Static Routes With Next Hop As An Exit Interface Or An IP Address

[nezhad]

I have always wondered: Why would you want to also specify the link-local address of the next hop in an IPv6 static route if you are already specifying the outgoing interface, which is sufficient by itself?

[RyanB]

In short, I think it has to do with Neighbor discovery's ICMP redirect messages.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6/configuration/15-2mt/ip6-15-2mt-book/ip6-icmp-redir.html

A device must be able to determine the link-local address for each of its neighboring devices in order to ensure that the target address (the final destination) in a redirect message identifies the neighbor device by its link-local address. For static routing, the address of the next-hop device should be specified using the link-local address of the device; for dynamic routing, all IPv6 routing protocols must exchange the link-local addresses of neighboring devices.

Edit:

Mark Holm posted this way back which is along the same lines: https://learningnetwork.cisco.com/thread/83948

Im unsure if this is the only reason though.

[nezhad]

But as I mentioned the command without the link local and only the exit interface also works. 

[Harold Ritter]

Hi Nezhad,

This does not work on an interface that requires neighbor discovery (ND). For IPv4 we have proxy ARP, that allows the router to reply to a ARP query for a destination that is not on the local subnet. There is currently no equivalent for IPv6 (proxy ND).

Regards,

[nezhad]

what doesn't work? specifying only the outgoing interface? but it does. It's supposed to. You don't need to specify the link local address of the next hop necessarily.