Re: [Idr] Error in draft-ietf-idr-sdwan-edge-discovery use of Encapsulation Extended Community

[Susan Hares <[e-mail]>]

Linda:

The only version of draft-ietf-idr-sdwan-edge-discovery published is -12.

Sue

From: Linda Dunbar <[e-mail]>
Sent: Tuesday, February 27, 2024 6:04 PM
To: John Scudder <[e-mail]>
Cc: [e-mail]; [e-mail]
Subject: RE: Error in draft-ietf-idr-sdwan-edge-discovery use of Encapsulation Extended Community

John The Encapsulation Extended Community is only in the client routes BGP UPDATE, which is the BGP-based VPN/EVPN client routes UPDATE message. There are no sub-TLVs added. Section 6's first paragrap
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John

The  Encapsulation Extended Community is only in the client routes BGP UPDATE, which is the BGP-based VPN/EVPN client routes UPDATE message. There are no sub-TLVs added. Section 6's first paragraph states the Client Route UPDATE follows the BGP-based VPN/EVPN client route UPDATE message..

The sub-TLVs discussed in the draft are under the Tunnel Encapsulation Path attribute in a separate UPDATE (U2 in the document) which DOES NOT have Encapsulation Extended Community for SD-WAN edges to advertise the information about their WAN ports. Please see below for the details.

p.s. Are you referring to version-20?

Linda
-----Original Message-----
From: John Scudder <[e-mail]<mailto:[e-mail]>>
Sent: Tuesday, February 27, 2024 2:42 PM
To: [e-mail]<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>
Subject: Error in draft-ietf-idr-sdwan-edge-discovery use of Encapsulation Extended Community

Hi Authors, WG,

I just noticed draft-ietf-idr-sdwan-edge-discovery-12 and was looking at its use of RFC 9012. There seems to be a fundamental misunderstanding of how the Encapsulation Extended Community can be used, and I thought you should be aware of it. TL;DR, you’re specifying the use of SD-WAN-Hybrid tunnel type in an Encapsulation Extended Community, but this isn’t allowed. Details follow.

[Linda] That is just an example for needing a different Tunnel Type in the Encapsulation Extended Community

- RFC 9012, Section 4.1 tells us that the only permissible use of the Encapsulation Extended Community is when there are *no sub-TLVs*, other than the Address Family sub-TLV (item 3 in the list of conditions).
[Linda] That is our understanding as well. This document doesn’t specify additional sub-TLVs to be added to the BGP UPDATE with the Encapsulation Extended Community.

- In draft-ietf-idr-sdwan-edge-discovery-12 Section 6.3 we see the definition of the IPsec-SA-ID Sub-TLV of the SD-WAN-Hybrid tunnel type. This seems pretty central to the purpose of the spec. So, the SD-WAN-Hybrid tunnel type does have sub-TLVs in addition to the Address Family, and therefore MUST NOT be used in an Encapsulation Extended Community.
[Linda] All those sub-TLVs are NOT used with Encapsulation Extended Community. Those Sub-TLVs are under the Tunnel Encapsulation Path attribute in a separate UPDATE (U2 in the document) for SD-WAN edges to advertise the information about their WAN ports. There is no Encapsulation Extended Community included when an edge node advertises its WAN port information. Please see Section 5 for BGP Walk Through details.

- Also, in draft-ietf-idr-sdwan-edge-discovery-12 Section 5.1 we see that the client route update uses the Encapsulation Extended Community (emphasis added):

[Linda] The Client Route UPDATE can use the Extended Community to indicate that their associated tunnel information is advertised by separate UDPATE. The purpose is to reduce the size of the Clint Route UPDATE message size because the tunnel associated with IPsec has a lot of information to be exchanged. They don’t change at the same frequency as the Client Routes.
```
5.  Client Route UPDATE

   The SD-WAN network's Client Route UPDATE message is the same as the
   L3 VPN or EVPN client route UDPATE message.  The SD-WAN Client Route
   UPDATE message uses the **Encapsulation Extended Community** and the
   Color Extended Community to link with the SD-WAN Underlay UPDATE
   Message.
```

- It’s clear from other parts of the spec that the tunnel type is SD-WAN-Hybrid, for example, this is both stated in Section 3.3, and then used in the example (same section).
[Linda] The Client Route Update message is NOT using RFC9012. Here is to indicate that another type might be needed. As this is a BGP usage draft, with the intent to explain how to use BGP, with the justification to BGP extension later.

- But RFC 9012 §4.1 told us we can’t use a tunnel type with sub-TLVs as an Encapsulation Extended Community!
[Linda] The Client Route Update message is NOT using RFC9012.

I think what you really must be trying to do is use the Tunnel Encapsulation attribute (only!) to carry the SD-WAN-Hybrid in the SD-WAN Underlay route, and then have the client routes making use of that tunnel recurse into the underlay route (including tunnel) as per RFC 9012 Section 8. Note that Section 8 does NOT require that the client route carry the Encapsulation Extended Community — the next hop address is both necessary and sufficient to effectuate the linkage to the underlay route.
[Linda] You are correct. The Tunnel Encapsulation Attribute is used to carry the SD-WAN-Hybrid for SD-WAN edge nodes to advertise the WAN ports (i.e. the under route).



Thanks,

—John