Change Maximum Transmission Unit Size

1	Introduction
1.1	Prerequisites
2	Procedure

1 Introduction

This document describes how to change the Maximum Transmission Unit (MTU) size.

Default is 1452 bytes, as the system internal IPv6 tunnels add an overhead of 48 bytes.

The default value works for the widest variety of available Ethernet switching infrastructure hardware and there is in general no need to deviate from the default value. Changing the value in service leads to a cluster reboot and interruption of service.

1.1 Prerequisites

This section describes the prerequisites, which must be fulfilled before using the procedure.

1.1.1 Conditions

The following conditions must apply:

The new MTU size is known.
The user has the System Security Administrator role.
An Ericsson Command-Line Interface (ECLI) session in Exec mode is in progress.

2 Procedure

Attention!

Risk of system malfunction or traffic disturbance.

Service is interrupted during a cluster reboot.

To change the MTU size:

Navigate to EvipParam managed object, for example:
>ManagedElement=NODE06ST,Transport=1,Evip=1,EvipParams=1,EvipParam=mtu
Enter Config mode:
(EvipParam=mtu)>configure
Change the MTU size, for example:
(config-EvipParam=mtu)>value=1280
Commit the setting:
(config-EvipParam=mtu)>commit
Open up a console connection to SC-1, for example:
ssh root@<hostname>
Perform a cluster reboot:
Attention!
Risk of system malfunction or traffic disturbance.

SC-1:~ #cmw-cluster-reboot

The following output is shown:
Do you really want to reboot the entire cluster (yes/no)?
Enter yes to reboot.

Verify the MTU size of the traffic interface:

SC-1:~ #ifconfig alb_tr

The following is an example output:

alb_tr    Link encap:UNSPEC  HWaddr FE-80-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:10.118.160.53  P-t-P:10.118.160.53  Mask:255.255.255.255
          inet6 addr: 2001:1b70:4292:8207::51/128 Scope:Global
          inet6 addr: fe80::3e19:7dff:fe0e:ab0c/64 Scope:Link
          UP POINTOPOINT RUNNING NOARP  MTU:1280  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:19954 errors:4 dropped:4 overruns:0 carrier:0
          collisions:4 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:9443431 (9.0 Mb)

Verify the MTU size of the authentication interface:

SC-1:~ #ifconfig alb_aut

The following is an example output:

alb_aut   Link encap:UNSPEC  HWaddr FE-80-00-00-00-00-00-00-00-00-00-00-00-00-00-00
          inet addr:10.118.160.43  P-t-P:10.118.160.43  Mask:255.255.255.255
          inet6 addr: fe80::3e19:7dff:fe0e:ab0c/64 Scope:Link
          inet6 addr: 2001:1b70:4292:8207::43/128 Scope:Global
          UP POINTOPOINT RUNNING NOARP  MTU:1280  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:232 (232.0 b)