For those of you using mrtg to log traffic trough your switch, I have noticed that when traffic exceeds 100mbps on a given port then by default the counter mis-reports the throughput. In order to resolve this you need to edit the config file for the associted port and switch.

This issue is due to a lack of support for snmp version 2 by default. To enable snmp version 2 in mrtg you need to edit the config filesas show below. ( I think the switch has to support this too but I am not sure about that yet)

In the config file for the switch usually found in /etc/mrtg/switch-name.cfg
(in ubuntu 10.04LTS) there will be the following line for each port on that switch

Target[]: #A1ublic@

In order to make it snmp version 2 compatible then you will need to add ::::2 to the end of each like that runs at 1Gbps so the line will look like this

Target[]: #A1ublic@

Hope that helps some people