Subject: Anycast SID for SRv6 Path Egress Protection?) draft-hu-rtgwg-srv6-egress-protection

From: Huaimo Chen <[email-masked]>
Date: Thu, 21 Nov 2019 08:47:19 +0000

Hi Shraddha,

    Thanks for your question about using anycast SID for SRv6 Path Egress Protection.

    There are a few issues on using anycast SID for SRv6 Path Egress Protection, which include:
    1) The (primary) egress (e.g., PE3 in the figure on page 2 presented in IETF 106) and the backup egress (e.g., PE4) need to be configured with the same locator and VPN SID.
    2) When the failure on the interface between the egress (e.g., PE3) and the CE (e.g., CE2) happens, the traffic may loop and get lost. The ingress (e.g., PE1) will send packets to the egress (e.g., PE3), which forwards the packets to the backup egress (e.g., PE4) through anycast SID. If the link cost between the egress (e.g., PE3) and the backup egress (e.g., PE4) is much bigger than others, the egress sends back the packets to P1, which sends the packets to the egress again (packets loop between P1 and PE3).
    3) BGP is unable to select its next hop, that is that whichever next hop (either PE3 or PE4) selected by BGP is overwritten by the IGP shortest path.

Best Regards,
Huaimo