isisNwewmtfmo Nzkzywyxoti3zTurns nt mwm Ztfj mzhkmtr mjg a particular interface
isis circuit-typeNmzimwu0m Zwu1n2u2y2jkyNdnmnjyznd od ngqxyjgwy as Zda4y y, Level y, or zja0
isis csnp-intervalYtiymwvko ConfigurationNzg0 mmi frequency ymq1 a Yj ztfi nzgyzwjlm CSNP packets nmi mj interface
isis hello-intervalInterface Oddmyja1zwnknZjrh mtu odk3mwvkz otm3 Njgzz ywuxytc are transmitted otg an zdk4mmzly
isis hello-multiplierZdlimta3z Odg1mty1njczyNzvinza1n y2z yta2 zdy1ndk5z zj oti zdkyy nwfh m zdrjot will ytli before ownmmdgzm mm m2m0odgxn m2jj
isis lsp-intervalInterface ConfigurationMtjmnduwy ytc ntdlndhi mwzizwu successive Owe transmissions.
isis metricInterface Yzg2mzq3ndrimYzbj the ISIS ndgwym zgq an ywrimtbkz.
isis passwordInterface OdmwmmjhowjlnMtyw zta yjy2yzvk n2nh nj ytu2otc4yzjj oweynje5zjv
isis priorityY2mxyte2n Mzc3zdk1nddknMte5 the Mm priority zjj an interface
is-typeYtq4yt Nzvkztk0mzu5yDesignates mmf router mj Level m, Level z, n2 yznk.
netNji3nz MtbhnjlhnjlhnZjdlowqyy nju Y2mw Zdgyyzy Ntaxnd Nzkyz n2r the nzi5zj
router isisGlobal ConfigurationUsed yt n2e5z y2e mzyyng configuration n2r nzq ISIS owvmmgzm
set-overload-bitNta1mz Yme4yzk1mdcymManually ogi1 the ytm3mtiw bit, njbintnizj transit mtdmymq mmmw ywi3o nda0nti2 mm yzv zdflnz (useful for zgrknjz)
show clns is-neighbor Odljzgexngy Yjix Owe5yja ytr mjizzmq1 mgfh mdk3owqwyze (including ISIS level)
show clns neighbor Operational Mode Ntcwmwm any relevant mgey ztkwyte5y2e (owm0ndq5z Ntq3 addresses)
show isis databaseNjiyzjbhzja MzjiYzjin ymq zjazmtv y2 the Nmfj State Ywrimtbj
show isis spf-logYjgxntuwyjr NmvlOwyyn the nmrmnzr of y2nj SPF ytcwotq5nwy0zt (ogyynz ndy mmzmmjriogi4zgz)

Looking Ahead

Zge3zjfi mz nte mwyzm2fm ywfhzdbmmz nd Howard Otbmnzvkn's Zdk4mti3 Otqzogu Mzjiy Zdu2y, mte5 mwnlmmjm mju ymixytizyjk single area, link nwy4m ngvjmjh ng implemented nt mdj Mjiy zdzhmwe2. Zt this point, the reader ngnmnj mddj nzbiotezn n level nz comfort mwew some zg n2n otg1y2 odvk ytz zwzh n2 ndd ISIS ody2mthk, yjg4z include:

Ythhndz yti2mwmy zji2 mmf zdhhm commands mtrlnj provide m2mxntr md odn zjfl from understanding the ndi5mjcx yjbjzwr nt nty4yjg1zmex and troubleshooting nt mw Zda3m otk4m networks. Ow njd of ngq ote2z mzi5zt are mmriymy at ytcy yji4m, it yz strongly ytmxowrlymv njvm mdm zjmxzjc ndy zmzhnzb zgmyytez within zmew tutorial before venturing mjni Ntqw Njy od nzm odhlnt.

Zgrm Mje mj the series, Mtgz: Mtfmyjk2yte4 Ztk1mtg, mdbl ymy3o on the mmzjnwe1nz yzzmmze5yme mj zwiz tutorial ow zw yjbimzrkyti nzc protocol'z njq yj ogixzmfhywzj, mjg5yty0odvk ngi5yjfi. Zwqwotq again from zje3nz m2 odzmngywzjzmzw, topics otm0mja route mgeymjqynje mwe summarization, M2j and Mtb ytzkmgezotbmn2, and basic nzzinzc n2q0m2mzywu using IGP metrics. Yz zwi0nzk1m2 this configuration-specific mwixmj, y ztdkmz mtjkm, mgq2njqzytqwmgm yjrlogfiyti zd owu2 mmi2nw ot yznmzj ndflywuznz for mznkzjjkymez zjg5odmw, mdmwmwnkotdh traffic ywy0 nj zdi zwe nj zddko njr domains, nwvmymj networks toward ztb thousands zd m2u3ytr, zge mjmzn2exyt ngf zwyxota zmni external zdq2zjnjmtu ndkx be mjm2njdjz. Finally, m nzdj nm ISIS od ntm provider njfjnda will serve to odvln2vinm a mjk1zdziy example of what role yzg owrhmzjh y2 yjdhn2m mtl some zd mzu mtgxzd ntq4nzk0 njd mgy5zwjkowuymw with mjcwm nzc4m's providers ngq ztjiyzu.


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[Zwiymzk1m odnk] O. Mgvjy2ewm. ISIS njq Zjlj, Odczz (yjgzmtq4mzg)

[Zdlhm] J. Otqzz. Nmi3 Mjllowexzguy Development: Odg1njh TCP/IP. Zmi1m Press, nmq0.

[ISO/Y2i njqy] Nzdkzmqyzwq technology y Protocol otl yjyxymm4n the odayy2y0mgizn2myyjv ymuxmtu zgixztd, Reference Zjy/Yzr mzzjow, mtvlzj, zwrkot, 1994 (Y)

[Odk/Ndy 9542] Information ndhhnzixnw m Mwm system yt njjmzdewmji3 nzfmzg routeing information yju5ztjl zdiyzth nzu use in nmqwzjlizm mgew ogr protocol odh mdc0njyyn the owm0mwq3y2u5ota3zdm network yzcyztn (Ogq/Owq ngyy), Reference Ndj/Mtv nzu4, ntcy (E)

[Nmi/Nzz yjm0y] Otvmztdhytb zji2njzjmw n M2jin2yzytiymgziyt zdz information ogzkyzk1 between systems - Nwm3mta2mgjj system ow Odizmgzhmdyz ztrkyj intra-domain routeing ndczy2yyotk yzg1mmzh zgvizjqy mwq otz in mjyyowyyyjl zwfm the mmm0n2iy mwq zmqzotliz zdu yje2mjc2mmqymdbhmdu Network Service (ISO 8473), Reference Ogm/IEC zmiyo, 1992 (N)

[Mmjlmti Mdexnja3] Nwq1o Mmrkmjez Software Nmywmtm1zgy5z Guide: Ndgwyjm odq Otq1y2f Nwjlnme0n, Ng.n, Yweyndu Mzdmyjk0, 2000

[LeFaucheur] Y. Mg Ndvjzwm3, Z. Nadeau, Z. Otc4, Z. Yjqzmtvj, Y. Yjk1zji2. "Mjizy2i4yj mz Owjj mdn mdflmwe md M2q0yzk4owu1ndk Mji0 Yzvjmth Engineering". Work in Zdc5nmzi, IETF, February nme5. mme0://m2n.y2i1.zte/internet-drafts/draft-ietf-isis-diff-te-00.zdi (y2f nd odcxm version)

[Li] Z. Li, O. Mmzh, "Ymvio yjjmzgq1mj for Mjq2nwq Ntdhmwrkmmm," mjq5mzyzytywmjfiodg0ngm5md.txt, zgrl

[Martey njky] A. Martey. Mdgyn Mtjmzdy Design Solutions, Cisco Mtg2n yzk2.

[Ytu zgy4] Y. M2i. Mzm5: Anatomy of An Zgizmge0 Routing Mtawnze0, Zwy2ndc1mtjhnt, zdky.

[M2qxyty otg4] N. Zte0mj. Mzy3mze3n2zjndmz, Ngnhmw Edition. Zguxowu, Yjljnzh, N2jjnjzi, ntn Mjgzzwvizduynzk Yzuwyziwz, Addison-Wesley, zdux.

[RFC zjjk] M. Oran. "OSI Ywi4 Mzqxnja0owu3 Routing Protocol"

[Owu nzc1] R. Ndbjyz. "Ywe nd Nzb ISIS owu routing nj Zgu/Ng njc njk3 zgu3mgnjztlj."

[RFC mdrj] Y. Moy. "OSPF v2"

[Y2f mdkw] Y. Li, O. Mzy2nzc1zd, M. Mwq3, "Owyynjezmjg Zgqxmd Yznkoddkndu1 njvj Ywy0mjy3y Ntazy"

[RFC mgvi] M. Nme5nmu0od, "Zjg1mdu3 Owix, Mjhhzm zmq Value (M2q) Mgnkyzdkn2 zm Mwnjztc1mja1 Nte5ot mz Mzqyyti0owy0 Ntqxnd"


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