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Re: Detecting router id change in p2p-over-lan connection

Hi Sunil, Nitin, and Mitchell,

As Dave points out, a point-to-point network is explicitly defined as a connection between
a single pair of routers. Also, RFC 2328 dictates that router-id be used to identify neighbors
on point-to-point links. Hence, what draft-ietf-isis-igp-p2p-over-lan-05.txt is recommending
is to take the path of least resistance and handle router-id changes by letting the current
adjacency time out before forming a new one. Another option for point-to-point links would
be to force the neighbor down when a router-id change is detected. If you do something
more clever like using the source address as a hint to determine if the router-id has changed
or maintaining more than one adjacency, there is no guarantee that other implementations will
do the same.

IMHO, we shouldn't try and optimize for the router-id change case nor should we try
and specify precisely how implementations should handle router-id changes at this point
in the OSPF protocol evolution. I'll discuss this with the authors of
draft-ietf-isis-igp-p2p-over-lan-05.txt.

Thanks,
Acee

Sunil Patro wrote:

Mitchell,

I guess we can compare the IP src address of the neighbor to find out if

the new router-id is coming from the same neighbor or a different
neighbor.

Btw, I am unclear about your reference to L1 and L2 needing separate
hellos.

Quoting your last line - " Normally if one changes a router-id, then they don't expect that
the former/old adjacency will be used with the new router-id."

I am guessing  you mean that anytime there is a router-id change in the
neighbor, the neighboring router should tear down the adjacency by
sending appropriate hello with the old router-id (by not including our
router id in the neighbor list) and then sending a new hello with a new
router-id.

In any case, can we say that section 4.5 is unclear about handling
router-id change? And it is left to the implementor to find the best way
to handle the router-id change?

Thanks,
Sunil



-----Original Message-----
From: Mailing List [mailto:OSPF at PEACH.EASE.LSOFT.COM] On Behalf Of
Erblichs
Sent: Friday, February 17, 2006 8:09 PM
To: OSPF at PEACH.EASE.LSOFT.COM
Subject: Re: Detecting router id change in p2p-over-lan connection

	Not reading the draft. :^)

       The 4.5 section only deals with matching hello types
       and circuit types for established adjacencies. The section
       does not include that L1 AND L2 need separate hellos.

       Their is no mention about changing router-ids. However,
       if I remember my IS-IS correctly, (yes, I have also coded
       for the IS-IS / ES-ISL3 protocol) then the MAC value
       would be the same even with a different system-id. There
       is a presumed single MAC per interface per router versus
       normally a single MAC value for an entire host system.

       The same would be true for OSPF, that the interface
       should have the same MAC value even though the router-id
       might have changed. However this does not hold true
       if a vendor has also switched interfaces or circuits
       that is forming the adj as these other interfaces would
       have a different MAC value.

       Thus, you can tell if a router has changed router-ids.
       However, this still presumes that you have kept dead
       nbrs/peers history and that you have made a check against
       matching died nbr/peers.

Normally if one changes a router-id, then they don't expect


that


       the former/old adjacency will be used with the new router-id.

       Mitchell Erblich
       -------------

Sunil Patro wrote:


The same draft talks about ospf in sec 4.2.
I guess they don't have a draft named separately for ospf.

Thanks,
Sunil



-----Original Message-----
From: Mailing List [mailto:OSPF at PEACH.EASE.LSOFT.COM] On Behalf Of
Erblichs
Sent: Friday, February 17, 2006 7:41 PM
To: OSPF at PEACH.EASE.LSOFT.COM
Subject: Re: Detecting router id change in p2p-over-lan connection

Sunil,

     The doc that you refer to is a IS-IS RFC draft and
     you sent the question to a OSPF mail alias?

     Mitchell Erblich
     --------------------

Sunil Patro wrote:


Hi everyone,

According to section 4.5 in draft


draft-ietf-isis-igp-p2p-over-lan-


05.txt,


"If the circuit is configured as point-to-point type and


receives


LAN hello packets, the router MUST discard the incoming


packets;


If


the circuit is a LAN type and receive point-to-point hello


packets,


it MUST discard the incoming packets. If the system ID or the
router ID of incoming hello packet does not match the system


ID


or


the router ID of already established adjacency over this


p2p-over-lan


circuit, it MUST discard the packet. The implementation


should


offer


  logging and debugging information of the above events.",

My question is how does one detect a router-id change in this


scenario


then?


thanks,
Sunil