Validating multi-path in production?

Sun Nov 14 11:29:25 UTC 2021

On Fri, 12 Nov 2021 at 16:54, Adam Thompson <athompson at merlin.mb.ca> wrote:

> The best I've come up with so far is to have two test systems (typically
> VMs) that use adjacent IP addresses and adjacent MAC addresses, and test
> both inbound and outbound to/from those, blindly trusting/hoping that
> hashing algorithms will *probably* exercise both paths.
>

If the goal is to test that traffic *is* being distributed across multiple
links based on traffic headers, then you can definable roll your own. I
think the problem is orchestrating it (feeding your topology data into the
tool, running the tool, getting the results out, and interpreting the
results etc).

A coupe of public examples:
https://github.com/facebookarchive/UdpPinger
https://www.youtube.com/watch?v=PN-4JKjCAT0

If you do roll your own, you need to taylor the tests to your topology and
your equipment. For example, you can have two VMs as you mentioned, each at
opposite ends of the network. Then, if your network uses a 5-tuple for ECMP
inside the core for example, you could send many flows between the two VMs,
rotating the sauce port for example, to ensure all links in a LAG or all
ECMP paths are used.

It's tricky to know the hashing algo for every type of device you have in
your network, and for each traffic type for each device type, if you have a
multi vendor network. Also, if your network carries a mix of IPv4, IPv6,
PPP, MPLS L3 VPNs, MPLS L2 VPNs, GRE, GTP, IPSEC, etc. The number of
permutations of tests you need to run and the result sets you need to
parse, grows very rapidly.

Cheers,
James.
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