Subject: Re: [PATCH v2] bonding: send IPv6 neighbor advertisement on failover

From: Brian Haley <[email-masked]>
Date: Fri, 10 Oct 2008 12:04:15 -0400

Jay Vosburgh wrote:
> 	As a semi-related question, what does IPv6 do if it receives a
> gratutitous NA, and finds a duplicate?

If a node has an IPv6 neighbor entry and receives an unsolicited NA it 
will change it's state to stale, forcing a re-lookup on the next 
transmit.  An un-solicited NA will change the state to reachable.

> 	I agree that doing DAD would update the switches, peers, etc,
> but, if I'm reading the IPv6 code correctly, the delay between probes is
> one second (nd_tbl.retrans_time), and it looks like there's an initial
> delay of up to 1 second as well (in addrconf_dad_kick, the
> rtr_solicit_delay).  For failover purposes, we want to issue the
> gratuitous ARP or NA packets immediately with a minimal delay between
> probes.

Right, and since a bond failover event should be rare, I think sending 
the NA immediately is OK.  All those random delays are meant to cover 
the case, for example, when a router sends an advertisement with a new 
prefix - you don't want everyone that receives it to do DAD immediately 
since it could overwhelm the network.

-Brian