controlling the LLA used by radvd for RAs

[Supermathie]

TL;DR: We are running into a situation where radvd is picking the source IP for outgoing advertisements that don't want it to use.

radvd version: 2.17, debian package 1:2.17-2

Our setup:

• each server has a globally routable /64 network configured on a local bridge (for docker containers)
• this network is advertised to other servers via radvd:

  interface int {
      AdvDefaultLifetime 0;
      AdvSendAdvert on;
      MaxRtrAdvInterval 12;
      route 2001:db8:f00:d2::/64 {
          AdvRouteLifetime 900;
      };
  };
  

• our edge servers also have this but also have a VRRP IP configured for outbound traffic
• IPv6 VRRP requires the first address in a VRRP group be an LLA for the VRRP router (we choose fe80::ffff:ff here)

   inet6 fe80::ffff:ff/64 scope link nodad
      valid_lft forever preferred_lft forever
   inet6 fe80::5054:ff:feed:f5a6/64 scope link
      valid_lft forever preferred_lft forever
  

The end result that we want to change is:

• radvd chooses the fe80::ffff:ff address for its advertisements instead of fe80::5054:ff:feed:f5a6

This is bad for us since that's a VIP and can move between machines.

Things we've tried:

• changing the VRRP configuration so that the address is /128 and marked as deprecated:

   inet6 fe80::ffff:ff/128 scope link nodad deprecated
      valid_lft forever preferred_lft 0sec
   inet6 fe80::5054:ff:feed:f5a6/64 scope link
      valid_lft forever preferred_lft forever
  

  result: no change; fe80::ffff:ff is still picked as the outbound address

Any suggestions here to accomplish what we want with radvd as-is?

Can we tell radvd to use a specific address as the advertisement source for this route?

Should it be modified to not choose deprecated or /128 addresses as the source for advertisements?

[robbat2]

#127 will help with this issue, but probably further work is needed, as you also want to avoid /128 addresses, and that code is driven by lifetime, not the /128 or the deprecated flag (which can be present even with a high lifetime)