SRv6 BGP SID reachability #14810

dmytroshytyi-6WIND · 2023-11-16T14:54:27Z

For BGP SRv6 updates, This PR considers "SRv6 SID reachability" and replaces the NH reachability with the
SRv6 SID reachability.

Today, only the NH reachability is checked, and when route is installed, if the SRv6 SID is not reachable
then the SRv6 segs route will fail to be installed.
This is what happens on kernel.

This PR:

avoids this use case, and does not install the BGP route.
ensures the SID is reachable, before installing the BGP route to zebra

Possible cases like the one below are not considered, and do not work anyway:

Router A and D are running BGP protocol. The route map, to set nexthop == C, is configured on
router D. Such that router C IPv6 address is verified to be reachable to flag the SRv6 reachable,
but if route on the router C that points to D router's SRv6 SID dissapears(broken link),
on node A SID is expected to be still reachable, because nexthop C is reachable.

BGP update with explicit nexthop(C) set via route-map and SRV6 SID
__________________________ 
|                         |
▽                         ^
(A-B-C--------------------D)
     
     ^                    ^
nexthop C                SRv6 SID
of BGP update

doc/user/bgp.rst

bgpd/bgp_nht.c

tests/topotests/bgp_srv6_sid_reachability/r1/bgpd.conf

tests/topotests/bgp_srv6_sid_reachability/r2/bgpd.conf

tests/topotests/bgp_srv6_sid_reachability/r3/bgpd.conf

ton31337 · 2023-11-19T18:54:38Z

Just a quick question: is this behavior something that other vendors have (SID reachability tracking)? I'm worried that we can't break anything if this is turned ON by default and can't be controlled. Maybe a knob would be handy?

riw777

looks good

bgpd/bgp_nht.c

eddieruan-alibaba · 2023-11-30T22:39:47Z

Would this raise any scale concerns?

VPN SID is similar to vpn label for MPLS VPN, which provides local information once packets reach to this PE. In the example you provide,

| |
▽ ^
(A-B-C--------------------D)

If we don't sue route-map to set nexthop, the nexthop is D. Do we really want to let A, B, C all aware the reachablity of your VPN SID, or just keep it as local context to D if some chip has scale concerns with v6 prefixes.

https://datatracker.ietf.org/doc/rfc8986/ section 3.3. "Routed and non-routed SRv6 SIDs are the SRv6 instantiation of
global and local segments, "

how do you plan to handle these local segment use cases?

pguibert6WIND · 2024-01-19T11:23:46Z

ci:rerun

cscarpitta

@dmytroshytyi-6WIND Thanks for the SRv6 contribution. Overall LGTM, I have only two nits.

tests/topotests/bgp_srv6_sid_reachability/test_bgp_srv6l3vpn_over_ipv6.py

pguibert6WIND · 2024-01-26T12:20:52Z

bgpd/bgp_nht.c

-
-		if (is_bgp_static) {
+		if (pi && pi->attr && pi->attr->srv6_l3vpn) {
+			IPV6_ADDR_COPY(&(p->u.prefix6),


no need to check for pi != NULL. it is alread done above.

Thanks fixed.

pguibert6WIND · 2024-01-26T12:22:00Z

bgpd/bgp_nht.c

@@ -660,6 +672,7 @@ static void bgp_process_nexthop_update(struct bgp_nexthop_cache *bnc,

 			if (BGP_DEBUG(nht, NHT)) {
 				char buf[NEXTHOP_STRLEN];
+
 				zlog_debug(


no need to add empty line

Thanks Fixed.

pguibert6WIND

2 minor issues.
also, the commit "bgpd: srv6 sid reachability information".
I would add this in the commit log:
Fixes 7f8c7d9 ("bgpd: ignore nexthop validation for srv6-vpn")

BGP IPv4 L3VPN with SRv6 SID reachability example provided in the documentation Signed-off-by: Dmytro Shytyi <[email protected]>

Enable the SRv6 SID prefix generation in make_prefix() function of bgp_nht.c. Signed-off-by: Dmytro Shytyi <[email protected]> fixup: bgpd: extend make_prefix to form srv6-based prefix

In the case of SRv6-VPN we track the reachability to the SID. We check that the SID is available in the BGP update and then we check the nexthop reachability. Fixes 7f8c7d9 ("bgpd: ignore nexthop validation for srv6-vpn") Signed-off-by: Dmytro Shytyi <[email protected]> Signed-off-by: Philippe Guibert <[email protected]>

Verify that SRv6 SID becomes unreachable and further the IPv4 route in L3VPN becomes invalid. Signed-off-by: Dmytro Shytyi <[email protected]>

dmytroshytyi-6WIND · 2024-01-30T16:51:38Z

ci:rerun

dmytroshytyi-6WIND · 2024-01-31T06:28:26Z

ci:rerun

riw777 · 2024-02-20T14:57:58Z

2 minor issues. also, the commit "bgpd: srv6 sid reachability information". I would add this in the commit log: Fixes 7f8c7d9 ("bgpd: ignore nexthop validation for srv6-vpn")

If this were in, I think we could merge this.

dmytroshytyi-6WIND · 2024-02-20T15:53:54Z

2 minor issues. also, the commit "bgpd: srv6 sid reachability information". I would add this in the commit log: Fixes 7f8c7d9 ("bgpd: ignore nexthop validation for srv6-vpn")

If this were in, I think we could merge this.

This commit log includes the "Fixes" tag:
b3ac502

And these two comments were addressed:
#14810 (comment)
#14810 (comment)

riw777

looks good

This commit brings PR FRRouting/frr#14810 from FRR mainline to SONiC SRv6 BGP SID reachability FRRouting/frr#14810 Signed-off-by: cscarpitta <[email protected]>

frrbot bot added bgp documentation tests Topotests, make check, etc labels Nov 16, 2023

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dmytroshytyi-6WIND force-pushed the srv6_bgp_sid_reachability branch 2 times, most recently from ebfc5be to 4086473 Compare January 25, 2024 15:00

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dmytroshytyi-6WIND added 4 commits January 30, 2024 16:13

doc: bgp ipv4 l3vpn sid reachability

f49fc76

BGP IPv4 L3VPN with SRv6 SID reachability example provided in the documentation Signed-off-by: Dmytro Shytyi <[email protected]>

bgpd: extend make_prefix to form srv6-based prefix

26c747e

Enable the SRv6 SID prefix generation in make_prefix() function of bgp_nht.c. Signed-off-by: Dmytro Shytyi <[email protected]> fixup: bgpd: extend make_prefix to form srv6-based prefix

tests: an srv6 sid reachability use-case

5101463

Verify that SRv6 SID becomes unreachable and further the IPv4 route in L3VPN becomes invalid. Signed-off-by: Dmytro Shytyi <[email protected]>

dmytroshytyi-6WIND force-pushed the srv6_bgp_sid_reachability branch from 4086473 to 5101463 Compare January 30, 2024 15:17

riw777 approved these changes Feb 27, 2024

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riw777 merged commit c4f9b87 into FRRouting:master Feb 27, 2024
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cscarpitta mentioned this pull request Dec 16, 2024

[FRR]: Add support for SRv6 SID Manager sonic-net/sonic-buildimage#21185

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SRv6 BGP SID reachability #14810

SRv6 BGP SID reachability #14810

dmytroshytyi-6WIND commented Nov 16, 2023

ton31337 commented Nov 19, 2023

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eddieruan-alibaba commented Nov 30, 2023

pguibert6WIND commented Jan 19, 2024

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SRv6 BGP SID reachability #14810

SRv6 BGP SID reachability #14810

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