Cisco Catalyst bottleneck

[rlif]

I have a very simple LAN. I use a Cisco 24 port Catalyst switch (with the default configuration) to connect my network devices. On port 1 is my 6 Meg Internet connection. On port 3 is a firewall with 1 server behind it. On ports 4 and 5 are Cisco 5300’s each doing 4 T1s of VoIP. All other ports are empty.

The problem is this: when I add the 3rd 5300, the network slows to a crawl. On the port on which I added the 5300, the LED light cycles between blinking green then orange. When I remove the new 5300, the LAN is OK again.

The problem is not the 5300, as any 3rd Cisco causes the problem. The problem is not the Internet bandwidth, I verified this with my ISP. The problem is not throughput as each 5300 uses less than 1 Meg. The problem is not the port, as I tried others. The problem is not the Catalyst, as the same thing happens when I swap in a Cisco hub. I’m baffled!

 

[CCIEWANNABE]

Those blinking patterns tells me Diagnostics are in progress and an attempt to connect. Verify IOS in use and also check that the module's have not shifted out of its slot.
Route once; switch many

 

[scraig84]

If you are using the default configuration on the switch, this means you are using autonegotiation for port speed and duplex. This is rarely a good idea and a frequent source of problems. I would lock down both sides to the optimal speed and duplex and see if that helps. Also, have you tried plugging into multiple ports on the switch, or just 1?

 

[rlif]

I tried many ports, all OK. What do you mean by "optimal speed"?

 

[rlif]

I previously set my 5300 ports to fastport but left autonegotiate on. After explicitly setting values the problem seems to go away. Was this the problem? I do not know for sure. This kind of uncertainty never happened in the good old days of TDM.

 

[scraig84]

By "optimal speed" I mean the best possible combination based on your hardware. The best you can hope for is 100Mb/full duplex. However, if you don't have a 100Mb port on your switch or the 5300 doesn't support full duplex for example, this may not be possible. You usually want the fastest speed and full duplex if they are possible, but you have to go with what the hardware on both sides supports.

Sounds like you got it going. Speed/Duplex autonegotiation is a non-standard thing and NIC card and switch manufacturers can do things differently causing it to fail almost randomly. Cisco switches especially seem to have difficulties in my opinion, so it is typically a good idea to lock it down on both sides.

 

[wybnormal]

Scaig84 is correct and Cisco's own best practices strongly suggest to lock ports down. Our process is to lock switch ports to 10 1/2 and then bring them up one at a time. It's time consuming but I personally got badly bit during one upgrade with supposedly CAT5 cabling and more then afew stations crapped out due to shoddy wiring.

2 lessons.. never ever trust the cable vendor without a printout from EACH cable run.. and yes, they will kick, scream, cray about taking from their kids mouths and on but insist on it.

2nd lesson is to NEVER trust the autonegotiation process

MikeS
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