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Occasional Contributor II
Posts: 18
Registered: ‎08-11-2015

Controller doesn't accept IPv6 fe80::1 as default gateway

According to rfc4861 8.3 [1], a statically configured route should (or at least, one should be able to) be specified using the link-local address of the router. However, configuring fe80::1 as the default route doesn't work. No IPv6 connectivity.

 

If I configure a glocal 2001: IPv6-address as the default gateway on the controller IPv6 connectivity is restored.

 

[1] https://tools.ietf.org/html/rfc4861#section-8

MVP
Posts: 447
Registered: ‎11-04-2011

Re: Controller doesn't accept IPv6 fe80::1 as default gateway

I have never tried to set a local-link address as the default gateway, as local-link address are 'local' so can't be routed. After reading the RFC, I was unable to read the same, what I read is that section 8 is about redirects that are being sent by the default gateway in case there is a better router for the destination host on the local subnet. Comparable to the ICMP-redirect for IPv4.

 

From what I understand, I have not ever seen setting fe80::1 as default gateway (you also should configure your router with that IP in order for it to be reachable), not that this will have some serious issues in hosts with multiple interfaces, like a loptop with wired and wireless. What I do see is that my Linux host resolves the default gateway to the local-link fe80:: address for my router:
default via fe80::7444:1ff:fe84:adc3 dev eth0  proto ra  metric 1024  expires 1585sec

 

While I put the global 2001: address as my default gateway in the config. On my Aruba controller I see the global 2001: in the routing table an neighbor table. I don't see an RFC violation in that latter behavior and it seems even more secure than accepting unprotected redirect packets.

 

Also my Ubuntu Linux box refuses to take fe80::1 as default gateway:

 

ubuntu-server:~ [65] % sudo ip -6 route add default via fe80::1
RTNETLINK answers: Invalid argument

 

This behavior makes perfect sense to me as well....

 

Can you explain what you are trying to accomplish, and, where this limits you in your deployment?

 

 Herman

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Occasional Contributor II
Posts: 18
Registered: ‎08-11-2015

Re: Controller doesn't accept IPv6 fe80::1 as default gateway

Well the mac-address of the network interface isn't routable either, and it still works :) The comment that statically (manually) added routes should be assigned to link-local addresses is a quote from Pekka Savola, one of the editors of said RFC. That was admittedly a few years ago, though.

 

When adding a route where the next hop is a link-local address, one has to define the interface as well.

 

ip route add default via fe80::1 dev eth0

 

Works in ubuntu. This was a minor annoyance for me, I will use the global-address instead.

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