RE: Can Multihop BFD be protected using RLFA backup?

<stephane.litkowski@orange.com> Fri, 18 January 2019 08:22 UTC

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From: <stephane.litkowski@orange.com>
To: Muthu Arul Mozhi Perumal <muthu.arul@gmail.com>
CC: "rtg-bfd@ietf.org" <rtg-bfd@ietf.org>
Subject: RE: Can Multihop BFD be protected using RLFA backup?
Thread-Topic: Can Multihop BFD be protected using RLFA backup?
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Date: Fri, 18 Jan 2019 08:22:09 +0000
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Hi,

When you are using multihop BFD RFC5883 you are not monitoring an LSP. When IPFRR is activated, the primary goal of your BFD probe does not change and is still not to monitor an LSP but the remote IP destination. So it makes sense that FRR just pushes it stack without changing anything in the BFD encaps.
In addition, I don’t think that it will be easy from a dataplane point of view to change the BFD encaps on the fly during FRR.

Brgds,

From: Muthu Arul Mozhi Perumal [mailto:muthu.arul@gmail.com]
Sent: Thursday, January 17, 2019 12:02
To: LITKOWSKI Stephane OBS/OINIS
Cc: rtg-bfd@ietf.org
Subject: Re: Can Multihop BFD be protected using RLFA backup?

Hi Stephane,

Thanks for your response. Please see inline..

On Thu, Jan 17, 2019 at 3:27 PM <stephane.litkowski@orange.com<mailto:stephane.litkowski@orange.com>> wrote:
Hi,

I think that the fact that “control” packets can benefit of FRR is really implementation dependent. It is also linked to the place where BFD packets are created (RP or LC).
From a theoretical point of view, nothing prevents FRR to be used as for any packet generated by the router itself.

Do we know of any implementation that provides RLFA FRR protection to multihop BFD packets?

Regarding the encapsulation, if your BFD client is using RFC5883, this will not change during FRR, the FRR will just push labels on top independently.

The primary reason for my question on encapsulations is because RFC 4379 has the foll. as one of the reasons for using the destination address in 127/8 range for IPv4 (0:0:0:0:0:FFFF:7F00/104 range for IPv6) for diagnostic packets sent over MPLS LSP:
   1. Although the LSP in question may be broken in unknown ways, the
      likelihood of a diagnostic packet being delivered to a user of an
      MPLS service MUST be held to an absolute minimum.

Since multihop BFD uses a routable destination address, wondering whether there would be any issues if multihop BFD packets are sent over the RLFA backup path without following RFC 5884 encapsulation..

Regards,
Muthu

Again, the possibility to get FRR is really implementation dependent, as the forwarding decision of the BFD packet may not be taken by the network processor of the LC.

Brgds,

From: Rtg-bfd [mailto:rtg-bfd-bounces@ietf.org<mailto:rtg-bfd-bounces@ietf.org>] On Behalf Of Muthu Arul Mozhi Perumal
Sent: Thursday, January 17, 2019 10:16
To: rtg-bfd@ietf.org<mailto:rtg-bfd@ietf.org>
Subject: Can Multihop BFD be protected using RLFA backup?

Hi All,

Multihop BFD (RFC 5883) packets are sent over UDP/IP. The encapsulation used is identical to single hop BFD (RFC 5881) except that the UDP destination port is set to 4784.

Now, suppose on the ingress node there is no IP/LFA backup path for the destination address tracked by multihop BFD, but there exists an an RLFA backup path to that destination. In this case, is multihop BFD expected to be protected using the RLFA backup path i.e should multihop BFD packets be sent over the RLFA backup path if the primary path goes down?

If multihop BFD packets are to be sent over the RLFA backup path, what encapsulation should the ingress use? The encapsulation specified in RFC 5883 or the encapsulation specified in RFC 5884 (MPLS BFD)?

Please let me know you opinion.

Regards,
Muthu

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