Click the exhibit. Assuming the network is IPv6 only, which of the following configurations on the Alcatel-Lucent 7750 SR router A can establish an IPv6 BGP session to router B?

Question

Options

• AA. router-id 10.10.10.1 group "IPv6_iBGP" family ipv6 peer-as 65540 neighbor 2001:DB8:2::2 exit exit
• BB. group "IPv6_iBGP" family ipv6 type internal peer-as 65540 neighbor 2001:DB8:2::2 exit exit
• CC. group "IPv6_iBGP" family ipv6 type internal peer-as 65540 neighbor 2001:DB8:12::21 exit exit
• DD. group "IPv6_iBGP" type internal family ipv6 neighbor 2001:DB8:2::2 exit

• A
  78% (18)
• B
  13% (3)
• C
  4% (1)
• D
  4% (1)

Explanation

Option A is correct because in an IPv6-only network, BGP cannot automatically derive a router-id (a 32-bit value) from an interface address since there are no IPv4 addresses present - the router-id 10.10.10.1 line explicitly provides that required identifier. It also correctly specifies family ipv6, the right neighbor address (2001:DB8:2::2), and peer-as 65540 to define the iBGP relationship.

Option B fails because it omits the mandatory router-id configuration; without it, BGP has no 32-bit identifier to use in an IPv6-only environment and cannot initialize a session.

Option C has the same missing router-id problem as B, and additionally uses the wrong neighbor address (2001:DB8:12::21 instead of 2001:DB8:2::2), making it doubly incorrect.

Option D omits both router-id and peer-as, leaving the BGP group incomplete even though type internal is present.

Memory tip: Think "IPv6-only = no free router-id" - BGP's router-id is always a 32-bit (IPv4-format) value, so on a pure IPv6 router you must always supply it manually or BGP won't start.

No community discussion yet for this question.