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Bug#1101876: /bin/ip: disappearing permanent arp entries

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  Bug#1101876: /bin/ip: disappearing permanent arp entries Piotr Dzierzak <dzierzak.piotr@gmail.com> - 2025-04-01 20:00 +0200
    Bug#1101876: /bin/ip: disappearing permanent arp entries Daniel Gröber <dxld@darkboxed.org> - 2025-04-01 20:40 +0200
    Bug#1101876: disappearing permanent arp entries Piotr Dzierżak <dzierzak.piotr@gmail.com> - 2025-05-05 12:10 +0200

#86703 — Bug#1101876: /bin/ip: disappearing permanent arp entries

Package: iproute2
Version: 6.1.0-3
Severity: important
File: /bin/ip
X-Debbugs-Cc: dzierzak.piotr@gmail.com

Dear Maintainer,

I have a router on Debian 12. The static / permanent arp entries are disappearing in the system :/

-- System Information:
Debian Release: 12.10
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.12.12+bpo-amd64 (SMP w/2 CPU threads; PREEMPT)
Locale: LANG=pl_PL.UTF-8, LC_CTYPE=pl_PL.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages iproute2 depends on:
ii  debconf [debconf-2.0]  1.5.82
ii  libbpf1                1:1.1.0-1
ii  libbsd0                0.11.7-2
ii  libc6                  2.36-9+deb12u10
ii  libcap2                1:2.66-4
ii  libcap2-bin            1:2.66-4
ii  libdb5.3               5.3.28+dfsg2-1
ii  libelf1                0.188-2.1
ii  libmnl0                1.0.4-3
ii  libselinux1            3.4-1+b6
ii  libtirpc3              1.3.3+ds-1
ii  libxtables12           1.8.9-2

Versions of packages iproute2 recommends:
pn  libatm1  <none>

Versions of packages iproute2 suggests:
pn  iproute2-doc  <none>
ii  python3       3.11.2-1+b1

-- debconf information:
  iproute2/setcaps: false

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#86704

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Hi Piotr,

On Tue, Apr 01, 2025 at 07:51:07PM +0200, Piotr Dzierzak wrote:
> I have a router on Debian 12. The static / permanent arp entries are
> disappearing in the system :/

This report is not very specific :-). Could you give me some more details
on what these ARP entries look like exactly i.e. show the command/config
you use to create them?

I'd also recommend watching ip-monitor(8) to firgure out when this is
happening exactly. Something like:

    $ stdbuf -oL ip -t monitor all | tee /tmp/ipmon.log

or alternatively you can dump the raw kernel events into a file using
rtmon(8) and print them later:

   $ rtmon file /tmp/rtmon.log
   [...]
   $ ip monitor file /tmp/rtmon.log

IIRC even the raw rtmon dump doesn't contain the PID of the process making
the change but we should be able to correlate the removal with what else is
going on.

Please attach an event dump in one of those formats. Beware: The files will
be public in the Debian BTS. Send it to me directly if you don't like
sharing your IP(s) publically.

--Daniel

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#87366 — Bug#1101876: disappearing permanent arp entries

I have changed DHCP server from dnsmasq to kea. Now the static arp 
entries are persistent :)

So maybe there is a bug in the dnsmasq.

Best regards
Piotr

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