[rbridge] Developing a hybrid router/bridge.

[Radia Perlman]

I'm confused. I don't see what that text from mobileIP has to do with 
this proposal.
I think my proposal has nothing to do with ARP. I'm just proposing 
something that
would make it impossible for an IP packet that had been forwarded across 
the campus
by one RBridge to be accidentally re-sent over the campus by another 
one. I was
marking a data packet in a way that would be (hopefully) ignored by all 
IP nodes,
both v4 and v6, and IP routers as well.

The suggestion is that a packet that has been handled by an RBridge on 
this virtual subnet
have a dummy layer 2 source address. Other RBridges, would notice the 
layer 2
source address and not ever forward such a packet across the same 
virtual subnet.

I thought it would work, and I asked Erik Nordmark whether in all cases 
IP nodes
ignore the layer 2 source address on received packets and he said yes.

I could imagine uses of the layer 2 source address. An obvious potential 
use for it is
to refresh an ARP cache. DECnet certainly did that sort of thing. It's 
not inconceivable
that some IP implementation might do that even though it's not mentioned 
in any spec.
But from asking around, nobody has told of a case in which this would be 
a problem.

So hopefully, Alper, you just misunderstood my suggestion.

Radia


Alper Yegin wrote:

>>How about having a specific, constant MAC address, say "X",  that
>>    
>>
>means
>  
>
>>"transmitted by an RBridge".
>>When an RBridge decapsulates an IP packet onto the destination LAN, it
>>can set the source
>>address in the layer 2 header to be X. The rule will be that an
>>    
>>
>RBridge
>  
>
>>is not allowed to forward a packet that has layer 2 source address=X.
>>    
>>
>
>This would break RFC3344:
>
>   While the mobile node is away from home, it MUST NOT transmit any
>   broadcast ARP Request or ARP Reply messages.  Finally, while the
>   mobile node is away from home, it MUST NOT reply to ARP Requests in
>   which the target IP address is its own home address, unless the ARP
>   Request is unicast by a foreign agent with which the mobile node is
>   attempting to register or a foreign agent with which the mobile node
>   has an unexpired registration.  In the latter case, the mobile node
>   MUST use a unicast ARP Reply to respond to the foreign agent.  Note
>   that if the mobile node is using a co-located care-of address and
>   receives an ARP Request in which the target IP address is this care-
>   of address, then the mobile node SHOULD reply to this ARP Request.
>   Note also that, when transmitting a Registration Request on a foreign
>   network, a mobile node may discover the link-layer address of a
>   foreign agent by storing the address as it is received from the Agent
>   Advertisement from that foreign agent, but not by transmitting a
>   broadcast ARP Request message.
>
>But I'm not sure who deserves the blame :)
>
>Alper
>
>
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