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CentOS 5.2 & Configuring MTU

July 21, 2008 By: HKP30 Category: CentOS, Networking 3450 Comments →

ifcfg-eth0 configuration example

We have one server in our office that performs very few functions.  In fact its lone reason for being on the network is to allow one of our customers to GET and POST data into the lease management system the company I work for runs.  The customer requested some kind of web server to manage the GET and POST procedures.  We established a site to site VPN, secured access to and from the LAMP server between four hosts on their network (two development, one production, and one disaster recovery) and our LAMP server.  (It’s named LAMP.  It also happens to be a L.A.M.P. server)

All seemed to be working well.  Until at some point the customer noticed that certain types of traffic just didn’t work to/from the server.  As it turns out because of the IPSEC VPN, and encapsulation we needed to adjust the MTU on both ends of the link.

If you are ever using a CentOS 5.2 server, and you want to adjust the MTU to something other than the default with that change surviving reboots of the server you need to do the following.

vi /etc/sysconfig/network-scripts/ifcfg-(interface)

add a line that reads.

MTU = (some number less than 1500 here)

save and exit the file.  Now if you would like to make that change take effect right away.  You can either…   /etc/init.d/network restart  OR….  ifconfig (interface) mtu (some number < 1500)

Clear as Mud eh?

ifconfig post restart

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