Re: Header Insertion and TI-FA

[Gyan Mishra <[e-mail]>]

Hi Ron

I was thinking the same this past weekend as well.

So at the PLR node which could be any transit P router in the core.  So to
create that bypass transit path FRR link and node protection Next Next hop
(NNH) path around the  failed node or link, an EH header is inserted in
flight on the PLR node to the merge point PQ node for the bypass flow 50ms
failover.

So the agreement we came up with end of last year with Spring, is to add a
6in6 encapsulation along with EH insertion of the type 4 SRH header at the
PLR node to the merge point PQ node to be in compliance with RFC 8200.  The
additional encapsulation would in essence appear like the SRv6 source node
performing the encapsulation.

I looked in the PGM and SRH draft but I could not find the verbiage of the
update to add to additional 6in6 encapsulatio

So how would the packet look now?

IPv6 6in6 encapsulation- SR source node
EH SRH type 4 inserted (steering packet PGM)
IPv6 6in6 encapsulation - PLR node
EH SRH type 4 inserted ( steer to merge point PQ node)
Payload

At the merge point PQ node the EH SRH header is removed.

Packet is now steered via the original SRH header inserted at the SRv6
source node to the PSP node.

PSP pseudocode
SL== 1 ;  SL = SL -1 ; decrement pointer
Remove EH SRH header

Forward packet to USP egress PE end node.

USP egress PE endpoint SL=O

USD - remove 6in6 encapsulation
Send packet to IPv6 routing engine L3 vpn
End.x function processing


Spring - Please provide section within PGM that has the verbiage of the
6in6 encapsulation at the PLR node.

Thanks

Gyan

On Mon, May 11, 2020 at 8:57 AM Ron Bonica <rbonica=
[e-mail]> wrote:

> Folks,
>
>
>
> Happy Monday!
>
>
>
> As I was painting this weekend, I remembered that the use-case for IPv6
> Header insertion is TI-LFA. This made the following questions come to mind:
>
>
>
>    - How does TI-LFA work when the original packet already contains a
>    routing header? Will it insert a second, so that the packet has two routing
>    headers?
>    - How does TI-LFA work when the node directly upstream of the link
>    (i.e., the PLR) is not a segment endpoint? Will it insert an routing
>    header? Is that consistent with 8200?
>
>
>
>
>       Ron
>
>
>
>
>
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-- 

Gyan  Mishra

Network Engineering & Technology

Verizon

Silver Spring, MD 20904

Phone: [phone]

Email: [e-mail]