[Solved, with caveat] MTU and dhcp

Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

say I have the following lines in /etc/conf.d/net:

Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

bump
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lonex · Posted: Sat Oct 06, 2007 5:02 pm Post subject:

You just have to add the following line, so that dhcpcd doesn't set the MTU to what the dhcp server says:

Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

I cannot find that '-M' dhcpcd flag documented anywhere at all. Are you sure you're not thinking of some other DHCP clilent?
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lonex · Posted: Sun Oct 07, 2007 7:18 am Post subject:

I've read man dhcpcd ... and there it is?

Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

Ah, so the unstable dhcpcd is required. Small price to pay I suppose. Great! Thanks.
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UberLord · Posted: Wed Oct 10, 2007 8:57 am Post subject:

3.1.5 is stable on most arches, and has been for a while now.
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When baselayout tells you to update config files or things break WE REALLY DO MEAN IT

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Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

I'm kind of running my own tree right now, maintaining a bunch of near-identical servers, so naturally the official tree and mine don't quite match. It can't have been THAT long ago, my tree's not THAT old either.

I'm quite suprised they made it stable already though, since I noticed a few issues when I went and tested it's behavior on timeout! I don't see anything about these issues in the changelog either, Gentoo's or dhcpcd's, so I presume they still stand.

zeroconf is enabled by default! If it times out, it will autoconfigure to some bizzare address in 169.x.y.z(anyone else remember this headache from the Windows 98 days?) instead of using your failovers in /etc/conf.d/net . Give dhcpcd the "-L" flag to stop it doing this.

If it still has a lease in cache, when it times out, it will use that lease instead of using your failovers in /etc/conf.d/net . There's no "please don't use cache" commandline flag, and the "please delete cache" flag doesn't work unless dhcpcd is already running, so you have to just go and delete the cache yourself before dhcpcd gets run. Putting it in the preup() function in /etc/conf.d/net was fairly convenient, like so:

Code:

# Disable zeroconf(-L) and don't mung wan's MTU(-M)
dhcpcd_wan="-M -L"

# Remove cache for interface! arrrggh!!!!
preup() {
if [[ "${IFACE}" == "wan" ]]
then
# Destroy cache so it can't interfere with fallbacks!
if [[ -f "/var/run/dhcpcd-${IFACE}.pid" ]]
then
einfo "Clearing dhcpcd cache for ${IFACE} ..."
dhcpcd -k ${IFACE} 2> /dev/null > /dev/null
eend
fi

if [[ -f "/var/lib/dhcpcd/dhcpcd-${IFACE}.info" ]]
then
einfo "Burning dhcpcd cache for ${IFACE} ..."
rm -f /var/lib/dhcpcd/dhcpcd-${IFACE}.info
eend
fi
fi
}

Rather obnoxious when you're trying to maintain servers over satellite links...
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UberLord · Posted: Thu Oct 11, 2007 8:50 pm Post subject:

serial_penguin · Posted: Fri Oct 12, 2007 10:48 pm Post subject:

Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

UberLord · Posted: Tue Oct 16, 2007 10:28 am Post subject:

Did you know that I maintain baselayout as well?

Also, moaning on the forums doesn't make me want to change anything. Most devs don't read the forums, so you need to file a bug to get their attention.
Maybe you want to file a bug against dhcpcd to add warnings about zeroconf and the -L option.
Maybe you want to file a bug against baselayout to document this in net.example.
_________________
When baselayout tells you to update config files or things break WE REALLY DO MEAN IT

Please add SOLVED to the thread title if your issue has been
Strip comments from configs please

Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

UberLord · Posted: Tue Oct 16, 2007 4:45 pm Post subject:

One other dev aside from me currently contributes to baselayout, but I do around 99% of the work.
http://sources.gentoo.org/viewcvs.py/baselayout/trunk/

Sorry, it was your tone that I was referring to. Forums are a perfectly legit place to note problems and their solutions.

No, it's a behaviour change in dhcpcd. baselayout thinks dhcpcd succeeded when dhcp fails and it gets a local link address. But then, with a zeroconf implementation it will never fail, so it will always "work" from baselayouts view.
Now, dhcpcd is NOT a Gentoo project as such I didn't feel a massive need to inform the world about this "behaviour" change. Even if I did then it would be to the dhcpcd mailing list subscribers.

Now hands up how many people run ~ARCH or unstable dhcpcd? I ask as it's been there for two months, and you're the first to complain about this specific feature.
Maybe more people should help test.
_________________
When baselayout tells you to update config files or things break WE REALLY DO MEAN IT

Please add SOLVED to the thread title if your issue has been
Strip comments from configs please

UberLord · Posted: Tue Oct 16, 2007 4:50 pm Post subject:

I just saw your bug. OK, so jakub our sometime over zealous bug-wrangler marked it as a dupe. Maybe a better bug would be as follows

Corona688 · Veteran Joined: 10 Jan 2004 Posts: 1204

UberLord · Posted: Wed Oct 17, 2007 9:02 am Post subject:

I failed to maintain that I am upstream for dhcpcd, baselayout and maintain both ebuilds as well. I also lead the Gentoo/FreeBSD effort and currently preside on the Gentoo Council.
I also maintain the other DHCP v4 ebuilds.

Now, we'll move this conversation to the bug

_________________
When baselayout tells you to update config files or things break WE REALLY DO MEAN IT

Please add SOLVED to the thread title if your issue has been
Strip comments from configs please