Hi Pim, > Quick followup, when I downgraded to 25.10-rc0~246-g49f6ec0c2 ARP > flooding stopped. Perhaps there is a regression between > 25.10-rc0~246-g49f6ec0c2 and 25.10.0
I could not find commit 49f6ec0c2, do you have specific commits in addition to the upstream VPP? I looked at commits between 25.10-rc0 and 25.10.0 and I could only see [1] and [2] that could have impacted ARP behavior, although I can't see how they could introduce a regression, but maybe you can try reverting those and see what happens. Otherwise your best bet might be to do a git bisect :/ [1] https://gerrit.fd.io/r/c/vpp/+/43045 [2] https://gerrit.fd.io/r/c/vpp/+/43589 best ben On 28.11.2025 23:04, Pim van Pelt via lists.fd.io wrote: > Hoi, > > I know this is a long shot, but this afternoon I upgraded one of my > routers at AS50869 from VPP 24.10 to VPP 25.10.0 (with the LinuxCP fix). > Shortly there-after, two internet exchanges (both with a /23 > peeringlan) complained that the router was flooding ARP requests. > I could not see these in Linux CP, but they were visible in the > Internet Exchange when looking at a packet dump. > I could however see the ARP replies from the folks my router was > flooding, like so: > > root@nlams0:/etc/bird/ebgp/groups# time tcpdump -evni speedix arp > 16:08:46.638960 44:4c:a8:c7:4a:33 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.223.39 is-at 44:4c:a8:c7:4a:33, length 46 > 16:08:46.881844 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:46.886507 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:46.902967 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:46.905873 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:46.940812 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:46.973942 44:4c:a8:c7:4a:33 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.223.39 is-at 44:4c:a8:c7:4a:33, length 46 > 16:08:46.983844 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.003539 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.010575 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.030974 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.069999 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.123048 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.134061 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.158991 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > 16:08:47.159000 c4:ca:2b:69:c8:f7 > b8:59:9f:e2:0a:9f, ethertype ARP > (0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Reply > 185.1.222.21 is-at c4:ca:2b:69:c8:f7, length 46 > > In this network, the VPP router is b8:59:9f:e2:0a:9f and the router > that was being flooded is at c4:ca:2b:69:c8:f7. They saw the traffic > also. It immediately stopped when I set a static neighbor entry in > Linux. I took a trace from dpdk-input but it did not reveal any > outbound ARP traffic (which makes sense). It did however show the ARP > replies. > > Could it be that between 24.10 and 25.10 release, something changed in > the ARP handling that might trigger an ARP flood from within arp > request/reply/ip-neighbor code? I'm hoping somebody can remember any > changes, I scanned over a bunch of changes but a year is a long time > and bisecting on an internet exchange is impractical. I may be able to > repro this behavior in a lab, but before I go deeper: does this ARP > flooding ring a bell for anybody ? > > groet, > Pim > > > > -- Pim van Pelt <[email protected]> PBVP1-RIPE https://ipng.ch/
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