iproute2 Cheat Sheet by TME520

Metasy­ntactic variables are written in shell-­style syntax, ${some­thing}. Optional command parts are in square brackets. Note that there is no way to rearrange addresses and replace the primary address. Make sure you set the primary address first.

As per the section below, if you set up a static route, and it becomes useless because the interface goes down, it will be removed and never get back on its own. You may not have noticed this behaviour because in many cases additional software (e.g. Networ­kMa­nager or rp-pppoe) takes care of restoring routes associated with interf­aces.

Note that interface name you set with "name ${name­}" parameter of "ip link add" and "ip link set" commands may be arbitrary, and even contain unicode charac­ters. It's better however to stick with ASCII because other programs may not handle unicode correctly. Also it's better to use a consistent convention for link names, and use link aliases to provide human descri­ptions.

Link groups are similar to port ranges found in managed switches. You can add network interfaces to a numbered group and perform operations on all the interfaces from that group at once.

Links not assigned to any group belong to group 0 aka "­def­aul­t".

Tun and tap devices allow userspace programs to emulate a network device. When the userspace program opens them they get a file descri­ptor. Packets routed by the kernel networking stack to the device are read from the file descri­ptor, data the userspace program writes to the file descriptor are injected as local outgoing packets into the networking stack.

For ladies and gentlemen who prefer UK spelling, this command family supports "­nei­ghb­our­" spelling too.

Linux currently supports IPIP (IPv4 in IPv4), SIT (IPv6 in IPv4), IP6IP6 (IPv6 in IPv6), IPIP6 (IPv4 in IPv6), GRE (virtually anything in anything), and, in very recent versions, VTI (IPv4 in IPsec).

Note that tunnels are created in DOWN state, you need to bring them up.

In this section ${local endpoint address} and ${remote endpoint address} refer to addresses assigned to physical interfaces of endpoint. ${address} refers to the address assigned to tunnel interface.

Compared to other tunneling protocol implem­ent­ations in Linux, L2TPv3 termin­ology is somewhat reversed. You create a tunnel, and then bind sessions to it. You can bind multiple sessions with different identi­fiers to the same tunnel. Virtual network interfaces (by default named l2tpethX) are associated with sessions.

Policy­-based routing (PBR) in Linux is designed the following way: first you create custom routing tables, then you create rules to tell the kernel it should use those tables instead of the default table for specific traffic.

Some tables are predef­ined: local (table 255), main (table 254), default (table 253).

Network namespaces are isolated network stack instances within a single machine. They can be used for security domain separa­tion, managing traffic flows between virtual machines and so on.

Every namespace is a complete copy of the networking stack with its own interf­aces, addresses, routes etc. You can run processes inside a namespace and bridge namespaces to physical interf­aces.

Multicast is mostly handled by applic­ations and routing daemons, so there is not much you can and should do manually here. Multic­ast­-re­lated ip commands are mostly useful for debug.

You can monitor certain network events with iproute2, such as changes in network config­ura­tion, routing tables, and ARP/NDP tables.