Implementing MP-BGP Multiprotocol to Border Gateway Protocol

[JMarquez99]

Hello! Can someone please help me answer these questions in my lab activity having the information from the attached screenshots below for every question. The pdf file of my lab activity is also attached at the bottom most. 

1. What is the difference between the "local AS number" and the "AS" number displayed in the list of BGP neighbors?

2. In the first output show bgp ipv4 unicast, why is 10.1.2.1 the preferred next hop address for 192.168.1.0 instead of 10.2.3.3?

3. Why do some entries in the show bgp ipv6 unicast output include a next hop address of "::"?

4. Why does the output for the show bgp ipv6 unicast command include the link-local address following the global unicast address?

5. Why do some entries in the show bgp ipv4 unicast neighbors output include a next hop address of 0.0.0.0 and the show bgp ipv6 unicast neighbors output includes a next hop address of "::"?

6. If R1's 2001:db8:acad:1000::/64 network went down, what would be the effect, if any, on the routing tables of R2 and R3? Explain.

I would really appreciate to have your feedbacks.
TIA

[Cristian Matei]

Hi,

   1. Local AS is the BGP AS number that your router runs into, the AS value from the "show bap ipv4/ipv6 unicast summary" is the AS number used by your BGP neighbors.

  2. In the BGP best-path selection, first criteria is highest weight (0 for both, so there is a tie), highest local preference (default 100 as it does not show up, so there is a tie), originated (none, so there is a tie), shortest AS path, and in here the second path wins with a AS length of one AS (1000) as opposed to other path which has an AS length of two AS'es (300 and 1000)

  3. "::" in IPv6 means all zeros, so this is a substitution for 0.0.0.0 as next-hop in IPV4, which means the prefix is connected to the router and locally injected in BGP, thus next-hop is self in the local BGP table.

  4. Per the RFC, if the next-hop IPv6 value and the BGP peering session share a common subnet (first 16 bits), the link-local address can and should be included in the BGP update for the IPv6 NLRI. This matches your case.

  5.  Same as answer to question 3.

  6. As that prefix is injected and advertised into BGP, it means that if it goes down, R1 will send a BGP Withdraw messages for that prefix, which will make that prefix be removed from the BGP table of R2 and R3, thus from the RIB of R2 and R3.

Regards,

Cristian Matei.