Re: [RFC] ifconfig: match by link-level address
From: Peter Pentchev (roam_at_ringlet.net)
Date: 05/21/04
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Date: Fri, 21 May 2004 10:04:23 +0300 To: Brooks Davis <brooks@one-eyed-alien.net>
On Thu, May 20, 2004 at 10:18:38AM -0700, Brooks Davis wrote:
> On Thu, May 20, 2004 at 07:29:19PM +0300, Peter Pentchev wrote:
> > Hi,
> >
> > I found out recently that the Linux (or at least recent RedHat) startup
> > scripts could be configured to not bring up an Ethernet interface unless
> > it has a specified MAC address. This, combined with the wonderful
> > interface renaming functionality recently committed to -CURRENT, led me
> > to the idea of interface renaming on boot-up, by hardware addresses -
> > something like 'I don't care how you detected this network card, or how
> > many others like it are there, but the card with MAC address
> > 00:03:0d:08:dc:a7 will be known as sis0int from now on'.
> >
> > The main missing piece was the ability to find an interface by MAC
> > address; hence the attached patch, also available at
> > http://www.ringlet.net/~roam/bsd-patches/src5/sbin-ifconfig-hwmatch.patch
> > http://people.FreeBSD.org/~roam/bsd-patches/src5/sbin-ifconfig-hwmatch.patch
> >
> > It teaches ifconfig(8) to treat interface "names" beginning with 'hw-'
> > as link-level addresses; ifconfig tries to find an interface with this
> > address and behaves as if its name was specified on the command line:
> >
> > [roam@straylight ~/fbsd/r/src/sbin/ifconfig]> ./ifconfig hw-00:03:0d:08:dc:a7
> > sis0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> > options=8<VLAN_MTU>
> > inet 10.0.8.129 netmask 0xffff0000 broadcast 10.0.255.255
> > inet 192.168.1.13 netmask 0xffffff00 broadcast 192.168.1.255
> > ether 00:03:0d:08:dc:a7
> > media: Ethernet autoselect (100baseTX <full-duplex>)
> > status: active
> > [roam@straylight ~/fbsd/r/src/sbin/ifconfig]>
> >
> > This could be the first step towards teaching rc.conf about something like
> > network_interfaces_rename="hw-00:03:0d:08:dc:a7 sis0int"
> >
> > I had initially written my own function for parsing the user-supplied
> > address into a sequence of bytes instead of using ether_aton(); it would
> > have the advantage of being able to specify 'hw-' to match lo0's empty
> > link-level "address". However, the odds of somebody actually wishing to
> > rename lo0 don't seem to be so high :)
>
> I don't really like the idea of adding magic values to the interface
> namespace that only work with ifconfig. If you want ifconfig to match
> the lladdr, I'd suggest adding a flag that means match interface by
> address instead of by name. That would be a fairly simple change to
> your patch and seems like a potentialy useful feature.
Agreed, I don't like the magic hw- too much either, but.. see below for
more comments on this and interface renaming on startup.
> FWIW, I've talked to Warner about automaticly renaming interfaces based
> on things like their MAC address or their PCI slot and we think devd
> will eventually be the place to do this. We're probably going to have
> to rethink interface configuration for this to work though.
Well, it turned out that adding basic interface renaming support to our
startup scripts wasn't all that hard - the attached patch, also at
http://www.ringlet.net/~roam/bsd-patches/src5/etc-iface-rename.patch
http://people.FreeBSD.org/~roam/bsd-patches/src5/etc-iface-rename.patch
seems to work for both 'sis0 ethlocal xl0 ethext' and
'hw-00:03:0d:08:dc:a7 ethlocal', since it just passes the interface name
to ifconfig(8).
If the link-level address matching should be done with a separate
ifconfig(8) option, the interface renaming may need to be split into two
stages controlled by two configuration variables - one specifying the
'source' interface by name, the other one by address, with the latter
code using the new ifconfig option.
Of course, this still leaves a problem with specifying the address for
an interface that has not yet been 'found' - after all, we can't
ifmaybeload() a driver on just the link-level address of the card. This
is a case when devd might be a better solution indeed. However, I don't
think that people who use interface renaming will depend on the system
automatically discovering the *types* of network cards: if you know the
MAC address of the card, you'll probably know just what brand and model
it is, too :)
G'luck,
Peter
-- Peter Pentchev roam@ringlet.net roam@sbnd.net roam@FreeBSD.org PGP key: http://people.FreeBSD.org/~roam/roam.key.asc Key fingerprint FDBA FD79 C26F 3C51 C95E DF9E ED18 B68D 1619 4553 This sentence contradicts itself - or rather - well, no, actually it doesn't!
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