Subject: [VRRP] accept_ mode and neighbor solicitaion (NS) pkts

From: "Stephen Nadas" <[email-masked]>
Date: Thu, 8 Nov 2007 11:04:04 -0600

Hi John, Don, Bob,

I'd like to clarify what packets accept mode = off should apply to as
follows: 

Suppose router A is IPv6 address owner of ipa, and router B backs up
ipa.  Suppose also that  accept mode is in its default state of off on
B.  Further imagine, if you will, a client with an (unsophisticated)
neighbor unreachability detection implementation, by which I mean the
client sends an neighbor solicitaion (NS) msg, gets a reply, sets a
timer, when timer pops, sends another NS msg (ie, client doesn't follow
the SHOULD about using higher layer info to infer forward progress).   

Finally, suppose that in between NS requests made by client, VRRP
mastership for ipa switches to router B.  

The draft says: 

   Accept_Mode             Controls whether a virtual router in Master
                           state will accept packets addressed to the
                           address owner's IPvX address as its own if it
                           is not the IPvX address owner.  Default is
                           False.

So, when NS pkt arrives at rtr B while it is master, rtr B drops it bcos
acccept mode is off.  Client will looses its address mapping for ipa (at
least for a time).  In analogous IPv4 case, ARP pkt won't make it to IP
layer, presumably ARP req/resp will flow and address mapping will not be
lost.   

I'd like to add text in next spin of draft to the above para to clarify
that accept_mode doesn't apply to NS requests, which we think resolves
this.

Comments or objections?  There's at least a question in my mind about
whether there are other IPv6 ICMP (control fn related) pkts that
accept_mode should not apply to.

Thanks,
Steve     

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From: "John Cruz (johcruz)" <[email-masked]>
Date: Thu, 8 Nov 2007 09:59:14 -0800

Hi Steve,

I think that accept-mode is for accepting packets to the virtual
address for management purposes. It can also be used by applications
and other protocols so that rest of the world knows only about
the virtual address. As an example, OSPFv3 can use the virtual
link-local address for running the protocol. Since way, adjacent
routers will consider the VRRP group to be as if there it was only
router with one IPv6 address. For this to work, OSPFv3 control
packets to the virtual link-local address should not be dropped.

So, would it be possible that we define "accept-mode" only for virtual
addresses whose scope is global? This way, all packets to link-local
virtual addresses are always accepted.

John

> -----Original Message-----
> From: Stephen Nadas [mailto:[email-masked]] 
> Sent: Thursday, November 08, 2007 9:04 AM
> To: John Cruz (johcruz); Don Provan; [email-masked]
> Cc: [email-masked]
> Subject: accept_ mode and neighbor solicitaion (NS) pkts
> 
> Hi John, Don, Bob,
>