Re: Can one Destination Address appear in both Tunnel Encap Attribute and in MP_REACH_NLRI ?

Srihari and Robert,

Thank you very much for the discussion.

Your explanation indicates that the tunnel information described in Tunnel Path Attributes are applicable to all the NLRI listed in the MP-NLRI Path Attributes, correct?
For example, D1/D2/D3/D4 all have R2 as Next Hop, and R2 supports GRE and VxLAN.  The Update from R2 will have D1, D2, D3, D4 listed in the MP-NLRI (code= 14), and GRE tunnel & VxLAN tunnel listed under the Tunnel Attribute (code = 23).

When R1 receives the UPDATE from R2, R1 can assume that packets to D1, D2, D3, D4 can use either VxLAN or GRE. Is it correct?

So if R2 needs to specifically indicate GRE for D1, VxLAN for D2, D3, and IPinIP for D4, then R2 needs to send 3 separate UPDATE messages. Is it correct?

Thank you very much.



From: Srihari Sangli <[email protected]>
Sent: Thursday, October 17, 2019 3:08 AM
To: Robert Raszuk <[email protected]>; Srihari Sangli <[email protected]>
Cc: Linda Dunbar <[email protected]>; [email protected]; [email protected]
Subject: Re: [Idr] Can one Destination Address appear in both Tunnel Encap Attribute and in MP_REACH_NLRI ?

Hi Robert,



My reading of Linda's point was a question regarding the case where for prefix A NLRI points to
next hop NH_1 but tunnel endpoint says go to NH_2.

Is such update still valid ?

Has tunnel encapsulation attribute power to "overrule" BGP next hop from MP_REACH ?


The draft in Section 5 explains this. If the update has a valid Tunnel Encapsulation attribute and if any of the tunnel(s) is considered to be feasible, then it MUST use the tunnel. That means in your example, such an update is valid and NH_2 should be used.

Hope this helps. Thanks.

srihari…

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