VLAN MTU problem in 4.9 ?

[Stephane Raimbault]

Thanks for all your help regarding this problem... I was able to "fix" my 
problem (for lack of better word) by doing the following

deleting the inet address on xl1 and manually re-adding it.  I'm not sure 
why this fixed my problems, but I can ping my servers behind the router with 
pings sizes greater then 1468 bytes "ping -s 1469 <IP Address">.

It seems that at startup, something messes up the vlan setup. here is what I 
have in my /etc/rc.conf


ifconfig_xl0="inet 10.0.0.3 netmask 255.255.255.192"
ifconfig_xl1="inet 207.176.232.142 netmask 255.255.255.224"
ifconfig_vlan0="inet 10.0.1.3 netmask 255.255.255.224 vlan 3 vlandev xl1"
ifconfig_vlan0_alias0="inet 10.0.1.1 netmask 255.255.255.255"
ifconfig_vlan1="inet 10.0.11.3 netmask 255.255.255.224 vlan 4 vlandev xl1"
ifconfig_vlan1_alias0="inet 10.0.11.1 netmask 255.255.255.255"
defaultrouter="207.176.232.158"

For some reason, doing an "ifconfig xl1 delete 207.176.232.142" followed by 
"ifconfig xl1 inet 207.176.232.142 netmask 255.255.255.224" allows me to 
ping the servers with the ping sizes I couldn't before... perhaps the inet 
interface on the device needs to be set after the vlan interfaces?

Any thoughts?

Thanks,
Stephane.

>From: . at babolo.ru
>To: Stephane Raimbault <segr at hotmail.com>
>CC: net at freebsd.org
>Subject: Re: VLAN MTU problem in 4.9 ?
>Date: Fri, 2 Jan 2004 21:29:43 +0300 (MSK)
>
> > Setting the MTU to 1496 on the router vlan interfaces didn't seem to 
>help
> > me... however put the MTU to 1496 on the servers on the VLAN itself 
>seems to
> > resolve the problem.  so in the current configuration the router vlan
> > interfaces are set to 1500 and the servers on those interfaces are set 
>to
> > 1496.  Seems to work for now.
> >
> > Now, this doesn't seem all that normal.  Where can I go from here to
> > troubleshoot this more and provide more information that might be able 
>to
> > resolve this problem... if it's a problem that is...
>You can't be free from tune all your net for vlan mtu:
>  - all switches involved must be at least verifyed not to drop long frames
>    or right route vlans if it can work with tag based vlans
>  - all interfaces in selected vlan must support the same common mtu
>
>I know now, that xl interface can't pass 1504 frames
>and most 1G interfaces can
>  don't know about another 100M interfaces
>

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