[rbridge] Developing a hybrid router/bridge.

[Alper Yegin]

Mobile node (the host) and the foreign agent (mobile node's first-hop
router) rely on parsing the L2 header on the IP packets sent between the
two, in order to learn the L2 address of the other, rather than using
ARP.

If you are setting the L2 source address on the original L2 header to X,
this causes problem.

Am I missing something?

Alper








> -----Original Message-----
> From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org]
On
> Behalf Of Radia Perlman
> Sent: Friday, May 14, 2004 5:06 PM
> To: Developing a hybrid router/bridge.
> Subject: Re: [rbridge] Developing a hybrid router/bridge.
> 
> 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
> >
> >
> >_______________________________________________
> >rbridge mailing list
> >rbridge at postel.org
> >http://www.postel.org/mailman/listinfo/rbridge
> >
> >
> 
> 
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