Client requests fail when Load Balancer attempts to return large page responses
 Technote (troubleshooting)
 
Problem(Abstract)
Client requests that result in large responses timeout if the maximum transmit unit (MTU) is not set properly on the Load Balancer machine. This can occur because Load Balancer defaults the MTU, rather than negotiate it, for Dispatcher component's CBR and NAT forwarding methods.
 
Cause
The MTU is set on each operating system based on the communication media used; for example, Ethernet or Token-Ring. Routers from the local segment might have a smaller MTU set if they connect to a different type of communication media. Under normal TCP traffic, an MTU negotiation occurs during the connection setup, and the smallest MTU is used to send data between the machines.

Load Balancer does not support MTU negotiation for Dispatcher's CBR or NAT forwarding method because it is actively involved as an endpoint for TCP connections. For CBR and NAT forwarding, Load Balancer defaults the MTU value to 1500. This is the typical MTU size for standard Ethernet, so most customers do not need to adjust this setting.
 
Resolving the problem
When using Dispatcher's CBR or NAT forwarding method, if you have a router to the local segment that has a lower MTU, you must set the MTU on the Load Balancer machine to match the lower MTU.
Use the following command to set the MTU value:

dscontrol e xm 32 <new_value>

For example:
dscontrol e xm 32 1400
You do not need to modify the MTU for Dispatcher's mac forwarding method or any non-Dispatcher component of Load Balancer.
 
 
Cross Reference information
Segment Product Component Platform Version Edition
Application Servers WebSphere Edge Server Load Balancer Multi-Platform Edge Server 2.0 GA, Edge Server 2.0 NLV, Edge Server 2.0.x
Application Servers Runtimes for Java Technology Java SDK
 
Historical Number
249946
 
 


Document Information


Product categories: Software > Application Servers > Distributed Application & Web Servers > WebSphere Application Server > Edge Component
Operating system(s): Windows
Software version: 6.0.1
Software edition:
Reference #: 1198181
IBM Group: Software Group
Modified date: Feb 14, 2005