Subject: Re: Re: [VRRP] ARP REPLY IN VRRP

From: "ashish thakur" <[email-masked]>
Date: 5 Nov 2002 04:52:23 -0000

Thanks bill , section 8.2 speaks when VRRP router restarts and on 
configuring and initializing interfaces .
I am not able to trace anywhere in the RFC , about ARP response 
 from VRRP router being an address owner in Initialize state . 
Either he should not respond or if so should respond with Virtual 
Router Mac Address .
8.3 speaks of Proxy ARP , but whether it is applicable for router 
in Initialize state . I think it would have been much clear if the 
response to ARP request is also mentioned in the Initialize 
state.

thanks
ashish thakur

On Tue, 05 Nov 2002 Bill Fenner wrote :
>
> >...If we now send an ARP request
> >to the virtual ip address, then R2 will respond back with 
>source
> >hardware address in ARP reply packet as the virtual router 
>MAC
> >address and also R1 will reply back with source hardware 
>address
> >in ARP reply as the physical MAC address of the IF1 interface 
>.
>
>Section 8.2 says:
>
>    When a VRRP router restarts or boots, it SHOULD not send any 
>ARP
>    messages with its physical MAC address for the IP address it 
>owns, it
>    should only send ARP messages that include Virtual MAC 
>addresses.
>
>This seems to preclude R1 replying with its physical MAC 
>address.
>
>   Bill
>_______________________________________________
>vrrp mailing list
>[email-masked]
>https://www1.ietf.org/mailman/listinfo/vrrp

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---

From: Mark Smith <[email-masked]>
Date: 05 Nov 2002 17:48:21 +1100

There is a ARP related issue here which isn't clearly covered by the RFC
- when the Master router comes up, there is a chance that it will ARP
for the host, before the host ARPs for it. Eg external traffic targetted
at one of the end hosts as the first packet exchange with the devices
being protected by VRRP.

In this case, it is also important that the router use the Virtual MAC
address in the ARP request it makes, as the target host will cache MAC
address of the VRRP router, in addition to replying to the VRRP router
with an ARP reply.

This section of the RFC is a bit confusing. The title is "Host ARP
Requests", so it doesn't appear to apply to ARP requests made by the
VRRP router.

On the other hand, the text Bill quoted says "ARP messages" from the
VRRP master router, rather than requests or replies, so the text does
specify the behaviour I mentioned in paragraph two.

I've read this section quite a number of times, as I've been bitten by
the fault I describe in the first paragraph. Upon reading Bill's quote,
with out having the seen the section title, I read it correctly, and now
realise the VRRP ARP request / reply behaviour is specified correctly.

It looks like the vendor of the equipment I was using fell into the same
trap I did when they implemented VRRP.

There probably would be value in changing the title of this section in a
future revision of this RFC, and possibly expanding the different ARP
request / reply behaviours.

Regards,
Mark.

---

From: Mark Smith <[email-masked]>
Date: 05 Nov 2002 18:58:56 +1100

A minor clarification ... the situation I'm talking about is from VRRP /
router cold start, not when a VRRP backup takes over from a failed VRRP
master.