Question

Collisions between Cisco 1601 and 3com Switch. THEY WON'T STOP???

Asked by: TJanousek

I have a T1 line to the Internet via a Cisco 1601 router.  From the ethernet interface, I have it going to a 3com 4400 series switch, then to my Pix firewall (I have to do it that way as I have some devices I need on the outside of the firewall and need more than one port).  My ethernet interface counts up collisions and fragments no matter what speed I set the 3com ports to.  10half or auto, neither of them work.

I'm assuming the 1601 is 10base-T meaning it's 10half.  I've tried replacing the cable and also put a different switch in place, but the collisions simply won't go away.

What the heck am I missing?  Thanks in advance for the help.  Here's the config for my ethernet interface on my router

interface Ethernet0
 description connected to EthernetLAN
 ip address x.x.x.x 255.255.255.0
 no ip directed-broadcast
 bridge-group 1

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Asked On
2005-08-05 at 13:15:38ID21517507
Tags

3com

,

1601

,

cisco

,

switch

Topics

Miscellaneous Networking

,

Networking Hardware Firewalls

,

Network Switches & Hubs

Participating Experts
4
Points
110
Comments
10

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Answers

 

by: photograffitiPosted on 2005-08-05 at 13:31:20ID: 14611326

With half-duplex you will always have collisions. That's just the nature of the technology. As long as there aren't late collisions or excessive collisions, you should ignore it. Are you running into a specific issue?

 

by: TJanousekPosted on 2005-08-05 at 13:36:11ID: 14611362

I would say they are extremely excessive.  I have 6200 in the last 15 minutes or so (collisions that is)

 

by: photograffitiPosted on 2005-08-05 at 13:41:39ID: 14611392

6200 out of how many packets in the last 15 minutes? The ratio is important to see if it is a problem. Also, have you checked to see if the 3COM switch ports is also configured for half-duplex? If the router is half and the switch is full, that will definitely cause your high collision amounts.

 

by: TJanousekPosted on 2005-08-05 at 13:44:04ID: 14611408

5 minute output rate 744000 bits/sec, 105 packets/sec
     130807 packets input, 54425105 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 input packets with dribble condition detected
     149309 packets output, 119322928 bytes, 0 underruns
     0 output errors, 7406 collisions, 1 interface resets
     0 babbles, 0 late collision, 1825 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out

I'm also going to try a different router (hopefully if I can get a 2600 series by this weekend) and try setting both ports to 100full.  

Our Internet speeds are terrible, I'm assuming it's because of the collisions.

 

by: photograffitiPosted on 2005-08-05 at 13:50:18ID: 14611471

You're at 5% collisions, which is still within generally accepted standards. However, if you think it is affecting your Internet connection (which it shouldn't) then going to a full duplex connection should help.

 

by: Danny_LarouchePosted on 2005-08-05 at 15:26:24ID: 14612205

Maybe MTU on the 1600 and the PIX doesnt match causing a ICMP message that cause the collision. The rejected packets (announce by the ICMP packets) have to be resend and slow down the effective bandwitdth on the network.  

Did you tried (for testing purpose) to connect the 1600 and the pix directly without the switch to see if collision still occure? Using fater NIC on servers tend to cause more collision when mixed with slower ones.

 

by: Danny_LarouchePosted on 2005-08-05 at 15:31:33ID: 14612230

Oooopps forget  second part of my message concerning NIC`s speed. In fact interface`s speed is not involved in collision because they are switched!!

 

by: lrmoorePosted on 2005-08-06 at 07:02:32ID: 14614176

photograffiti is 100% correct. 5% collisions is not an issue.
Collisions are inherent to the technology in any half-duplex environment. 10% of traffic being collsions becomes a concern point.
Cisco and 3COM don't make good neighbors - long history of interoperability issues. Best setting on the switch is 10/half
1600 router is end-of-lifed and you should be considering a replacement anyway. One that has full-duplex capabilities

 

by: keith_alabasterPosted on 2006-01-05 at 15:10:55ID: 15624342

No comment has been added to this question in more than 21 days, so it is now classified as abandoned..
I will leave the following recommendation for this question in the Cleanup topic area:

Accept Photograffiti & lrmoore

Any objections should be posted here in the next 4 days. After that time, the question will be closed.

Keith_Alabaster
EE Cleanup Volunteer

20120131-EE-VQP-002

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