cisco 2948G & 2900XL

[circut16]

for some reason i do not know the network starts broadcasting everything to all the ports.
It doesn't do this all the time either.

If anyone else out there knows any pointers to give this cisco noob please don't be shy to give some suggestions.

it would make me really happy to have this hardware act like it should and not like a stupid hub.

 

[spidey07]

It's probably doing exactly what it is supposed to. But is not configured properly.

What you're describing is normal for spanning-tree and topology change notifications. The switches will dump their mac tables and flood for a period of time. Make sure all ports that are connected to hosts (not other switches) are using spanning-tree portfast feature. You can also look at spanning-tree statistics for each particular vlan to see when the last TCN has occured.

search cisco.com for "troubleshoot spanning-tree" for tons of information.

Also understand that broadcasts are always flooded to every port in that vlan, so if it's a trunk port it is going to send any broadcast for any vlans that are in a forwarding state for that trunk. multicast frames are also flooded unless multicast features are used (IGMP snooping or CGMP)

-edit-
read each and everyone of these. Understanding spanning-tree is crucial to understanding lan switching.
http://www.cisco.com/en/US/tec...ng_technotes_list.html

 

[circut16]

how often do topology change notifs occour (it hardly ever shanges)
but there are 2 3com switches too - i'll just be downloading a file and the traffic is flooding on all the switches - aside fron normal broadcast paterns this one really stands out.
I'm not using any STP but do have some crossover cables and fiber connecting them all.
spannig tree port fast? what is that

 

[spidey07]

3com switches were notorious for just up and flooding traffic for no good reason.

TCN happens whenever a port moves from forwarding to blocking or blocking transition to forwarding.

Also how do you now you're not running spanning-tree? If so it would be in your best interest to do so, it may be possible that you have bridging loops somehow occuring. Also you can have bridging loops with fiber optic if a unidirectional link condition occurs (TX strand of fiber working, RX strand is not).

 

[circut16]

it's all a star - most of this equip is in one rack


how would stp help me - besides the reliability

i never had this happen until brought the cisco gear in the network

I appreaciate your help, is there some other config that is staring me in the face tha t should look into?

 

[spidey07]

There are so many things that can cause this it's probably best to open a TAC case.

Look in the link I posted above about TCNs and portfast. Cisco switches run generic 802.1d spanning-tree by default.

 

[circut16]

(Cisco switches run generic 802.1d spanning-tree by default)


REALLY??

wow i had no idea

thanks bro, i owe you one

 

[spidey07]

Well a switch is nothing more than a bridge, so it absolutely should run spanning-tree.

Also Cisco does a single spanning-tree for each and every vlan by default. they call it per vlan spanning-tree.

 

[circut16]

do you know of any catOS downloads anywhere? for 2948G

 

[spidey07]

Originally posted by: circut16
do you know of any catOS downloads anywhere? for 2948G

These are available from Cisco and any active maintenance on the specific 2948G in question. I cannot condone license infringement as you can take my ability to download any software no matter what from Cisco.com from my cold dead hands.

Meaning - they trust the user enough to abide by the agreement and are fairly open with their software. I'm not going to abuse that trust.

If you need the software for lab or trial use you can call them and they may allow you to download it. Any releases that address security are free no matter what maintenance you have. Hint.