We have a problem with Nortel IP Handsets connected to a Cisco 2960 switch. When the handset is connected to the switch it comes up with a "Server Unreachable" message. Traces taken on the network show that the handset sends it's packets tagged with A0 (DSCP CS5). This then passes through the 2960 switch and has the tagging stripped to 00. If we connect the handset to a 2950 or similar the tagging remains A0 and the IPT works okay. If we connect the handset to a 2950 switch and connect that switch to the port on the 2960 that the handset just failed to work on, it then all works okay (so direct into the 2960 you have a problem, but put a 2950 in between and it is fine)
I have erased the config on the 2960, replaced the 2960 and tried several different models (& IOS). All have the same issue.
We tried connecting to 3550 and 3560 switches and had the same problem (A0 stripped to 00). However these were EMI models with qos in the config. This was removed (no qos) and these work okay.
The default on the 2960 is no mls qos so I would have expected this switch to behave the same way.
I have tried configuring the port for all options of auto mls qos; with\without mls qos trust options; with\without no mls qos rewrite ip dscp.
I have not tried configuring up different VLAN's for voice and data (as per the example online) as we have hundreds of sites where the third party contraints is that there is only one VLAN so I have to have a solution that allows a single VLAN1 - basically to allow the 2950 series to be replaced by the 2960 series with minimum impact.