Re: Two MAC addresses for a same IP Primary address

Don,

> What you are missing is that there is no relation between the
> source IP address in an IP packet and the source MAC address
> in the ethernet packet carrying it.

I definitively agree, that's why I was suspicious with our understanding 
of the RFC !

> 
>>Moreover, the source MAC address of the the ICMP, TCP, ARP
>>packets related to the *IP Address Owner*, must (of course)
>>be the *Virtual Router MAC Address*.
> 
> 
>>Conclusion: a *Primary IP Address* can have two MAC
>>addresses !!!, the *Virtual Router MAC Address* and
>>the MAC address of the NIC !
> 
> 
> The VR IP address "has" one MAC address: the VR MAC.

Here, what you call VR IP address is defined by *IP Address Owner* into 
the RFC, isn't it ?

> ARP should always advertise that mapping and no other.
> But this has no relevance to the selection of source
> MAC address when transmitting a packet.

I agree that Address Resolution (ARP) of *IP Address Owner* must only 
adverise the *Virtual Router MAC Address*.

> In particular, you realize that there is only one reason, ever,
> to use the VR's MAC address as the source of an ethernet packet,
> and that is to teach the ethernet switching infrastructure
> where to send packets with that MAC address as the destination.

Of course, it is the basic goal of VRRP.

> That is accomplished by sending the advertisement packets with
> the VR MAC address as source since those packets are known to
> be sent at the appropriate times.

Please, here, when you write "by sending the advertisement packets with 
VR MAC address", please, what is the IPv4 source address ?
   1-> the *IP Address Owner*
   2-> xor the *Primary IP Address*

Our issue is related to the fact that 2 IP addresses are defined into 
the RFC *IP Address Owner* and *Primary IP Address*. It is clear how the 
*IP Address Owner* must be used with the VR MAC address on many gateways 
running VRRP on a same link, but it is unclear for the *Primary IP Address*.

I would be interested in better understanding how is supposed to be used 
the *Primary IP Address* on 3 gateways running VRRP on a same link:
   -> There are 3 *Primary IP addresses* at least, aren't there ?

   -> Are these 3 *Primary IP addresses* reachable at anytime even if 
the gateway is in the backup state ?

Thanks,
   Vincent

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