infix/src/net

net - an iproute2 wrapper

The net tool is a wrapper around the iproute2 and ethtool programs to set up networking on a Linux system. It also handles transitions from a previously configured state to the next while attempting to keep the amount of changes needed to a minimum.

Concept Overview

net applies a configuration from /run/net/next, where next is a file that holds the number of the next net generation. It is up to the user, i.e., sysrepo, to create the below tree structure with commands to run.

The setup we start with and later move eth4 from lag0 to br0.

           vlan1
     ______/____
    [____br0____]
    /  /   \    \
eth1 eth2 eth3  lag0
                /  \
             eth4  eth5

Consider the case when next contains 0, net reads all interfaces, in dependency order, from /run/net/0/ running all init.cmd scripts. When done, it writes 0 to the file /run/net/gen and then removes the next file to confirm the generation has been activated.

Note: it is currently up to the user to remove any old generation.

 /run/net/0/
   |-- br0/
   |    |-- deps/
   |    |    |-- eth1 -> ../../eth1
   |    |    |-- eth2 -> ../../eth2
   |    |    |-- eth3 -> ../../eth3
   |    |    `-- lag0 -> ../../lag0
   |    |-- admin-state
   |    `-- init.ip
   |-- eth0/
   |    |-- deps/
   |    |-- admin-state
   |    `-- init.ip
   |-- ethX/
   |    |-- ...
   :    :
   |-- lag0/
   |    |-- deps/
   |    |    |-- eth4 -> ../../eth4
   |    |    `-- eth5 -> ../../eth5
   |    |-- admin-state
   |    `-- init.ip
   `-- vlan1/
        |-- deps/
        |    `-- br0 -> ../../br0
        |-- admin-state
        `-- init.ip

The deps/ sub-directory for each of the interfaces contains symlinks to any interfaces this interface may depend on. I.e., those interfaces are evaluated first.

Essentially, all leaves must be set up before their parents. Moving a leaf from one parent to another, e.g., from lag0 to br0, is tricky, it involves traversing the previous dependency order when removing leaves, and traversing the next dependency order when adding, see next section for an example.

Example

net is built to complement sysrepo. The idea is to listen to any added, deleted, modified states in sysrepo changes to a candidate configuration and generate the next generation. However, as mentioned previously, when moving leaves between parents we must do so in the dependency order of the current generation.

So, the user (sysrepo) needs to add exit.cmd scripts in the current tree for every leaf that leaves a parent, and init.cmd scripts for leaves that are new or added to parents in the next generation.

In our example, interface eth4 is moved from lag0 to br0, so we need to run eth4/exit.ip in the current generation first to remove eth4 from lag0 before its init.ip script in the next generation sets eth4 as a bridge member instead.

We traverse the current generation and execute all exit.cmd scripts:

/run/net/<GEN>/
   |-- br0/
   |    |-- deps/
   |    |    |-- eth1 -> ../../eth1
   |    |    |-- eth2 -> ../../eth2
   |    |    |-- eth3 -> ../../eth3
   |    |    `-- lag0 -> ../../lag0
   |    |-- admin-state
   |    `-- init.ip
   |-- eth0/
   |    |-- deps/
   |    |-- admin-state
   |    `-- init.ip
   |-- eth4/
   |    |-- deps/
   |    |-- admin-state
   |    |-- exit.ip
   |    `-- init.ip
   |-- lag0/
   |    |-- deps/
   |    |    |-- eth4 -> ../../eth4
   |    |    `-- eth5 -> ../../eth5
   |    |-- admin-state
   |    `-- init.ip
   `-- vlan1/
        |-- deps/
        |    `-- br0 -> ../../br0
        |-- admin-state
        `-- init.ip

Now we can run all the init.cmd scripts in the next generation:

/run/net/<GEN+1>/
   |-- br0/
   |    |-- deps/
   |    |    |-- eth1 -> ../../eth1
   |    |    |-- eth2 -> ../../eth2
   |    |    |-- eth3 -> ../../eth3
   |    |    |-- eth4 -> ../../eth4
   |    |    `-- lag0 -> ../../lag0
   |    |-- admin-state
   |    `-- init.ip
   |-- eth0/
   |    |-- deps/
   |    |-- admin-state
   |    `-- init.ip
   |-- eth4/
   |    |-- deps/
   |    |-- admin-state
   |    `-- init.ip
   |-- lag0/
   |    |-- deps/
   |    |    `-- eth5 -> ../../eth5
   |    |-- admin-state
   |    `-- init.ip
   `-- vlan1/
        |-- deps/
        |    `-- br0 -> ../../br0
        |-- admin-state
        `-- init.ip

When there are no changes compared to the previous generation, the base structure with deps need to remain intact, but there's no need for any init.cmd scripts. However, for the purpose of supporting the commands net down and net up, the user must have an admin-state file per interface which must contain one of:

• disabled
• up
• down

This describes the state which the user's last init.ip or exit.ip command, or the net [up | down] action, left the interface in. When the disabled keyword is used it means the net tool is not allowed to apply any up or down action on the interface.