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_immutable) 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 60Cleanups 61-------- 62 63o lib.sh brings in defer.sh (by way of ../lib.sh) by default. Consider 64 making use of the defer primitive to schedule automatic cleanups. This 65 makes it harder to forget to remove a temporary netdevice, kill a running 66 process or perform other cleanup when the test script is interrupted. 67 68o When adding a helper that dirties the environment, but schedules all 69 necessary cleanups through defer, consider prefixing it adf_ for 70 consistency with lib.sh and ../lib.sh helpers. This serves as an 71 immediately visible bit of documentation about the helper API. 72 73o Definitely do the above for any new code in lib.sh, if practical. 74 75Customization 76============= 77 78The forwarding selftests framework uses a number of variables that 79influence its behavior and tools it invokes, and how it invokes them, in 80various ways. A number of these variables can be overridden. The way these 81overridable variables are specified is typically one of the following two 82syntaxes: 83 84 : "${VARIABLE:=default_value}" 85 VARIABLE=${VARIABLE:=default_value} 86 87Any of these variables can be overridden. Notably net/forwarding/lib.sh and 88net/lib.sh contain a number of overridable variables. 89 90One way of overriding these variables is through the environment: 91 92 PAUSE_ON_FAIL=yes ./some_test.sh 93 94The variable NETIFS is special. Since it is an array variable, there is no 95way to pass it through the environment. Its value can instead be given as 96consecutive arguments to the selftest: 97 98 ./some_test.sh swp{1..8} 99 100A way to customize variables in a persistent fashion is to create a file 101named forwarding.config in this directory. lib.sh sources the file if 102present, so it can contain any shell code. Typically it will contain 103assignments of variables whose value should be overridden. 104 105forwarding.config.sample is available in the directory as an example of 106how forwarding.config might look. 107