The MPLS WG Archive

["Arashmid Akhavain" <arashmid@nortelnetworks.com>]

Title: RE: [mpls] Requesting your feedback - issues/errors/clarification s

Packet misrouting can happen under the following circumstance.
Consider the following L3-VPN network

A----------B----- ... ------Z

+ B sends a label mapping message for loop back address of Z to A using
  the independent control mode of operation. Let's call this label L10.

+ Z advertises label L100 for one of its VPN routes to A via MP-BGP.

+ B could also be a PE and could have allocated label value L100
  to one of its links to a CE device it is connecting to.

+ Receiving L10 for the loop back address of Z, A will be under the
+ impression
  that it has a full path to Z.

+ A starts transmitting packets with outer label L10 and inner label
+ L100. Meanwhile
  no label representing the loop back address of Z has arrived at B.

+ B receives the labeled packet and pops L10.

+ B then proceeds with the processing of L100.

+ B recognizes L100 as a local label and transmits the un labeled packet
+ to the
  wrong CE device.

Arashmid

-----Original Message-----
From: Bob Thomas [mailto:rhthomas@cisco.com]
Sent: Monday, August 30, 2004 12:58 PM
To: Akhavain, Arashmid [CAR:NP62:EXCH]
Cc: mpls@ietf.org
Subject: Re: [mpls] Requesting your feedback - issues/errors/clarification s

> Please see my comments below:
>
>
> + I agree with Luca. I have not seen much use for loop detection in
>   DU mode of operation. So, it would be nice to either clarify its
> use.
>
> + I also agree with removal of the HOST FECs. Although they are
> + supported
>   by the protocol, I have not seen them being advertised.
>
> + I agree that the selection of FECs for which LDP sends label mapping
> + message
>   should not be a requirements of the protocol spec. The FECs should
> be either
>   determined by the applications as Ina mentioned, or controlled via
> policies.
>
> + As for the use of DU in conjunction with independent control mode of
> + operation,
>   I agree with Vach that DU and IC can result in black holes or packet
> misrouting

How does it result in "misrouting"?

>   in the network. The scheme works fine for IP forwarding, but as Vach
> pointed out
>   in his e-mail, it creates issues in VPN networks.

It seems to me that the appropriate place to address this issue is in the protocol applicability document (i.e., rfc3037 as opposed to rfc3036).

Bob

> Arashmid
>
> -----Original Message-----
> From: Luca Martini [mailto:lmartini@cisco.com
> <mailto:lmartini@cisco.com> ]
> Sent: Thursday, August 26, 2004 5:19 PM
> To: Ina Minei
> Cc: mpls@ietf.org; vach.kompella@alcatel.com
> Subject: Re: [mpls] Requesting your feedback - issues/errors/clarifications
>
>
> Ina,
>
> Please note the following points:
>
> - the LDP loop detection mechanisms do not make much sense in DU mode.
> This is the hop count TLV,  and the Path Vector TLV. ( When LDP
> interoperability testing was just starting , I had most vendors out
> there remove it for DU mode ). We should add something explicitly that
> says that these TLVs should not be used in DU mode. ( This is the
> current practice in all implementations that I know of )
>
> - The Host FEC is accepted by most implementations I worked with , but
> sent by none. So I also think it's probably a good idea to remove it.
>
> Luca
>
>
>
> Ina Minei wrote:
>
> >>>Issue: do we really have to send all FECs in our database whenever
> >>>we have an LDP session between two peers?
> >>>     
> >>>
> >>This should not be a requirement of the protocol spec, the
> >>application which is using the protocol should determine which FECS
> >>get sent.
> >>   
> >>
> >
> >     I agree. This is not a specification issue, but rather a
> best-practice
> >based on the application for which the protocol is used. If you only
> >need the loopbacks as FECs for your application, then it is best if
> >you _ask_ LDP to only redistribute the loopbacks, because it will
> >make your network easier to troubleshoot.
> >
> >                             Ina
> >
> >
> > 
> >
> >>>Issue: with all the combinations of Downstream Unsolicited,
> >>>Downstream on Demand, Ordered Control, Independent Control, etc.,
> >>>it makes sense to define a mandatory combination.  DU/OC seems to
> >>>be the favored one.
> >>>     
> >>>
> >>I believe  this would  put a majority  of the  deployed LDP speakers
> >>out of spec.  Such a change cannot be made as part of going to DS.
> >>
> >>   
> >>
> >
> >_______________________________________________
> >mpls mailing list
> >mpls@lists.ietf.org https://www1.ietf.org/mailman/listinfo/mpls
> <https://www1.ietf.org/mailman/listinfo/mpls>
> >
> > 
> >
>

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