Saturday, April 02, 2016

Minimal illumos networking

Playing around with Minimal Viable Illumos, it becomes clear how complex a system illumos is. Normally, if you're running a full system, everything is taken care of for you. In particular, SMF starts all the right services for you. Looking through the method scripts, there's a lot of magic happening under the hood.

If you start with a bare install, booted to a shell, with no startup scripts having run, you can then bring up networking automatically.

The simplest approach would be to use ifconfig to set up a network interface. For example

ifconfig e1000g0 plumb up

This won't work. It will plumb the interface, but not assign the address. To get the address assigned, you need to have ipmgmtd running.

env SMF_FMRI=svc/net/ip:d /lib/inet/ipmgmtd

Note that SMF_FMRI is set. This is because ipmgmtd expects to be run under SMF, and checks for SMF_FMRI being set as the determinant. It doesn't matter what the value is, it just needs to exist.

OK, so if you know your network device and your address, that's pretty much it.

If you use dladm to look for interfaces, then you'll see nothing. In order for dladm show-phys to enumerate the available interfaces, you need to start up dlmgmtd and give it a poke

env SMF_FMRI=svc/net/dl:d /sbin/dlmgmtd
dladm init-phys

Note that SMF_FMRI is set here, just like for ipmgmtd.

At this point, dladm show-phys will give you back the list of interfaces as normal.

You don't actually need to run dladm init-phys. If you know you have a given interface, plumbing it will poke enough of the machinery to make it show up in the list.

If you don't know your address, then you might think of using dhcp to assign it. This turns out to require a bit more work.

The first thing you need to do is bring up the loopback.

ifconfig lo0 plumb up
ifconfig lo0 inet6 plumb ::1 up

This is required because dhcpagent wants to bind to localhost:4999, so you need the loopback set up for it to be able to do that. (You don't necessarily need the IPv6 version, that's for completeness.)


ifconfig e1000g0 plumb
ifconfig e1000g0 auto-dhcp primary

Ought to work. Sometimes it does, sometimes it doesn't.

I sometimes found that I needed to

dladm init-secobj

in order to quieten errors that occasionally appear, and sometimes need to run

ifconfig -adD4 auto-revarp netmask + broadcast + up

although I can't even imagine what that would do to help, I presume that it kicks enough of the machinery to make sure everything is properly initialized.

Within the context of mvi, setting a static IP address means you need to craete a new image for each IP address, which isn't actually too bad (creating mvi images is really quick), but isn't sustainable in the large. DHCP would give it an address, but then you need to track what address a given instance has been allocated. Is there a way of doing static IP by poking the values from outside?

A tantalizing hint is present at the end of /lib/svc/method/net-physical, where it talks about boot properties being passed in. The implementation there appears to be aimed at Xen, I'll have to investigate if it's possible to script variables into the boot menu.