Re: [Isis-wg] Re: Inconsistent view of routers over a LAN

Naiming Shen <naiming@REDBACK.COM> Tue, 10 June 2003 21:14 UTC

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Date: Tue, 10 Jun 2003 14:14:20 -0700
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From: Naiming Shen <naiming@REDBACK.COM>
Subject: Re: [Isis-wg] Re: Inconsistent view of routers over a LAN
Comments: To: Cheng-Yin.Lee@alcatel.com
Comments: cc: Tony Li <Tony.Li@procket.com>, Jeff Learman <jlearman@cisco.com>, isis-wg@ietf.org, Acee Lindem <acee@redback.com>, l2vpn@ietf.org
To: OSPF@PEACH.EASE.LSOFT.COM
In-Reply-To: Mail from "Cheng-Yin Lee" <Cheng-Yin.Lee@alcatel.com> dated Tue, 10 Jun 2003 16:43:12 EDT <3EE642E0.F617107F@alcatel.com>
Precedence: list

i don't think l2vpn wg needs to do much. when use link-state igp
in those places, ALWAYS assume it's unreliable. just use p2p. period.

 ] Jeff, Tony, Acee,
 ] Thanks for your clarification.
 ] L2VPN WG is defining emulated LAN (and broadcast network for IP traffic)
 ] service over IP/MPLS network and some of the mechanims being defined can
 ] result in loss of communication among a subset of routers on the
 ] emulated LAN (even if all the nodes in the underlying IP/MPLS transport
 ] network are reachable).
 ] Some of the discussions have been how tolerable are routing protocols to
 ] this type of problem, if it is worth fixing some L2VPN WG mechanisms to
 ] prevent this problem, how feasible are these L2VPN solutions, are these
 ] not well-known problems ...
 ]
 ] I hope the L2VPN WG would consider these issues and requirements in the
 ] L2VPN solutions.
 ] Perhaps a more detailed understanding of how things work/don't work may
 ] help L2VPN WG develop/appreciate solutios that will work well with
 ] routers for e.g, in case of (i) below, what would an emulated LAN user
 ] observe in the routed network (is this predictable/unpredictable?)
 ]
 ] Thanks
 ] Cheng-Yin
 ] p.s I have cced l2vpn, but pls feel free to respond only to the relevant
 ] WG as is appropriate.
 ]
 ] Tony Li wrote:
 ] >
 ] > We should also point out that in case i) things are truly broken and
 ] > in case ii) the DR will not form an adjacency with A and the protocols
 ] > will be able to tell that things are broken.
 ] >
 ] > Tony
 ] >
 ] > |    -----Original Message-----
 ] > |    From: Jeff Learman [mailto:jlearman@cisco.com]
 ] > |    Sent: Tuesday, June 10, 2003 9:29 AM
 ] > |    To: Cheng-Yin.Lee@alcatel.com
 ] > |    Cc: Mailing List; isis-wg@ietf.org
 ] > |    Subject: Re: [Isis-wg] Re: Inconsistent view of routers over a LAN
 ] > |
 ] > |
 ] > |
 ] > |    This violates the transitivity requirement stated in ISO 10589.
 ] > |    You can't run ISIS on a subnetwork where this happens.
 ] > |    At least, that's the theory ;)
 ] > |
 ] > |    At 11:52 AM 6/10/2003, Cheng-Yin Lee wrote:
 ] > |    >Hello,
 ] > |    >Just got some private responses, perhaps I should clarify.
 ] > |    >This is in context of an emulated LAN, and I am not
 ] > |    looking for a fix in
 ] > |    >routing protocols.
 ] > |    >
 ] > |    >Thanks
 ] > |    >Cheng-Yin
 ] > |    >
 ] > |    >Cheng-Yin Lee wrote:
 ] > |    >>
 ] > |    >> Hello,
 ] > |    >> What happens if for some reason Router A can't reach
 ] > |    Router B, but
 ] > |    >> Router C can reach A & B (and vice-versa), when Router A,B,C are
 ] > |    >> connected over a broadcast network or LAN.
 ] > |    >>
 ] > |    >> E.g. in the case for (OSPF and IS-IS) where:
 ] > |    >> i) C is the DR
 ] > |    >> ii) B is the DR
 ] > |    >>
 ] > |    >> Thanks
 ] > |    >> Cheng-Yin
 ]
 ]
 ] > Hi Cheng-Yin,
 ] >
 ] > What I've recommended in the past for these situations is to force
 ] > the routing protocol to view the underlying network as a P2MP
 ] > (Point-to-Multi-Point) network. Many vendors support this. For
 ] > example, in our implementation you'd simply configure:
 ] >
 ] >    router ospf 1
 ] >     area 0
 ] >      interface backbone
 ] >       network-type point-to-multipoint
 ] >                o
 ] >                o
 ] >           < the rest of the OSPF config>
 ] >                o
 ] >
 ] > Good Luck,
 ] > Acee
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 ] Isis-wg@ietf.org
 ] https://www1.ietf.org/mailman/listinfo/isis-wg

- Naiming