Tuesday, 9 May 2017

If you're still using ifconfig, you're living in the past

The world evolves

I regularly see "recommendations" to use ifconfig to get interface information in mailing list posts or bug reports and other places. I might even be guilty of it myself. Still, the world of networking has evolved quite a lot since ifconfig was the de-facto standard to bring up a device, check its IP or set an IP.

Following some improvements in the kernel and the gradual move to driving network things via netlink; ifconfig has been largely replaced by the ip command.

Running just ip yields the following:

Usage: ip [ OPTIONS ] OBJECT { COMMAND | help }
       ip [ -force ] -batch filename
where  OBJECT := { link | address | addrlabel | route | rule | neigh | ntable |
                   tunnel | tuntap | maddress | mroute | mrule | monitor | xfrm |
                   netns | l2tp | fou | macsec | tcp_metrics | token | netconf | ila }
       OPTIONS := { -V[ersion] | -s[tatistics] | -d[etails] | -r[esolve] |
                    -h[uman-readable] | -iec |
                    -f[amily] { inet | inet6 | ipx | dnet | mpls | bridge | link } |
                    -4 | -6 | -I | -D | -B | -0 |
                    -l[oops] { maximum-addr-flush-attempts } | -br[ief] |
                    -o[neline] | -t[imestamp] | -ts[hort] | -b[atch] [filename] |
                    -rc[vbuf] [size] | -n[etns] name | -a[ll] | -c[olor]}

I understand this may look complicated to some people, but the jist of it is to understand that with ip, you interact with objects, and apply some kind of function to it. For example:

ip address show

This is the main command that would be used in place of ifconfig. It will just display the IP addresses assigned to all interfaces. To be precise, it will show you the layer 3 details the interface: the IPv4 and IPv6 addresses, whether it is up, what are the different properties related to the addresses...

Another command will give you details about the layer 2 properties of the interface: its MAC address (ethernet address), etc; even if it is shown by ip address:

ip link show

Furthermore, you can set devices up or down (similar to ifconfig eth0 up or ifconfig eth0 down) simply by using:

ip link set DEVICE up or ip link set DEVICE down

As shown above, there are lots of other objects that can be interacted with using the ip command. I'll cover another: ip route, in another post.

Why is this important?

As time passes, more and more features are becoming easier to use with the ip command instead of with ifconfig. We've already stopped installing ifconfig on desktops (it still gets installed on servers for now), and people have been discussing dropping net-tools (the package that ships ifconfig and a few other old commands that are replaced) for a while now. It may be time to revisit not installing net-tools by default anywhere.

I want to know about your world

Are you still using one of the following tools?

/bin/netstat    (replaced by ss, for which I'll dedicate another blog post entirely)
/sbin/ipmaddr   (replaced by ip maddress)
/sbin/mii-tool    (ethtool should appropriately replace it)

If so and there is just no alternative to using them that comes from iproute2 (well, the ip or ss commands) that you can use to do the same, I want to know about how you are using them. We're always watching for things that might be broken by changes; we want to avoid breaking things when possible.


Unknown said...

I added alias ip='ip -c' to my .bashrc.
It makes the ip output so much more readable

Jamie Knight said...

I still use ifconfig/netstat/route quite extensively. Partly because that's what I've grown up using, but also because (at work) I manage non-Linux-but-still-*nix systems - where those commands are pretty much always present, as opposed to the newer but (exclusively Linux?) iproute2 ones.

However the outputs are different enough on each platform that cross-platform scripting isn't really feasible. (Or at least reliable.) We only ever use the "classic" commands when we're on a terminal. :)

Mathieu Trudel-Lapierre said...

Jamie; I agree, I also have extensive muscle-memory that forces me to think before running this or that command. That's why I posted this. It's unfortunate but unavoidable that there are still systems that rely exclusively on ioctls/ifconfig and all of that makes cross-platform scripting hard. That said; there's only so much cross-platform you can do anyway, features quickly don't match up.

Gord Campbell said...

"ip address show" is so much easier than ifconfig -- not.