| Exam 642-883 | Question id=3437 | IS-IS, IPv4, and IPv6 in Service Provider Environments |
In which network environment is IS-IS adjacency check important?
| A. |
in a multitopology environment where there are different instances of IS-IS running on the same router | |
| B. |
in an IPv4/IPv6 environment and running single-topology IS-IS | |
| C. |
when a level L1/L2 IS-IS router is neighboring with a Level 1 only or Level 2 only router | |
| D. |
when IS-IS neighbors are in an NBMA environment like over Frame Relay | |
| E. |
when IS-IS neighbors are in a broadcast environment like an Ethernet LAN |
Perform this task to disable protocol-support consistency checks in IPv6 single-topology mode.
For single-topology IS-IS IPv6, routers must be configured to run the same set of address families. IS-IS performs consistency checks on hello packets and will reject hello packets that do not have the same set of configured address families. For example, a router running IS-IS for both IPv4 and IPv6 will not form an adjacency with a router running IS-IS for IPv4 or IPv6 only. In order to allow adjacency to be formed in mismatched address-families network, the adjacency-check command in IPv6 address family configuration mode must be disabled.
Entering the no adjacency-check command can adversely affect your network configuration. Enter the no adjacency-check command only when you are running IPv4 IS-IS on all your routers and you want to add IPv6 IS-IS to your network but you need to maintain all your adjacencies during the transition. When the IPv6 IS-IS configuration is complete, remove the no adjacency-check command from the configuration.