about IPv4 and IPv6 on the same router (dual stack) with IS-IS

about IPv4 and IPv6 on the same router (dual stack) with IS-IS
A . …
B . IS-IS
C . …
D . …

View Answer

Answer: B

Explanation:

– Cisco added multitopolgy support for IS-IS to increase flexibility within dual-stack environment.

– Two TLVs added:

• IPv6 reachability TLV

• IPv6 interface address TLV

– Multi topology IS-IS:

• A separate topology is kept for both IPv4 and IPv6 (some links may not be able to carry IPv6 –> Avoid traffic black-holed)

• This mode removes the restriction that all interfaces on which IS-IS is configured must support the identical set of network address families.

• A separate SFP per address family.

• Wide metric must be used.

– Single-topology IS-IS:

• One SPF instance for both IPv4 and IPv6.

• Easier to administer but network must be homogeneous.

• Due to consistency checks, a router running IS-IS for both IPv4 and IPv6 does notform an adjacency with a router running IS-IS for IPv4 or IPv6 only. Disable consistency checks to maintain adjacencies active in heterogeneous environments. ForL1 links, this is primarily done during transition.

• As in any IS-IS design, L2 routers must be contiguous. IPv6 adjacency checks are notdone on L2 links.