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PC slow when connected to Cisco IP Phone

Users are complaining that their PCs are slow when connected to the network through Cisco IP phone. Speed is regular when PC is plugged directly to the network switch. Access switches where IP phones are connected are mostly Cisco WS-C3560-48PS. Most of the phones are 7942G There is no local Call Manager. CCM is reachable over the MPLS. Latency less than 10ms

Any ideas what problem could be?


Access-SW01#sh run int Fas 0/16 

interface FastEthernet0/16
 switchport access vlan 128
 switchport mode access
 switchport voice vlan 129
 srr-queue bandwidth share 10 10 60 20
 priority-queue out
 mls qos trust device cisco-phone
 mls qos trust cos
 auto qos voip cisco-phone
 spanning-tree portfast
 service-policy input AutoQoS-Police-CiscoPhone


Access-SW01#sh int Fas 0/16

FastEthernet0/16 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0026.cad0.5792 (bia 0026.cad0.5792)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 10/100BaseTX
  input flow-control is off, output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:44, output 00:00:00, output hang never
  Last clearing of "show interface" counters 1y7w
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 5417
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 1000 bits/sec, 1 packets/sec
  5 minute output rate 7000 bits/sec, 8 packets/sec
     83500725 packets input, 51399423374 bytes, 0 no buffer
     Received 1174461 broadcasts (850091 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 850091 multicast, 0 pause input
     0 input packets with dribble condition detected
     304310331 packets output, 84586626038 bytes, 0 underruns
     0 output errors, 0 collisions, 0 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



interface Vlan128 - data vlan
 description Office VLAN
 ip address
 ip helper-address
 ip helper-address
interface Vlan129 - voice vlan
 description IPT VLAN
 ip address
 ip helper-address
 ip helper-address




Stephen Welsh

Have you checked on the phone side to see what it has negotiated with the PC, a common issue is when the wrong duplex is negotiated between the Phone and the PC.

A customer of ours recently resolved PC-Phone issues using PhoneView from UnifiedFX, the paid for product provides full endpoint management, however the free ITL Scanner also performs phone inventory, the data gathered includes a number of PC/Switch port CDP datapoint that should help to resolve this issue.

The free phone inventory functionality is included in the ITL Scanner:

This works for up to 10,000 phones, if you have more phones you would need to buy a license.


PhoneView is now Cisco Compatible, the only product in it's category to pass IVT testing.


Kind Regards


Stephen Welsh






Are you trying to sell me something?

Ironically no, the free software should be all you need.


Did you resolve th issue?

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