3750 to 2950?

Unanswered Question
Feb 15th, 2007


we've recently done some restructuring on our network and the 2950 in our room is now fed from a 3750 switch (instead of another switch we had) and since then the management on the 2950 seems to be dropping off all the time. network connectivity would remain perfectly stable.

is there any config that we may have overlooked on the 3750 that could cause the management on the 2950 alone to be intermittent?


I have this problem too.
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glen.grant Thu, 02/15/2007 - 20:00

Haven't heard of anything like that . Check the configs on each end , if they are just access ports make sure they are configured the same , if trunks make sure they are configured the same on both ends . might want to check for any bugs for the codes you are running .

spremkumar Thu, 02/15/2007 - 20:22


In addition to Glen's comments i would also suggest to check out the default gateway in your Cisco 2950 switch which may be pointing towards the old switch's ip address..


redsupra101 Thu, 02/15/2007 - 20:31

all switches on the network point to one dhcp server and one default gateway, so im not sure that may be the issue.

normally when doing these changes during relocation, all that needs to be done is ensure that the ports are configured as auto negotiate (that defaults to 100/full) and are set as trunk ports with the needed vlans.

the part that has me confused is that only the management ip address is intermittent and the network connectivity from both the 2950 and the 3750 is working flawlessly.

and of course, with the management being intermittent, we cant remotely configure the switch, so it's growing to be a pain, especially when your email is being overfilled with the email alerts for the switch's 'downtime'

the switch was rebooted just to see if that would help (the 2950 that is) but that didnt help a bit.

and this problem ONLY started when the switch was moved from being fed by another brand of managed switch to the new 3750.

glen.grant Fri, 02/16/2007 - 04:37

Unless you getting someone who is putting a duplicate address on the network that matches the 2950 , that would cause intermittent problems .

redsupra101 Thu, 02/15/2007 - 20:46

they are trunks, and both are config'd as trunks with the management vlan tagged to the port.

like i said, connectivity is 100% up, so i dont think that's a vlan or trunk/access port config error... but im not the smart one here so im open to suggestions of course :)


rduke Sat, 02/17/2007 - 17:49

Which model of 3750 and 2950 are you using ? Are you using gigabit? I have a number of 2950T switches with gigabit links to 3750G models- no problems at all, but I had serious problems with old hubs plugged into the 10/100/1000 ports on a 3750. They flat would not work. They were also intermittent.

Anyhow, you can see if there are any temporary drops in each vlan by turning on spanning-tree debugging

debug spanning-tree events


debug spanning-tree pvst+


You don't have VLAN pruning enabled do you? That got me in to trouble once so I don't like using automatic pruning now.

I have a dedicated VLAN for network management on all of mine.


redsupra101 Mon, 02/19/2007 - 16:00

we did not change the ip of the catalyst 2950 after the change and again the only change made was it was moved from being fed by an enterasys v2 switch to the new cisco 3750

its fed from a fastethernet port on the 3750 to a gigabitethernet port on the 2950.

the LAN connectivity and management have their own dedicated vlans, so its just the management vlan that is 'dropping off' as Lan connection remains up 100%.

I thought that maybe because it was going from a fa port on the 3750 to a gi port on the 2950 that might have been the problem.. but both ports are set to auto-negotiate so it should default to 100/full anyway, and besides it was fed this way off the old enterasys switch as well (from fa on enterasys to gi on cisco)

balajitvk Mon, 02/19/2007 - 20:08


Could u post the configs??? I don't think that could be the reason fa port to gi port... becz it should affect your data vlan too.....


redsupra101 Mon, 02/19/2007 - 20:37

i'll TRY TO post the configs when i get back to work, no remote access to the switch since i dont have connectivity to it over the management vlan. (same problem im trying to fix!)


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