Re: [mpls] Two new drafts on (micro-)BFD over MC-LAG interfaces

Manav Bhatia <manavbhatia@gmail.com> Fri, 08 April 2016 15:04 UTC

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Date: Fri, 08 Apr 2016 20:34:45 +0530
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From: Manav Bhatia <manavbhatia@gmail.com>
To: Gregory Mirsky <gregory.mirsky@ericsson.com>
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Subject: Re: [mpls] Two new drafts on (micro-)BFD over MC-LAG interfaces
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Hi Greg,

Why cant different micro-BFD packets use the IP address of the MC-LAG end
points? Ones going to router 1 will all carry the same unicast IP address.
The ones going towards the other router will all carry some other IP
address, which would be configured along with the MC-LAG configs.

In fact i would argue that the u-bfd packets going to different routers
must use different IP addresses so that you can actually verify the data
plane liveliness. Whats the point in sending a contrived IP address if the
path that it takes is different from the other regular packets?

Cheers, Manav

On Fri, Apr 8, 2016 at 6:09 PM, Gregory Mirsky <gregory.mirsky@ericsson.com>
wrote:

> Hi Manav,
>
> thank you for sharing insight view of discussions around RFC 7130,
> extremely helpful.
>
> We believe, and Jeff is co-author of RFC 7130 too, that MC-LAG presents
> different case and the compromise that you’ve pointed too is justified. We
> will add more details on the potential differences between unicast and
> multicast fast paths in the next update.
>
> We are open to the discussion and always welcome comments and alternative
> proposals.
>
>
>
>                 Regards,
>
>                                 Greg
>
>
>
> *From:* Manav Bhatia [mailto:manavbhatia@gmail.com]
> *Sent:* Thursday, April 07, 2016 7:39 PM
> *To:* Mach Chen
> *Cc:* Gregory Mirsky; rtg-bfd@ietf.org; mpls@ietf.org;
> draft-tanmir-rtgwg-bfd-mc-lag-ip@tools.ietf.org; rtg-bfd-chairs@ietf.org;
> mpls-chairs@ietf.org; Alia Atlas (akatlas@gmail.com)
> *Subject:* Re: Two new drafts on (micro-)BFD over MC-LAG interfaces
>
>
>
> I believe it had to do with multicast datapath (especially link local)
> being different from the unicast datapath in most routers. Using link local
> multicast IP addresses may not necessarily guarantee Unicast IP
> reachability.
>
>
>
> When writing 7130 we spent quite a bit of time ensuring that we dont carve
> out a special data path for the micro-BFD packets. Using link local would
> have made it a lot simpler.
>
>
>
> And this is where i think the current proposal is flawed -- they use link
> local multicast to ensure IP unicast reachability which is incorrect.
>
>
>
> Cheers, Manav
>
>
>
> On Thu, Apr 7, 2016 at 11:16 PM, Mach Chen <mach.chen@huawei.com> wrote:
>
> Hi Greg and all,
>
>
>
> I just have quick review on the drafts. If my understanding is correct,
> the idea is to use multicast destination address other than unicast address
> when  sending BFD packets over LAG links. And actually this idea has been
> proposed in https://tools.ietf.org/html/draft-chen-bfd-interface-00 (the
> predecessor of RFC 7130). And at that time, the co-authors of RFC 7130 did
> discuss the idea of using multicast destination address, but for some
> reason I forget now(I may need to reiterate the discussions on the
> archive), the idea was abandoned, although I still think multicast
> destination address is a smart idea.
>
>
>
> Best regards,
>
> Mach
> ------------------------------
>
> *From:* Rtg-bfd [rtg-bfd-bounces@ietf.org] on behalf of Gregory Mirsky [
> gregory.mirsky@ericsson.com]
> *Sent:* Tuesday, April 05, 2016 6:16
> *To:* rtg-bfd@ietf.org; mpls@ietf.org
> *Cc:* draft-tanmir-rtgwg-bfd-mc-lag-ip@tools.ietf.org;
> rtg-bfd-chairs@ietf.org; mpls-chairs@ietf.org; Alia Atlas (
> akatlas@gmail.com)
> *Subject:* Two new drafts on (micro-)BFD over MC-LAG interfaces
>
> Dear All,
>
> two new drafts, related to RFC 7130, were published before the meeting:
>
> ·         BFD on MC-LAG interfaces in IP network
> <https://tools.ietf.org/html/draft-tanmir-rtgwg-bfd-mc-lag-ip-00>
>
> ·         BFD on MC-LAG interfaces in IP/MPLS network
> <https://tools.ietf.org/html/draft-tanmir-rtgwg-bfd-mc-lag-mpls-00>
>
>
>
> Greatly appreciate your reviews, comments, questions and suggestions.
>
>
>
> Regards,
>
>         Greg
>
>
>