Re: [PATCH net-next 4/4] bonding: balance ICMP echoes in layer3+4 mode

[Matteo Croce]

On Wed, Oct 23, 2019 at 12:01 PM Simon Horman
<simon.horman@xxxxxxxxxxxxx> wrote:
>
> On Mon, Oct 21, 2019 at 10:09:48PM +0200, Matteo Croce wrote:
> > The bonding uses the L4 ports to balance flows between slaves.
> > As the ICMP protocol has no ports, those packets are sent all to the
> > same device:
> >
> >     # tcpdump -qltnni veth0 ip |sed 's/^/0: /' &
> >     # tcpdump -qltnni veth1 ip |sed 's/^/1: /' &
> >     # ping -qc1 192.168.0.2
> >     1: IP 192.168.0.1 > 192.168.0.2: ICMP echo request, id 315, seq 1, length 64
> >     1: IP 192.168.0.2 > 192.168.0.1: ICMP echo reply, id 315, seq 1, length 64
> >     # ping -qc1 192.168.0.2
> >     1: IP 192.168.0.1 > 192.168.0.2: ICMP echo request, id 316, seq 1, length 64
> >     1: IP 192.168.0.2 > 192.168.0.1: ICMP echo reply, id 316, seq 1, length 64
> >     # ping -qc1 192.168.0.2
> >     1: IP 192.168.0.1 > 192.168.0.2: ICMP echo request, id 317, seq 1, length 64
> >     1: IP 192.168.0.2 > 192.168.0.1: ICMP echo reply, id 317, seq 1, length 64
> >
> > But some ICMP packets have an Identifier field which is
> > used to match packets within sessions, let's use this value in the hash
> > function to balance these packets between bond slaves:
> >
> >     # ping -qc1 192.168.0.2
> >     0: IP 192.168.0.1 > 192.168.0.2: ICMP echo request, id 303, seq 1, length 64
> >     0: IP 192.168.0.2 > 192.168.0.1: ICMP echo reply, id 303, seq 1, length 64
> >     # ping -qc1 192.168.0.2
> >     1: IP 192.168.0.1 > 192.168.0.2: ICMP echo request, id 304, seq 1, length 64
> >     1: IP 192.168.0.2 > 192.168.0.1: ICMP echo reply, id 304, seq 1, length 64
> >
> > Signed-off-by: Matteo Croce <mcroce@xxxxxxxxxx>
>
> I see where this patch is going but it is unclear to me what problem it is
> solving. I would expect ICMP traffic to be low volume and thus able to be
> handled by a single lower-device of a bond.
>
> ...

Hi,

The problem is not balancing the volume, even if it could increase due
to IoT devices pinging some well known DNS servers to check for
connection.
If a bonding slave is down, people using pings to check for
connectivity could fail to detect a broken link if all the packets are
sent to the alive link.
Anyway, although I didn't measure it, the computational overhead of
this changeset should be minimal, and only affect ICMP packets when
the ICMP dissector is used.

Regards,
-- 
Matteo Croce
per aspera ad upstream