Re: Virtual MAC really necessary?

Sylwester,

I see your point. But sending multiple ARP Requests would not be an  
unsolvable problem :)
Again, has anybody seen devices ignoring gratuitous ARPs? And what kind of  
gratuitous ARP should be used (request or reply)?

Best regards,
Roland




On Mon, 14 Jan 2008 18:37:29 +0100, Sylwester Chojkiewicz  
<[email protected]> wrote:

> Using the physical MAC address may also contribute to opening of another
> issue: a race conditions when two Standby virtual routers compete for  
> Master
> state.
>
> The specific situation occurs when two Masters become active  
> approximately
> at the same time. As a result of protocol defined arbitration mechanism,  
> the
> Master with lower primary IP address will be forced to switch to Backup
> state.  It is fine as long as out of these two Masters, the legitimate  
> one,
> which will remain its status, will be also the last one who has sent the
> gratuitous ARP (just considering the IPv4 case).
>
> However, what will happen if the gratuitous ARP from the legitimate  
> Active
> is overwritten in device by that one coming from virtual router that will
> assume the Standby role?
>
> After receiving advertisement from another virtual router, should not the
> legitimate Active re-broadcast the gratuitous ARP - just in any case -  
> even
> after a short delay?
>
> Sylwester
>
>
>
>   _____
>
> From: [email protected] [mailto:[email protected]]
> Sent: Monday, January 14, 2008 12:00 PM
> To: Roland Abt
> Cc: [email protected]
> Subject: Re: [VRRP] Virtual MAC really necessary?
>
>
>
> 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>
> 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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