xref: /linux/tools/testing/selftests/net/forwarding/README (revision 9410645520e9b820069761f3450ef6661418e279) 
1Motivation
2==========
3
4One of the nice things about network namespaces is that they allow one
5to easily create and test complex environments.
6
7Unfortunately, these namespaces can not be used with actual switching
8ASICs, as their ports can not be migrated to other network namespaces
9(dev->netns_local) and most of them probably do not support the
10L1-separation provided by namespaces.
11
12However, a similar kind of flexibility can be achieved by using VRFs and
13by looping the switch ports together. For example:
14
15                             br0
16                              +
17               vrf-h1         |           vrf-h2
18                 +        +---+----+        +
19                 |        |        |        |
20    192.0.2.1/24 +        +        +        + 192.0.2.2/24
21               swp1     swp2     swp3     swp4
22                 +        +        +        +
23                 |        |        |        |
24                 +--------+        +--------+
25
26The VRFs act as lightweight namespaces representing hosts connected to
27the switch.
28
29This approach for testing switch ASICs has several advantages over the
30traditional method that requires multiple physical machines, to name a
31few:
32
331. Only the device under test (DUT) is being tested without noise from
34other system.
35
362. Ability to easily provision complex topologies. Testing bridging
37between 4-ports LAGs or 8-way ECMP requires many physical links that are
38not always available. With the VRF-based approach one merely needs to
39loopback more ports.
40
41These tests are written with switch ASICs in mind, but they can be run
42on any Linux box using veth pairs to emulate physical loopbacks.
43
44Guidelines for Writing Tests
45============================
46
47o Where possible, reuse an existing topology for different tests instead
48  of recreating the same topology.
49o Tests that use anything but the most trivial topologies should include
50  an ASCII art showing the topology.
51o Where possible, IPv6 and IPv4 addresses shall conform to RFC 3849 and
52  RFC 5737, respectively.
53o Where possible, tests shall be written so that they can be reused by
54  multiple topologies and added to lib.sh.
55o Checks shall be added to lib.sh for any external dependencies.
56o Code shall be checked using ShellCheck [1] prior to submission.
57
581. https://www.shellcheck.net/
59
60Customization
61=============
62
63The forwarding selftests framework uses a number of variables that
64influence its behavior and tools it invokes, and how it invokes them, in
65various ways. A number of these variables can be overridden. The way these
66overridable variables are specified is typically one of the following two
67syntaxes:
68
69	: "${VARIABLE:=default_value}"
70	VARIABLE=${VARIABLE:=default_value}
71
72Any of these variables can be overridden. Notably net/forwarding/lib.sh and
73net/lib.sh contain a number of overridable variables.
74
75One way of overriding these variables is through the environment:
76
77	PAUSE_ON_FAIL=yes ./some_test.sh
78
79The variable NETIFS is special. Since it is an array variable, there is no
80way to pass it through the environment. Its value can instead be given as
81consecutive arguments to the selftest:
82
83	./some_test.sh swp{1..8}
84
85A way to customize variables in a persistent fashion is to create a file
86named forwarding.config in this directory. lib.sh sources the file if
87present, so it can contain any shell code. Typically it will contain
88assignments of variables whose value should be overridden.
89
90forwarding.config.sample is available in the directory as an example of
91how forwarding.config might look.
92