Subject: [VRRP] Regarding virtual link local usage for ipv6 VRs

From: Amit Mandal <[email-masked]>
Date: Sat, 15 Jun 2013 03:08:20 +0530

Hi,

The idea of auto-generating a virtual link local address is good (as
supported by quite a few vendors), but there's one problem about this
 approach that I needed some clarification on.

In RFC 5798, the address owner is defined as

    'The VRRP router that has the virtual router's IPvX address(es) as
real interface address(es).'

Only the owner is allowed to respond to control packets for the virtual
address (unless accept_mode is true).

Now if the auto-generated link-local is used as a virtual IP on a VR, then
by definition there can't be any owner for this address (since its not on
any real interface) and hence using priority 255 for this address doesn't
seem to agree with the RFC very well. Also, there won't be any system who
will respond to the pings to this address, which doesn't look like such a
good idea either.

This same constraint applies to manually configured virtual link-local
address (unless the user decides to have the same link-local address on the
interface).

My understanding is that a virtual IP(v6) address is supposed to be in the
same network as a real interface to allow dynamic routing to be seamless in
the event of VRRP switchover.

If this understanding is correct, then this consideration doesn't apply for
IPv6 link-local addresses and they don't necessarily be present on a real
interface.

Hence, I think the term 'owner' needs a special consideration for the
link-local addresses to allow for cases of auto-generated virtual
link-local addresses and manually configured link-local addresses not
present on real interfaces.

 For link-local address the 'owner' can be simply defined as the node
with priority 255, and these addresses may or may not be on a real
interface.

Rgds

Amit