zebra: fix nhg out of sync between zebra and kernel (backport #14080) #15363
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PR#13413 introduces reinstall mechanism, but there is problem with the route
leak scenario.
With route leak configuration: ( `x1` and `x2` are binded to `vrf1` )
```
vrf vrf2
ip route 75.75.75.75/32 77.75.1.75 nexthop-vrf vrf1
ip route 75.75.75.75/32 77.75.2.75 nexthop-vrf vrf1
exit-vrf
```
Firstly, all are ok. But after `x1` is set down and up ( The interval
between the down and up operations should be less than 180 seconds. ) ,
`x1` is lost from the nexthop group:
```
anlan# ip nexthop
id 121 group 122/123 proto zebra
id 122 via 77.75.1.75 dev x1 scope link proto zebra
id 123 via 77.75.2.75 dev x2 scope link proto zebra
anlan# ip route show table 2
75.75.75.75 nhid 121 proto 196 metric 20
nexthop via 77.75.1.75 dev x1 weight 1
nexthop via 77.75.2.75 dev x2 weight 1
anlan# ip link set dev x1 down
anlan# ip link set dev x1 up
anlan# ip route show table 2 <- Wrong, one nexthop lost from group
75.75.75.75 nhid 121 via 77.75.2.75 dev x2 proto 196 metric 20
anlan# ip nexthop
id 121 group 123 proto zebra
id 122 via 77.75.1.75 dev x1 scope link proto zebra
id 123 via 77.75.2.75 dev x2 scope link proto zebra
anlan# show ip route vrf vrf2 <- Still ok
VRF vrf2:
S>* 75.75.75.75/32 [1/0] via 77.75.1.75, x1 (vrf vrf1), weight 1, 00:00:05
* via 77.75.2.75, x2 (vrf vrf1), weight 1, 00:00:05
```
From the impact on kernel:
The `nh->type` of `id 122` is *always* `NEXTHOP_TYPE_IPV4` in the route leak
case. Then, `nexthop_is_ifindex_type()` introduced by commit `5bb877` always
returns `false`, so its dependents can't be reinstalled. After `x1` is down,
there is only `id 123` in the group of `id 121`. So, Finally `id 121` remains
unchanged after `x1` is up, i.e., `id 122` is not added to the group even it is
reinstalled itself.
From the impact on zebra:
The `show ip route vrf vrf2` is still ok because the `id`s are reused/reinstalled
successfully within 180 seconds after `x1` is down and up. The group of `id 121`
is with old `NEXTHOP_GROUP_INSTALLED` flag, and it is still the group of `id 122`
and `id 123` as before.
In this way, kernel and zebra have become out of sync.
The `nh->type` of `id 122` should be adjusted to `NEXTHOP_TYPE_IPV4_IFINDEX`
after nexthop resolved. This commit is for doing this to make that reinstall
mechanism work.
Signed-off-by: anlan_cs <[email protected]>
(cherry picked from commit 045df14)
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