Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Need help to configure qos on catalyst 2950


My name is Serge DIAI and i'm a head manager in technical support in a company in morroco.

One of our activities is based on voip.

In our infrastructure we have our own switch catalyst 2950 and router cisco 1812 managed by the FAI.

On the catalyst we haved switched 2 server IPBX ASTERISK ,A voip gateway (QUINTUM) and the router CISCO.

I want to configure  qos of voip at the catalyst interface (F0/23) wich is connected to the router cisco or in general in the catalyst to  give preferential treatment to voip traffic to resolve some problem when congestion occurs.

Is that possible?

Can you help me

Thank you for your attention


Re: Need help to configure qos on catalyst 2950

Re: Need help to configure qos on catalyst 2950

To add to Glens post (great link BTW), are you sure there is contention on the link between the router and the switch? I would double check speed and duplex and make sure they match and that there are no errors on the interfaces.

New Member

Re: Need help to configure qos on catalyst 2950

Thanks for your response.

To answer to glan, i have already seen the link and read this chapter.

But I don't know for my case what model i have to choose. (voip traffic using  SIP, H323 and IAX protocol on my LAN) and I dont use cisco ip phone but softphone such as pangolin, eyebeam.

And to answer to collin., i want to do this because 1st we use the same Link WAN on the router for voip and data.

So sometimes we have some noise or some "hatching" (don't know if it's the good term in english) likes robot voice.

And in this case when I check the catalyst interface connected on the router in general I don't see errors on CRC but bandwich used in input and output is high.

For example:

CATALYST2950#show ip traffic
IP statistics:
   Rcvd:  12807967 total, 2622166 local destination
          0 format errors, 0 checksum errors, 0 bad hop count
          0 unknown protocol, 10185801 not a gateway
          0 security failures, 0 bad options, 22986 with options
   Opts:  0 end, 0 nop, 0 basic security, 0 loose source route
          0 timestamp, 0 extended security, 0 record route
          0 stream ID, 0 strict source route, 22986 alert, 0 cipso
          0 other
   Frags: 0 reassembled, 0 timeouts, 0 couldn't reassemble
          0 fragmented, 0 couldn't fragment
   Bcast: 2591021 received, 3 sent
   Mcast: 0 received, 0 sent
   Sent:  111960 generated, 0 forwarded
   Drop:  1595 encapsulation failed, 0 unresolved, 0 no adjacency
          0 no route, 0 unicast RPF, 0 forced drop
   Drop:  0 packets with source IP address zero

ICMP statistics:
   Rcvd: 0 format errors, 0 checksum errors, 0 redirects, 1 unreachable
         3274 echo, 0 echo reply, 0 mask requests, 0 mask replies, 0 quench
         0 parameter, 0 timestamp, 0 info request, 0 other
         0 irdp solicitations, 0 irdp advertisements
   Sent: 0 redirects, 0 unreachable, 0 echo, 3274 echo reply
         0 mask requests, 0 mask replies, 0 quench, 0 timestamp
         0 info reply, 0 time exceeded, 0 parameter problem
         0 irdp solicitations, 0 irdp advertisements

UDP statistics:
   Rcvd: 2591129 total, 0 checksum errors, 2591129 no port
   Sent: 82636 total, 0 forwarded broadcasts

TCP statistics:
   Rcvd: 27873 total, 0 checksum errors, 0 no port
   Sent: 26054 total

ARP statistics:

  Rcvd: 13742785 requests, 1975 replies, 0 reverse, 0 other

  Sent: 5217 requests, 8860 replies (0 proxy), 0 reverse

CATALYST2950#sh int f0/23

FastEthernet0/23 is up, line protocol is up (connected)

  Hardware is Fast Ethernet, address is 0014.6a44.1817 (bia 0014.6a44.1817)

  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

     reliability 255/255, txload 3/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex, 100Mb/s, media type is 100BaseTX

  input flow-control is unsupported output flow-control is unsupported

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:29, output 00:00:00, output hang never

  Last clearing of "show interface" counters never

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 542000 bits/sec, 864 packets/sec

  5 minute output rate 1429000 bits/sec, 1994 packets/sec

     892958707 packets input, 426096684 bytes, 0 no buffer

     Received 85795 broadcasts (0 multicast)

     0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 84702 multicast, 0 pause input

     0 input packets with dribble condition detected

     1952507841 packets output, 640219550 bytes, 0 underruns

     0 output errors, 0 collisions, 2 interface resets

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 PAUSE output

     0 output buffer failures, 0 output buffers swapped out

Re: Need help to configure qos on catalyst 2950

I'm pretty sure those are accumulated numbers. Under the interface you can see the load-

txload 3/255, rxload 1/255

poor mans way of calculating-

3/255*100=1.2% utilization

1/255*100=0.4% utilization

To implement QoS, the link that Glen provided should provide a good framework. You may have to mark the traffic as it come into the switch, it depends if your applications already mark their traffic. Another good QoS reference is the SRND-