Hi Yingzhen：
Thanks for your comments, please see inline.
Thanks
Zhibo
From: rtgwg [mailto:[email protected]] On Behalf Of Yingzhen Qu
Sent: Saturday, August 5, 2023 9:00 AM
To: [email protected]; RTGWG
<[email protected]>
Subject: Questions about draft-cheng-rtgwg-srv6-multihome-egress-protection
Hi Authors,
(as individual contributor)
I reviewed the draft, and have the following questions:
1.
About PSD definition, in section 3.2, there are the following texts:
" A penultimate SRv6 Segment Endpoint node is one that, as part of the
SID processing, copies the last SID from the SRH into the IPv6
Destination Address and decrements the Segments Left value from one
to zero.
"
" The PSD operation only takes place at the egress node and does not
happen at any transit node. When a SID of PSD flavor is processed at
a transit node, the PSD behavior is not performed as described in
the pseudocode below since Segments Left would not be 1 or 0.
"
so to my understanding, P2 is the penultimate endpoint in the example in Figure
1, correct? however there is "PSD-flavored SID" on PE3. Please clarify.
[Zhibo] Yes, your understanding is correct. We will modify the description in
the next version to avoid ambiguity.
2.
In Section 4, "After the configuration, PE1 determines that PE3's backup SID
is PE4's VPN SID through the routing optimization strategy of BGP." . Can you
please elaborate how PE1 decides PE4 to be the backup SID? What if the path for
P2 to reach PE4 is P2->PE3->PE4?
[Zhibo] According to the BGP route selection principle, the ingress PE node
selects the preferred route as the primary node and the second-best route as
the backup node.
After egress protection is enabled, if PE3 fails, P2 forwards traffic to PE4.
If PE3 is the next hop of P2, P2 will forwards traffic to PE4 through the
TI-LFA backup path. This solution does not affect the implementation of this
solution.
3.
In section 3.4, it mentions that P2 could be several hops away from the egress
node. In this case, if PE3 fails, how does P2 detect the failure of PE3
quickly? What if a link between P2 and PE3 fails?
[Zhibo]
P2 detect the failure of PE3 via:
• IGP convergence
• BFD detection
Traditional FRR also maximizes the protection scope and preferentially
considers node faults without distinguishing whether a link fault or node fault
occurs.
Thanks,
Yingzhen
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