Re: [PATCH net-next v2 4/4] bonding: balance ICMP echoes in layer3+4 mode

[Nikolay Aleksandrov <nikolay@cumulusnetworks.com>]

On 29/10/2019 15:50, 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
> 
> Aso, let's use a flow_dissector_key which defines FLOW_DISSECTOR_KEY_ICMP,

Also ?

> so we can balance pings encapsulated in a tunnel when using mode encap3+4:
> 
>     # ping -q 192.168.1.2 -c1
>     0: IP 192.168.0.1 > 192.168.0.2: GREv0, length 102: IP 192.168.1.1 > 192.168.1.2: ICMP echo request, id 585, seq 1, length 64
>     0: IP 192.168.0.2 > 192.168.0.1: GREv0, length 102: IP 192.168.1.2 > 192.168.1.1: ICMP echo reply, id 585, seq 1, length 64
>     # ping -q 192.168.1.2 -c1
>     1: IP 192.168.0.1 > 192.168.0.2: GREv0, length 102: IP 192.168.1.1 > 192.168.1.2: ICMP echo request, id 586, seq 1, length 64
>     1: IP 192.168.0.2 > 192.168.0.1: GREv0, length 102: IP 192.168.1.2 > 192.168.1.1: ICMP echo reply, id 586, seq 1, length 64
> 
> Signed-off-by: Matteo Croce <mcroce@redhat.com>
> ---
>  drivers/net/bonding/bond_main.c | 77 ++++++++++++++++++++++++++++++---
>  1 file changed, 70 insertions(+), 7 deletions(-)
> 

Hi Matteo,
Wouldn't it be more useful and simpler to use some field to choose the slave (override the hash
completely) in a deterministic way from user-space ?
For example the mark can be interpreted as a slave id in the bonding (should be
optional, to avoid breaking existing setups). ping already supports -m and
anything else can set it, this way it can be used to do monitoring for a specific
slave with any protocol and would be a much simpler change.
User-space can then implement any logic for the monitoring case and as a minor bonus
can monitor the slaves in parallel. And the opposite as well - if people don't want
these balanced for some reason, they wouldn't enable it.

Or maybe I've misunderstood why this change is needed. :)
It would actually be nice to include the use-case which brought this on
in the commit message.

Cheers,
 Nik