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Steven Anderson

2005-Dec-19 18:25 UTC

[Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces

Greetings! Happy Holiday Season!
 
 I am able to put the MTU setting for physical interfaces like eth0 in
/etc/sysconfig/network-scripts/ifcfg-eth0
 the paramterer is called MTU 
 I am also to do it on the fly with ifconfig eth0 mtu 1492
 
 However the on the fly fails with the peth0 interface ( which I am not sure
what it does anyways? Anyone Know?)
 
 MY BIGGEST PROBLEM  is for the xen specific interfaces such as xenbr0 vif1.0 in
both dom0 and domU I would like to set them all to 1492 which I I might later
change to 1400 ...Anyone know how to specify MTU=1492 and where to do it for
those interfaces???????????????????????????
 
 NOTE: from what i understand 802.1q doesnt work properly unless you make a MTU
less than 1000 on some interfaces ( anyone with details on this ...I welcome
your comments since after getting the basics I might implement this later on my
test system)
 
 
 Thanks in advance!
 
 Happy Holidays!
 
 
 
  

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Steven Anderson

2005-Dec-19 23:42 UTC

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[Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces

Been investigating perminetly changing the MTU size in the setup scripts.
 
 This is what I have tried but failed to get it to make changes
 
 added wherever #added appears (note did not use "#added" in the
actual scripts)
 
 
 The vif-route script in /etc/xen/scripts contains
 __________________________________________________
 dir=$(dirname "$0")
 . "$dir/vif-common.sh"
 
 main_ip=$(dom0_ip)
 
 case "$command" in
     online)
         ifconfig ${vif} ${main_ip} netmask 255.255.255.255 up
   #added          if [[ "${vif}" == "peth0" ]] ; then
    #added         else
     #added         ifconfig ${vif} mtu 1492
      #added        fi
         echo 1 >/proc/sys/net/ipv4/conf/${vif}/proxy_arp
         ipcmd=''a''
         ;;
     offline)
         ifdown ${vif}
         ipcmd=''d''
         ;;
 ___________________________________________________
 
 I tried adding the lines above but it had no effect on the interface. I guess i
dont understand when this scipt is run or some other fundamental
components....I''m no programmer. Can anyone tell me why it only changes
the eth0 interface on dom0?????
 
 
 
 
 
 

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Erik

2005-Dec-20 07:58 UTC

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Re: [Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces

Steven,

Why would you want to change the MTU, som applications won''t like a non
standard (<1500) MTU, we use a MTU of 1504 on our 802.1q interface (an e1000)
in Dom0 to bridge vlan interfaces to domU and preserve a 1500 byte mtu, mtu 1504
should work without setting it as the kernel support 802.1q framing
(1500 byte + 4 byte vlan tag).

Erik


Steven Anderson wrote:> Been investigating perminetly changing the MTU size in the setup scripts.
> 
> This is what I have tried but failed to get it to make changes
> 
> added wherever #added appears (note did not use "#added" in the
actual
> scripts)
> 
> 
> The vif-route script in /etc/xen/scripts contains
> __________________________________________________
> dir=$(dirname "$0")
> . "$dir/vif-common.sh"
> 
> main_ip=$(dom0_ip)
> 
> case "$command" in
>     online)
>         ifconfig ${vif} ${main_ip} netmask 255.255.255.255 up
>   #added          if [[ "${vif}" == "peth0" ]] ; then
>    #added         else
>     #added         ifconfig ${vif} mtu 1492
>      #added        fi
>         echo 1 >/proc/sys/net/ipv4/conf/${vif}/proxy_arp
>         ipcmd=''a''
>         ;;
>     offline)
>         ifdown ${vif}
>         ipcmd=''d''
>         ;;
> ___________________________________________________
> 
> I tried adding the lines above but it had no effect on the interface. I
> guess i dont understand when this scipt is run or some other fundamental
> components....I''m no programmer. Can anyone tell me why it only
changes
> the eth0 interface on dom0?????
> 
> 
> 
> 
> 
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users

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Steven Anderson

2005-Dec-20 12:17 UTC

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[Xen-users] Re: MTU-1492 Permenent Setting for Xen Specific Interfaces

Eric Wrote:
 
"Steven,

Why would you want to change the MTU, som applications won''t like a non
standard (<1500) MTU, we use a MTU of 1504 on our 802.1q interface (an 
e1000)
in Dom0 to bridge vlan interfaces to domU and preserve a 1500 byte mtu, 
mtu 1504 should work without setting it as the kernel support 802.1q 
framing
(1500 byte + 4 byte vlan tag).

Erik"


My Reply:

Erik: 

The reason I am changing the MTU setting is that I am unable to properly
communicate between
domU and dom0 do to packet truncation. These errors show up when diagnostic
logging is set to maximum.

This is apparently a known issue with Xen from what I was told.

Also, my internet connection is now about 6 times as fast with 1/3 the latency
that it
used to have. I use a cable internet connection.

   
 Please see this article
 
http://www.webservertalk.com/archive236-2004-5-193783.html
     
 Bellow are the steps I used to setup FreeNX /SSH -Y--Xnest setup.
 This problem is cured by changing my MTU size.
 _______________________________________________
 I tried to get FreeNX working and was getting sigterm 15 error. Which noone was
able to help with. I decided to troubleshoot the problem by just connecting thru
SSH -Y connection from dom0 to domU. The image for the guest was created in qemu
and the system partition was migrated to a raw partition for use with Xen. I
have spent two weeks troubleshooting it and no luck. I have reinstalled openssh
and its dependents on both domU and dom0 and still no luck at all. I am at my
wits end with this problem. I have spent about 12 hours with people from the
#linuxhelp #fedora from freenode and irc.oftc.. and noone has been able to
help.. They think its a Xen issue but I am not sure. Next I was going to try and
get it working from dom0 to the qemu image to see if it made a difference.
 
 Here is the details
 
 trying to setup xnest session to remotely launch xterm (later on I would like
to get gnome working remotely)
 
 on the server side I have IP! address 192.168.15.101
 on the client side I have IP address 192.168.15.100
 
 I am not using DNS
 
 I launch the SSHD with the command /usr/sbin/sshd -d -p 1236
 
 It says
 
 debug1: sshd version OpenSSH_4.2p1
 debug1: read PEM private key don! e: type RSA
 debug1: private host key: #0 type 1 RSA
 debug1: read PEM private key done: type DSA
 debug1: private host key: #1 type 2 DSA
 debug1: rexec_argv[0]=''/usr/sbin/sshd''
 debug1: rexec_argv[1]=''-d''
 debug1: rexec_argv[2]=''-p''
 debug1: rexec_argv[3]=''1236''
 debug1: Bind to port 1236 on 192.168.15.101.
 Server listening on 192.168.15.101 port 1236
 
 On the client I issue  xhost +
 
 It says
 
 access control disabled, clients can connect from any host
 
 I type Xterm
 
 an Xterm session starts
  
 In the Xterm session I type
 
 Xnest :1 -ac &
 It informs me
 Could not init font path element /usr/X11R6/lib/X11/fonts/TT! F/, removing from
list!
 Could not init font path element /usr/X11R6/lib/X11/fonts/CID/, removing from
list!
 
 I hit <enter>
 
 A prompt appears
 
 I type ssh -Xvvv -p 1236 hikenboot@192.168.15.101
 
 It tells me
 
 It says a bunch ! of stuff
 then It says 
 debug3:authmethod_is_enabled password
 debug1: Next authentication method: password
 hieknboot@192.168.15.101''s password:
 
 I type my password
 
 It says a bunch of stuff then it says
 debug1: Recieved SIGCHLD.
 
 and then a prompt appears
 
 I type export DISPLAY=192.168.15.100:1
 
 then I type
 xterm
 
 the last lines on the server say
 
 debug1: session_new: session 0
 debug1: session_open: channel 0
 debug1: session_open: session 0: link with channel 0
 debug1: server_input_channel_open: confirm session
 debug1: server_input_channel_req: channel 0 request x11-req reply 0
 debug1: session_by_channel: session ! 0 channel 0
 debug1: session_input_channel_req: session 0 req x11-req
 debug1: channel 1: new [X11 inet listener]
 debug1: channel 2: new [X11 inet listener]
 debug1: server_input_channel_req: channel 0 request pty-req reply 0
 debug1: session_by_channel! : session 0 channel 0
 debug1: session_input_channel_req: session 0 req pty-req
 debug1: Allocating pty.
 debug1: session_new: init
 debug1: session_new: session 0
 debug1: session_pty_req: session 0 alloc /dev/pts/1
 debug1: server_input_channel_req: channel 0 request shell reply 0
 debug1: session_by_channel: session 0 channel 0
 debug1: session_input_channel_req: session 0 req shell
 debug1: Setting controlling tty using TIOCSCTTY.
  
 on the clients xterm /xnest session it just hangs!
 
 thats it..
 
 ____________________________________________________-
 

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J D Freeman

2005-Dec-21 00:57 UTC

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Re: [Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces

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Hash: SHA1

On Tue, Dec 20, 2005 at 08:58:25AM +0100, Erik wrote:> Steven,
> 
> Why would you want to change the MTU, som applications won''t like
a non standard (<1500) MTU, we use a MTU of 1504 on our 802.1q interface (an
e1000)
> in Dom0 to bridge vlan interfaces to domU and preserve a 1500 byte mtu, mtu
1504 should work without setting it as the kernel support 802.1q framing
> (1500 byte + 4 byte vlan tag).

The main reason you would want to lower the MTU like this is when using
something like PPPoE as part of an ADSL router.

If you have the right settings in iptables, linux doesn''t care about
the
lower MTU.

HTH

J
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Xen users - Dec 2005 - MTU-1492 Permenent Setting for Xen Specific Interfaces

[Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces

[Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces

Re: [Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces

[Xen-users] Re: MTU-1492 Permenent Setting for Xen Specific Interfaces

Re: [Xen-users] MTU-1492 Permenent Setting for Xen Specific Interfaces