Subject: [VRRP] newbie vrrp question

From: Mark Duffy <[email-masked]>
Date: Wed, 22 Oct 2003 17:11:35 -0400

Hi, and apologies if this has been covered before.

The latest draft (and RFC 2338) is quite clear that the router in Master state

     - MUST NOT accept packets addressed to the IP address(es) associated
       with the virtual router if it is not the IP address owner.

What is the reason for this?

Accepting packets for connection-oriented protocols might not fare too well 
if a reelection happened in the middle, but I don't see how it would 
"break" the vrrp protocol to accept these packets.  And it seems as though 
having the virtual router respond to ping would be quite helpful for 
troubleshooting.  I have noticed that a major-vendor router accepts ping, 
telnet, etc. on the virtual router IP address when it is master, even when 
it is not the address owner.

Thanks, Mark

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From: Bob Hinden <[email-masked]>
Date: Wed, 22 Oct 2003 15:29:12 -0700

Mark,

>Hi, and apologies if this has been covered before.

Yes, it has.  Someone should write a VRRP FAQ....

>What is the reason for this?

The reason for not accepting packets addressed to the IP address of the 
owner, if not the owner, is to make it easier to detect that one of the 
routers is down.  People have had problems with other redundancy protocols 
that did not have the behavior that their network management systems would 
not detect that one of the routers had failed because the IP address still 
responded to pings, SNMP queries, etc.  It is also confusing for routing 
protocols.  The desired behavior when one of the routers fails is to have 
user traffic keep flowing, but to have all network management bells start 
ringing.

>Accepting packets for connection-oriented protocols might not fare too 
>well if a reelection happened in the middle, but I don't see how it would 

Time to call the IETF protocol police :-)

Bob