Re: Does the debian kernel sends the gratuitous arp ?

[Jeffrey Walton <noloader@gmail.com>]

On Sat, Oct 7, 2023 at 1:38 AM <tomas@tuxteam.de> wrote:
>
> On Fri, Oct 06, 2023 at 05:20:22PM -0400, Jeffrey Walton wrote:
> > On Fri, Oct 6, 2023 at 2:04 PM Balaji G <gbalajieie@gmail.com> wrote:
> > >
> > > Hi,
> > >     I am using "Debian GNU/Linux 11 (bullseye)" with kernel version 5.16.12.
> > > When i do a link up/down i don't see any Gratuitous ARP being sent.
> > >
> > > # echo 1 > /proc/sys/net/ipv4/conf/eno5np0/arp_notify
> > > # ip link set down dev eno5np0
> > > # ip link set up dev eno5np0
> > >
> > > Captured all the packets via tcpdump & the tcpdump is not showing any Gratuitous ARP packets.
> > >
> > > But, with the same commands i could see the Gratuitous ARP being sent in Red hat.9.0 (Plow).
> > > So, please let me know if this is a specific scenario in Debian 11 ??
> >
> > I think that's now Poettering:
> > https://github.com/systemd/systemd/blob/main/src/libsystemd-network/sd-ipv4acd.c#L302
>
> As  Geert says, probably it needs an ip address to be able to send
> an ARP. Perhaps the Redhat box has one set by default?

OP asked if this was specific to Red Hat. The answer is No, it is
baked into Systemd nowadays.

> What does "ip addr show dev xxxx" say?

I have no idea.

Jeff