Re: Does the debian kernel sends the gratuitous arp ?

[Geert Stappers <stappers@debian.org>]

On Fri, Oct 06, 2023 at 09:19:32PM +0200, Geert Stappers wrote:
> On Fri, Oct 06, 2023 at 05:52:16PM +0530, Balaji G 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.
> 
> ARP

Address Resolution Protocol

  
> > # echo 1 > /proc/sys/net/ipv4/conf/eno5np0/arp_notify
> 
> Probably transmitted "I tried to enforce ARP notification"
> 
> 
> > # ip link set down dev eno5np0
> > # ip link set up dev eno5np0
> 
> link

As in "the link layer"
  
 
> > Captured all the packets via tcpdump & the tcpdump is not showing any
> > Gratuitous ARP packets.
> 
> Why should it?     (Yes, that is a serious question.)
 
As opening question for further discussion.

Because I like the question
  Does the Debian kernel sends the gratuitous ARP ?

I think the answer is   YES
and I very curious when gratuitous ARP is ommitted.

  
> > But, with the same commands i could see the Gratuitous ARP being sent in
> > Red hat.9.0 (Plow).
> 
> I think more factors have been change as kernel.
 
As invitation for telling how the comparsion was done.


> > So, please let me know if this is a specific scenario in Debian 11 ??
> 
> I state that the OP, Original Poster, is the specific scenario.
> Yeah, that is a blunt statement.  Now hear me out.
> 
> Gratuitous ARP is "linking" MAC-address and  IP-address.
> 
> During `ip link set down dev eno5np0` and `ip link set up dev eno5np0`
> are NO IP-addresses involved.
> 
> So there is no need for ARP.
> 
> 
> I do hope to see a follow-up message like:
> 
>    Re-did the test with a static IP-address on the interface
>    and indeed see a gratuitous ARP
> 
> or some thing like
> 
>    To reproduce the missing gratuitous ARP do ...
> 
> Yeah, that might reveal more information about dev eno5np0.
> 
>  
> > Thanks,
> > Balaji
> 
> Groeten
> Geert Stappers

Because in https://lists.debian.org/debian-user/2023/10/msg00212.html I
wrote "Lets follow-up
https://lists.debian.org/debian-user/2023/10/msg00181.html "


Groeten
Geert Stappers
-- 
Silence is hard to parse