Date: Mon, 13 Jul 2015 09:33:42 +0100 From: Karl Pielorz <kpielorz_lst@tdx.co.uk> To: John-Mark Gurney <jmg@funkthat.com> Cc: freebsd-net@freebsd.org Subject: Re: lagg of em0/em1 + VLAN = lower MTU? Message-ID: <EF441569FCACD78034320411@[10.12.30.106]> In-Reply-To: <20150710180627.GA8523@funkthat.com> References: <7CFE75F7566F5789DAD9FBB2@[10.12.30.106]> <20150710180627.GA8523@funkthat.com>
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--On 10 July 2015 11:06 -0700 John-Mark Gurney <jmg@funkthat.com> wrote:
> Try bumping the MTU on the root em's by 4 (1504) before creating the
> lagg...
I had thought of that - but didn't want to try it (on the basis that out of
all the other example config's I've seen - no one else has to, and it will
break the lagg MTU).
Anyway I tried it, by:
- Bump the MTU on the em interfaces before creating the lagg to 1504
- The lagg created, inherits this 1504 MTU
That breaks the untagged IP on lagg0 - i.e. I end up with:
"
lagg0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1504
options=4019b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4,VLAN_HWTSO>
ether 68:05:ca:08:1d:3b
inet x.x.x.x netmask 0xffffff00 broadcast y.y.y.y
"
That MTU of 1504 is going to break lagg0 for untagged traffic :(
- However, the VLAN's setup on the lagg still default to 1496 MTU (despite
the underlying interface lagg0 being MTU 1504)
If I 'manually' bump the MTU on the individual lagg0.x VLAN interfaces -
they will go to 1500, but traffic is still 'broken'.
I can't 'reduce' the bad MTU on lagg0 either - i.e. 'ifconfig lagg0 mtu
1500' (to try to put it back to 1500) fails with an ioctl error.
So sadly, I'm still stuck :(
Something is lopping 4 bytes off the MTU when it shouldn't need to. None of
the example configs I could find were from 10.1-R (or with exactly the same
cards) - but obviously this is just bread & butter lagg/VLAN stuff, so it
should work?
-Karl
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