ipv6 tunneling

Raptien

Can anyone explain why automatic tunnels can't support IGPs?

CCNAwannabe

IPv6 auto tunnels use the destination address as a way to know where to tunnel the info. So the tunnel wouldn't know where an IGP multicast should go because the destination is not known to the auto tunnel and can't be created. Just remember GRE = IGP.

Raptien

That makes sense, but wouldn't it be simple to create some sort of next hop mapping list so that multicasts could be sent to each tunnel endpoint? If each tunnel interface is configured with an ipv6 from which the ipv4 address can be determined, wouldn't a list of next hops under the tunnel interface resolve the problem?

CCNAwannabe

I found this which might be helpful. Cisco 6to4 Relay Service - ARIN IPv6 Wiki . Why do you need an IGP with auto tunnels? All 6to4 tunnels know of each other. On the IPv4 side you would use an IGP to distribute the routes. So that the tunnels could forward traffic.

Raptien

It's not a requirement, it's just something i was trying to figure out for the sake of understanding. In the ROUTE cert guide it is stated that the tunnels do not need to but also cannot support IGPs. I recognize why an ipv6 IGP is typically not needed, but when using global unicast addressing the static routing config made me question why an IGP wasn't used. There's still no major need, the static routing config is relatively light, but an IGP could do the job if there was just a way to know which next hops were associated with a tunnel interface. On top of that, i just like to question everything in order to really understand the concepts

Thanks for the link, i'll have a read.