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These tests generate various IPv6 flows, encapsulate them in GRE packets and check that the encapsulated packets are distributed between the available nexthops according to the configured weights. Unlike the corresponding IPv4 tests, these tests sometimes fail in the netdev CI because of large discrepancies between the expected and measured ratios [1]. This can be explained by the fact that the IPv4 tests generate about 3,600 different flows whereas the IPv6 tests only generate about 784 different flows (potentially by mistake). Fix by aligning the IPv6 tests to the IPv4 ones and increase the number of generated flows. [1] [...] # TEST: ping [ OK ] # INFO: Running IPv6 over GRE over IPv4 multipath tests # TEST: ECMP [FAIL] # Too large discrepancy between expected and measured ratios # INFO: Expected ratio 1.00 Measured ratio 1.18 [...] Signed-off-by: Ido Schimmel <idosch@nvidia.com> Link: https://lore.kernel.org/r/20240304095612.462900-7-idosch@nvidia.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Motivation
==========
One of the nice things about network namespaces is that they allow one
to easily create and test complex environments.
Unfortunately, these namespaces can not be used with actual switching
ASICs, as their ports can not be migrated to other network namespaces
(NETIF_F_NETNS_LOCAL) and most of them probably do not support the
L1-separation provided by namespaces.
However, a similar kind of flexibility can be achieved by using VRFs and
by looping the switch ports together. For example:
br0
+
vrf-h1 | vrf-h2
+ +---+----+ +
| | | |
192.0.2.1/24 + + + + 192.0.2.2/24
swp1 swp2 swp3 swp4
+ + + +
| | | |
+--------+ +--------+
The VRFs act as lightweight namespaces representing hosts connected to
the switch.
This approach for testing switch ASICs has several advantages over the
traditional method that requires multiple physical machines, to name a
few:
1. Only the device under test (DUT) is being tested without noise from
other system.
2. Ability to easily provision complex topologies. Testing bridging
between 4-ports LAGs or 8-way ECMP requires many physical links that are
not always available. With the VRF-based approach one merely needs to
loopback more ports.
These tests are written with switch ASICs in mind, but they can be run
on any Linux box using veth pairs to emulate physical loopbacks.
Guidelines for Writing Tests
============================
o Where possible, reuse an existing topology for different tests instead
of recreating the same topology.
o Tests that use anything but the most trivial topologies should include
an ASCII art showing the topology.
o Where possible, IPv6 and IPv4 addresses shall conform to RFC 3849 and
RFC 5737, respectively.
o Where possible, tests shall be written so that they can be reused by
multiple topologies and added to lib.sh.
o Checks shall be added to lib.sh for any external dependencies.
o Code shall be checked using ShellCheck [1] prior to submission.
1. https://www.shellcheck.net/