Hi Stanislav
I tried disabling zebra nexthop kernel enable in FRR (to avoid NHID-related
events), but VPP is still missing some RTM_DELROUTE events.
FRR logs confirm that RTM_DELROUTE messages are sent correctly for all routes,
but VPP does not receive/process all of them.
Could you please let me know which Linux kernel version you are using on your
setup?
Thanks.
Manoj
On Tuesday, December 23, 2025 at 11:19:56 PM GMT+5:30, Stanislav Zaikin via
lists.fd.io <[email protected]> wrote:
Hello Manoj,
You can try to disable nethops in zebra using this command "no zebra nexthop
kernel enable".
Another option is to support nhids in the LCP plugin. I added a couple of years
ago nhid support in libnl and also have somewhere a patch to vpp that makes
libnl an explicit external dependency with pinning to a specific version (in
case the system libnl is too old).
Also, I tried to integrate linux nexthops in lcp and miserably failed :) After
that I just switched to my custom control plane and didn't need those nhid
support anymore.
But maybe you can add this support if you want to. Contributions are welcomed.
On Mon, 22 Dec 2025 at 16:26, monu Sharma via lists.fd.io
<[email protected]> wrote:
Hi,
We are integrating VPP with FRR via netlink (RTM_NEWROUTE / RTM_DELROUTE) and
have observed an issue in VPP 24.10 regarding nexthop (NHID) delete handling.
Observation
When FRR withdraws BGP routes, Linux sometimes emits RTM_DELNEXTHOP events
(NHID delete) sometimes without corresponding RTM_DELROUTE messages.
Example netlink event observed:
RTNL NEXTHOP DELETE
nhid=1331 family=2 proto=zebra oif=12
gw=192.168.12.21
Routes referencing this NHID (e.g.):
192.168.0.0/24 nhid 1331 encap mpls 24021 via 192.168.12.21 dev ens6.1012 proto
bgp
are removed from the Linux kernel, but VPP does not delete the corresponding
FIB entry, since NHID delete events are currently not handled.
Impact
-
VPP FIB can retain stale routes
-
Leads to state mismatch between Linux kernel and VPP
-
Especially visible with FRR/Zebra + MPLS + nexthop objects
Expectation
When RTM_DELNEXTHOP is received:
-
VPP (or plugins consuming netlink) should invalidate and remove all routes
associated with the deleted NHID
-
Or at least provide a mechanism to track NHID → route mappings and act on NHID
deletion
Question
Is the lack of RTM_DELNEXTHOP handling a known limitation?
Are there plans to add native NHID tracking and cleanup in VPP, ? Any guidance
or recommended approach would be appreciated.
Please find ubuntu and kernel version.uname -aLinux -dev 5.15.0-101-generic
#111-Ubuntu SMP Tue Mar 5 20:16:58 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
dpkg -l | grep linux-imageii linux-image-5.15.0-101-generic 5.15.0-101.111
amd64 Signed kernel image genericpi
linux-image-5.15.0-97-generic 5.15.0-97.107 amd64
Signed kernel image genericcat /etc/os-releasePRETTY_NAME="Ubuntu 22.04.3
LTS"NAME="Ubuntu"VERSION_ID="22.04"VERSION="22.04.3 LTS (Jammy
Jellyfish)"VERSION_CODENAME=jammyID=ubuntuID_LIKE=debianHOME_URL="https://www.ubuntu.com/"SUPPORT_URL="https://help.ubuntu.com/"BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"UBUNTU_CODENAME=jammy
Thanks & regards,
Manoj
--
Best regards
Stanislav Zaikin
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