Question 1.
Should LSRs know about all the labels used within MPLS?
| a) |
Yes, because labels are globally significant. |
| b) |
Yes, because LSRs must exchange the labels. |
| c) |
No, because labels are locally significant. |
| d) |
No, because the labels are not used in routing the MPLS encapsulated packets. |
Answer
Question 2.
What are the functions of an LSR?
| a) |
An LSR, or Label Source Router, is a router, performing only encapsulation and decapsulation of a packet. |
| b) |
An LSR, or Label Switched Router, performs encapsulation and decapsulation into/from an MPLS header as well as label switching. |
| c) |
An LSR, or Label Source Router, performs encapsulation and decapsulation into/from an MPLS header as well as label switching. |
| d) |
An LSR, or Label Source Request, is a message type that RSVP uses when setting up an MPLS tunnel. |
Answer
Question 3.
What are the fields of the MPLS header?
| a) |
An MPLS header consists of 8-bit Label, 8-bit TTL, 3-bit Experimental, and 1-bit Stack fields. |
| b) |
An MPLS header consists of 16-bit Label, 8-bit TTL, 2-bit Experimental, and 1-bit Stack fields. |
| c) |
An MPLS header consists of 16-bit Label, 8-bit TTL, 1-bit Experimental, and 1-bit Stack fields. |
| d) |
An MPLS header consists of 20-bit Label, 8-bit TTL, 3-bit Experimental, and 1-bit Stack fields. |
Answer
Answers
Question 1.
Should LSRs know about all the labels used within MPLS?
| a) |
Yes, because labels are globally significant. |
| b) |
Yes, because LSRs must exchange the labels. |
| c) |
No, because labels are locally significant. |
| d) |
No, because the labels are not used in routing the MPLS encapsulated packets. |
Answer
| c) |
No, because labels are locally significant. |
Explanation
MPLS labels are locally significant. LSRs use labels in forwarding the MPLS encapsulated packets to the next LSR only.
[4702]
Question 2.
What are the functions of an LSR?
| a) |
An LSR, or Label Source Router, is a router, performing only encapsulation and decapsulation of a packet. |
| b) |
An LSR, or Label Switched Router, performs encapsulation and decapsulation into/from an MPLS header as well as label switching. |
| c) |
An LSR, or Label Source Router, performs encapsulation and decapsulation into/from an MPLS header as well as label switching. |
| d) |
An LSR, or Label Source Request, is a message type that RSVP uses when setting up an MPLS tunnel. |
Answer
| b) |
An LSR, or Label Switched Router, performs encapsulation and decapsulation into/from an MPLS header as well as label switching. |
Explanation
LSR means Label Switched Router. It is a router that can perform MPLS switching based on the label. Also, an LSR performs packet encapsulation into an MPLS header and packet de-capsulation from an MPLS header.
[4703]
Question 3.
What are the fields of the MPLS header?
| a) |
An MPLS header consists of 8-bit Label, 8-bit TTL, 3-bit Experimental, and 1-bit Stack fields. |
| b) |
An MPLS header consists of 16-bit Label, 8-bit TTL, 2-bit Experimental, and 1-bit Stack fields. |
| c) |
An MPLS header consists of 16-bit Label, 8-bit TTL, 1-bit Experimental, and 1-bit Stack fields. |
| d) |
An MPLS header consists of 20-bit Label, 8-bit TTL, 3-bit Experimental, and 1-bit Stack fields. |
Answer
| d) |
An MPLS header consists of 20-bit Label, 8-bit TTL, 3-bit Experimental, and 1-bit Stack fields. |
Explanation
An MPLS header consists of 32 bits, which are: 20-bit Label, 8-bit TTL, 3-bit Experimental, and 1-bit Stack fields.
[4704]
[IE-MPLS-SQ1-F03]
[2002-03-28-01]
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