Q: How to change to MTU 9000 Jumbo Frames ?

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fortechitsolutions

Renowned Member
Jun 4, 2008
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Hi all, sorry if this is 'blazing obvious' but I'm still getting the feel of this.

I have 2 Proxmox VE machines connected via gig-ether with intel e1000 NICs. All gear (2 servers, the switch) support jumbo frame MTU=9000

I can issue as root on console of the ProxmoxVE servers a command thus,

ifconfig eth0 mtu 9000

and this works fine. The single (Default config) bridged interface is bumped up to MTU 9000 as well.

I then try to make this a persistent configuration change, by editing the file,

/etc/network/interfaces

and adding "mtu 9000" to the stanza for the bridge interface, so things appear thus:

pvm1:/etc/network# more interfaces
auto lo
iface lo inet loopback

auto vmbr0
iface vmbr0 inet static
address 10.10.2.11
netmask 255.255.255.0
gateway 10.10.2.1
mtu 9000
bridge_ports eth0
bridge_stp off
bridge_fd 0
pvm1:/etc/network#


However when I restart network services, an error is returned and the MTU isn't set. I assume this is because I can't set MTU on the vmbr0 device (it is a bridge against eth0) - rather, the setting needs to be made on eth0 itself.

Alas, I can't really see here how eth0 is being configured at all (?!) - it isn't cited in the 'interfaces' file....

Is this a matter, that I need to add a section to the interfaces file for eth0 - where I specify only the MTU parameter.. and then let this be inherited by the vmbr device... (?)

Any pointers / suggestions are most welcome.

Thanks,


---Tim
 
mtu 9000

fortechitsolutions said:
and adding "mtu 9000" to the stanza for the bridge interface, so things appear thus:

pvm1:/etc/network# more interfaces
auto lo
iface lo inet loopback

auto vmbr0
iface vmbr0 inet static
address 10.10.2.11
netmask 255.255.255.0
gateway 10.10.2.1
mtu 9000
bridge_ports eth0
bridge_stp off
bridge_fd 0
pvm1:/etc/network#


However when I restart network services, an error is returned and the MTU isn't set. I assume this is because I can't set MTU on the vmbr0 device (it is a bridge against eth0) - rather, the setting needs to be made on eth0 itself.


---Tim
Click to expand...

Do so:

pvm1:/etc/network

:interfaces

auto lo
iface lo inet loopback

auto vmbr0
iface vmbr0 inet static
address 10.10.2.11
netmask 255.255.255.0
gateway 10.10.2.1
#mtu 9000
bridge_ports eth0
bridge_stp off
bridge_fd 0
up "ifconfig eth0 mtu 9000||true"

pvm1:/etc/network#

Ciao, Diaolin
 
Hi,

Many thanks for the reply. Alas, I'm not certain why but this doesn't appear to work. It returns an error, 'command not found', when I make this change and restart networking.

What I see is,

--paste--
pvm1:/etc/network# vi interfaces

pvm1:/etc/network# /etc/init.d/networking restart
Reconfiguring network interfaces...device vmbr0 already exists; can't create bridge with the same name

Waiting for vmbr0 to get ready (MAXWAIT is 2 seconds).

/bin/sh: ifconfig eth0 mtu 9000||true: command not found

Failed to bring up vmbr0.
done.


What I've got in interfaces file is now, as per your suggestion:

pvm1:/etc/network# more interfaces
auto lo
iface lo inet loopback

auto vmbr0
iface vmbr0 inet static
address 10.10.2.11
netmask 255.255.255.0
gateway 10.10.2.1
bridge_ports eth0
bridge_stp off
bridge_fd 0
up "ifconfig eth0 mtu 9000||true"


--endpaste--


If you have any further comments or thoughts; certainly they are appreciated.


Thanks for your help with this ..

--Tim
 
Hi,

Bit of an update. I did a bit more digging with google, and after a few trial and error kicks at this, I think it now works as desired. Thanks for your suggestion - it is what got me there :-)

--Tim


---paste---
CURRENT WORKING CONFIG:

pvm1:/etc/network# more interfaces
auto lo
iface lo inet loopback

auto vmbr0
iface vmbr0 inet static
address 10.10.2.11
netmask 255.255.255.0
gateway 10.10.2.1
bridge_ports eth0
bridge_stp off
bridge_fd 0
pre-up ifconfig eth0 mtu 9000
#
# Note these next 2 lines are failed attempts that did not work..
# pre-up "/sbin/ifconfig eth0 mtu 9000"
#up "ifconfig eth0 mtu 9000||true"

Now we see:
pvm1:/etc/network# /etc/init.d/networking restart
Reconfiguring network interfaces...
Waiting for vmbr0 to get ready (MAXWAIT is 2 seconds).
done.
pvm1:/etc/network#

and the inteface has MTU 9000 shown:


pvm1:/etc/network# ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:15:17:8E:45:3D
inet6 addr: fe80::215:17ff:fe8e:453d/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:9000 Metric:1
RX packets:335414 errors:0 dropped:12 overruns:0 frame:0
TX packets:376859 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:108382139 (103.3 MiB) TX bytes:242330024 (231.1 MiB)
Memory:e3b00000-e3b20000
...etc...
 
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