[c-nsp] Microsoft multicasted cluster vs. Cisco IOS

[David Sinn]

RFC 1812 strictly precludes routers from accepting ARP's where the 
returned MAC address is a multicast one:

3.3.2 Address Resolution Protocol - ARP

[SNIP]

    A router MUST not believe any ARP reply that claims that the Link
    Layer address of another host or router is a broadcast or multicast
    address.


Vendor H's implementation isn't far off what Cisco used to do:  Punt 
all the packets to software because you aren't expecting a multicast 
MAC mapped to a unicast IP.  It's really just a strict interpretation 
of the above.

David

On Nov 4, 2005, at 6:03 AM, Tim Franklin wrote:

>>> I quickfixed this with a dirty 'arp' command on both routers:
>>>
>>>         arp 10.106.49.6 03BF.0A6A.3106 arpa
>>
>> Yeah - there is a MS technote about this (can't find it right
>> now...). Routers won't learn a multicast MAC address for a unicast IP
>> address. You've done exactly what they suggest...
>
> Thanks guys, that's useful to know - I've been puzzled by recent 
> customer
> requests to configure static ARP for these kinds of cases, wondering 
> why we
> can't just ARP for the address as normal.
>
> (As a side point, at least Cisco let you configure it if you have to -
> Vendor H force you to turn an obscure 'safety catch' off before you 
> can use
> a multicast MAC address in a static ARP entry at all...)
>
> Regards,
> Tim.
>
> -- 
> ____________   Tim Franklin                 e: tim at colt.net
> \C/\O/\L/\T/   Product Engineering Manager  w: www.colt.net
>  V  V  V  V    Managed Data Services        t: +44 20 7863 5714
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>
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