Re: Virtual MAC really necessary?

Hello Keegan

Thank you for your answer. I do not fully agree to your first statement.
RFC 3768 mentions that the virtual MAC address has to be:  
00-00-5E-00-01-{VRID} (in hex in internet standard bit-order).
And according to http://www.firewall.cx/multicast-intro.php, this would  
not be an Ethernet Multicast Address. If so, it would be  
01-00-5E-00-01-{VRID}.

> If the gateway mac was suddenly a
> physical address you may run into issues if some of the attached devices
> don't receive the gratuitous arp or don't process it because of security.

This is exactly my question. Do you know of any devices that ignore  
gratuitous ARPs?

Best regards,
Roland



On Mon, 14 Jan 2008 17:59:55 +0100, <[email protected]> wrote:

> The advantage of the virtual mac is that it is a multicast address so  
> both
> devices should receive the traffic regardless of their failover state.
> Also, the virtual mac allows failover with out any of the devices having
> to change their arp entry.  The gratuitous arp just serves to update the
> forwarding table in the switch(s).  If the gateway mac was suddenly a
> physical address you may run into issues if some of the attached devices
> don't receive the gratuitous arp or don't process it because of security.
>
>
>
>
> "Roland Abt" <[email protected]>
> 01/14/08 11:31 AM
>
> To
> [email protected]
> cc
>
> Subject
> [VRRP] Virtual MAC really necessary?
>
>
>
>
>
>
> Hello everybody
>
> I want to implement my own VRRP protocol. The protocol itself is not that
> tricky, but using a virtual MAC seems like a big hurdle to me. The
> standard states that the MAC address of the new Master has to be  
> published
> in a gratuitous ARP (request/reply). I think this already should help to
> update the ARP table of every device. Does anybody know of a situation
> where publishing the physical MAC would cause any trouble? Are there any
> known devices that would not update their ARP table in case of such a
> gratuitous ARP?
>
> Best regards and thanks in advance for your time,
> Roland
>
>
> PS:
> According to the Ethereal Wiki (http://wiki.ethereal.com/Gratuitous_ARP)  
> a
> gratuitous ARP can be either a request or a reply. Any experience which
> one is better?
>
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>
>



-- 
---
Roland Abt
Geiselweidstrasse 21
8400 Winterthur

phone: +41 52 534 4533
mobile: +41 76 503 2828
email: [email protected]

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