802.1p on Cisco 2900 XL

[michaelwar]

We have a 2900 XL switch that has some servers connected to it as well as 3 hubs and 1 other 2900 switch.
I want to use 802.1p priority for our critical servers.
If I put prioritisations on the main servers would this then affect the uplink ports, should I add port prioritisation to them?..at present all are set to 0


Any help would be appreciated.

the 3 hubs and 1 switch are all connected via cross over cables and the ports set to auto duplex, auto speed and port fast enabled. Are these the best settings for uplinks?

Thanks

Mike

 

[ADB100]

To enable 802.1p priority the packets must enter the switch 'tagged' with an 802.1q header as the 802.1p priority field is contained in this header. If the NICs on your servers support 802.1q VLANs and 802.1p priority you could try that, the config on the switch would be:

interface fastethernet0/1
switchport mode trunk
switchport encapsulation dot1q

On your server you would need to set the VLAN the same as your clients - I think with Intel & Compaq/HP NICs you can add VLANs and they appear as virtual NICs, you would need to disable IP etc on the 'Parent NIC' and just use the 'Virtual NIC'. Obviously then you would set the server to set 802.1p values (0-7) for outgoing packets.

Far easier would be just to set the switchport priority to any value between 4 & 7. The 2900XL have 2 queues - CoS 0-3 map to queue#1 and CoS 4-7 map to queue#2. There is no strict priority queueing etc. I would just set the switchport interfaces default CoS to 4:

interface fastethernet0/1
switchport priority default 4


If this is part of a bigger network then you would need to look at each piece of equipment data is potentially passing through and understand the QoS capabilities in each. It is fine setting QoS up on one switch, but if you then connect to another switch and this handles QoS in a different way then the chances are your QoS polcies are redundant.

What is the reason you want to prioritise traffic from/to these servers?

Andy

 

[michaelwar]

Thanks for the help.

I think the switch option is the far easier.

I basically have a Cisco 2924 switch which has 2 other switches (both cisco 2950s) uplinked to it. And also 3 hubs.
The 2924XL has our main buisiness server on it as well as some other less used ones.
I want to ensure that any data between any user and our main business system takes priority over everything else. Occasionaly we get glitches where users can get disconnected. So i wish to put level 4s on the uplink ports to this switch and also level 4 on the port which has the main business system. My understanding is that by doing this any data on the switch destined for an uplink or the main server will take priority over anything else on the switch?...am i right?

Thanks

Mike

 

[ADB100]

Let me see. You want data to and from your main business server to have a higher priority than any other data? If this is the case then the 2924XL is not really the switch to use. The 2950's offer much better QoS - you can write an ACL that identifies traffic to/from this servers IP address (or layer-4 port numbers if you know what the application uses) and attach a DSCP, IP Precedence or CoS value to these packets. These packets can then be scheduled into a high priority queue on the Egress interface (uplinks). The 2950 can do this, but the 2924XL cannot as it only understands Layer-2 CoS values in 802.1q or ISL encapsulated frames. The 2924XL only have 2 WRR egress queues also, whereas the 2950 has 4 WRR queues, one of these can be configured as a Priority queue and will take precedence over all other queues (usually for Voice RTP Packets).

Andy