Need help on a trunk link.

gfyrasng

Kreken wrote: »

Can you try to configure port speed and duplex instead of leaving it on auto?

Been there done that got the shirt AND the coffee mug

networker050184

gfyrasng wrote: »

Yes, but also keep in mind, the 3550XL defaults to ISL trunking and does not know what DTP is. So with both a blank config, and modifying it for 802.1Q trunking (with the other side set to non negotiate) the link still fails to establish.

It should at least see an up/down or something. Sounds like hardware issue to me.

gfyrasng

The only thing I can think of is that maybe some how the physical ports are incompatible. The ports work fine when connecting from the 2950/3550XL to the 3500, just not between each other.

networker050184

Even so it should at least give you an up/down with a blank config regardless of compatibility and I've had plenty of 3500XL switches connect to modern switches and work just fine.

At this point I'd blank the config, reboot and try again with a factory default.

I'd also quadruple check that you are using a crossover cable.

creamy_stew

I'm thinking it's an autoneg issue. Have you tried hard coding speed+duplex?

ThunderPipe

Wow. That was fun to read. As I think someone else mentioned, have you tried either:

A. Erasing Configs on both switches
B. Erasing all configs for the particular ports

This way you can narrow it down to a hardware issue or possible config issue. For it to say down/down....I'm gonna go with hardware. Cable proven to be good. Multiple ports. Hmmmmm... Thats weird. This is fun though, no?

[EDIT]
Oooh. Somehow i missed that you indeed did do this...my mistake.

Legacy User

It first sounded like it could be a port-security issue was hoping to see an err-disabled on one of the switches connected interfaces. You are dealing with switches so troubleshoot it from Layer 1 - 2. From the not-connect msg on the switch it has to be an physical/hardware issue. I'd say check if its the right cable. I know on another board some guy had an issue with his serial cables showing disconnect on one router. After everyone was insisting to check if the serial cable is connected correctly the person said it was. Long story short after days of trying to figure out the problem he posted the head of the cable was somehow connected upside down. Point is make sure everything is what you say it is to avoid any silly mistakes or wasting any additional time.

If you aren't using a crossover cable connecting to the 3550 wouldn't work though the auto-detect for cables is featured on the 3560s and newer switches. Idk..sounds like it an encapsulation issue to me. Copy and paste the configs on notepad then try an erase startup-config and delete vlan.dat. Would you by any chance have an ethernet loopback plug to plug into the problematic switches? Can you double check your duplex and speed make sure its what you say it is. Hardcode those settings in the 2950 and 3500xl then close the port then reopen them.

Legacy User

If its none of the things I mentioned next step is to throw it out of the window

creamy_stew

dmarcisco wrote: »

Idk..sounds like it an encapsulation issue to me.

Why? Elaborate.

gfyrasng

dmarcisco wrote: »

It first sounded like it could be a port-security issue was hoping to see an err-disabled on one of the switches connected interfaces. You are dealing with switches so troubleshoot it from Layer 1 - 2. From the not-connect msg on the switch it has to be an physical/hardware issue. I'd say check if its the right cable. I know on another board some guy had an issue with his serial cables showing disconnect on one router. After everyone was insisting to check if the serial cable is connected correctly the person said it was. Long story short after days of trying to figure out the problem he posted the head of the cable was somehow connected upside down. Point is make sure everything is what you say it is to avoid any silly mistakes or wasting any additional time.

If you aren't using a crossover cable connecting to the 3550 wouldn't work though the auto-detect for cables is featured on the 3560s and newer switches. Idk..sounds like it an encapsulation issue to me. Copy and paste the configs on notepad then try an erase startup-config and delete vlan.dat. Would you by any chance have an ethernet loopback plug to plug into the problematic switches? Can you double check your duplex and speed make sure its what you say it is. Hardcode those settings in the 2950 and 3500xl then close the port then reopen them.

It's not port security as there isn't any setup on these. Physical layer is good to go. I've used multiple crossover cables and multiple ports. I can take any of the same ports and cables and connect them to my 3550 and the links come up fine for both switches. The only incompatibility I've found is with trunk negotiations. The 3500xl doesn't support auto negotiation, so the DTPs have to be disabled on the 2950. I'm going to wipe both switches (again) tonight and mess around with it some more. Any suggestions for useful debug commands?

luberguilarte

It could be a port-security issue , if you used that port before as an access port and did not removed port-security when the other switch connect to that link it will create a problem , and maybe is not even showing it on the running-config , make sure you disable it shutdown the port and enable it again.

Legacy User

Port-security doesn't have to be setup to shut down the interface. If certain things don't match up I've seen port-security shut down the port to prevent damage.