We have a core network comprised of 6509's Sup2/MSFC2. These are our core switches but also our distribution routers....
Long story short, hanging off these 6509's we have servers, softswitches, IP PBX equipment, lots of other connections coming in from remote pop's, ADSL equipmnet (7206VXR's) etc. etc...
What I've setup so far is NBAR on a couple of VLAN interfaces to mark RTP, SIP and MGCP:
class-map match-any QOS-VOIP
match protocol sip
match protocol rtp
match protocol mgcp
set dscp cs5
set dscp default
Then on the VLAN interface I have:
service-policy input QOS
I can't apply outbound service-policy but as I understand QOS and VLAN interfaces, I'm really applying CS5 to traffic leaving this VLAN anyways which is what I want....
Now that I have marked this traffic, how do I tell the other cards/interfaces within this chassis to apply priority in the queueing? This is kind of sparked as well by the older cards in this chassis and would rather not replace cards if it can be avoided - but will if neccessary...
Thanks.. I had already read most of that (maybe too fast) plus have my trusty "End-to-End QOS Network Design" book from Cisco Press... good read...
Because there seem to be so much to take in, what I'm looking for is a clearer understanding of how to prioritize on interfaces within the 6500 itself. We have ZERO congestion - I just want to provide priority....
Right now I have applied numerous NBAR based rules to give voice traffic DSCP EF at this point (rtp, sip, mgcp specifically) and now I need to ensure the queues on interfaces let these packets through first everytime... how do I do that (or really, what's the best way) is probably the best question?
I know you have already been referred to the Enterprise QoS SRND. For 6500's the best section of the guide is "Catalyst 6500 - Queuing and Dropping"
Here is what we do on our Catalyst 6500's. My line card is a WS-X6748-GE-TX with 1p3q8t. This means I have 4 queue, 1 of which is the priority queue. Queues 1-3 are regular queues, 4 is the priority queue.
The size of each queue is set with the command "wrr-queue queue-limit 5 25 40". This assigns the % of buffer space (in my case 1MB buffer) to each of the queues. 5% to queue 1, 25% to queue 2, 40% to queue 3. This totals 70%, the remaining 30% is automatically assigned to the Priority Queue.
I will skip the "wrr-queue random-detect" commands. They are for weighted random drops of packets, but only matter when an interface is congested.
Packets are mapped to a queue with "wrr-queue cos-map A B C" where A=queue#, B=Threshold, C=COS value.
queue 1 services COS 1
queue 2 services COS 0
queue 3 services COS 4,2,3,6,7
queue 4 (priority) COS 5
The 6500 does some funny things with COS and DSCP values. This makes the "mls qos trust" and "mls qos map".
Internally, the 6500 assigns DSCP values to packets for queueing. It uses mls qos trust and mls qos map to determine the internal DSCP mapping. You can see the maps with "show mls qos map".
If an interface is set to "mls qos trust", the switch will accept the assign value (cos, dscp, IP Prec) and re-write the corresponding DSCP value. If I trust cos and a packet is marked with COS 5, the mls qos map cos-dscp command maps the packet with DSCP 46 (EF).
The map assigns a DSCP value for each COS value.
**COS Value*** 0 1 2 3 4 5 6 7
mls qos map cos-dscp 0 8 16 24 32 46 48 56
Here is the problem to watch out for; if an interface has "mls qos trust cos" and packets come in without COS marking, but they have DSCP markings, the switch re-writes the DSCP value to 0.
The only time I trust COS is when an IP phone is connected to the port. If packets are marked with DSCP then trust DSCP.
I did have a problem on a Catalyst 3750 were I trusted DSCP, but upstream the packets were marked with IP Prec. DSCP CS5 is supposed to be the same as IP Prec 5, but the switch was marking all the IP Prec packets down. I changed the trust to IP Prec and all was good.
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