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New Member

Intermittent connectivity in single vlan

Hello, I have this problem: In one of cca 200 Vlans on network, there is sometimes intermittent connectivity. The outage is about 1-3 s long, once per cca 30-60s -random. Userc can not neither ping their default gateway nor other users in vlan. This occurs on one vlan on multiple switches, others vlans not. Affected are all users, apart where they sits. Network design is following: Two C6500(SUP2,MSFC2,PFC2) in core, connected with fechannel.They are running HSRP. Acces switches are C5000, connected with FE trunk. I have tested debug standby terse on msfc with no output.I think hsrp is ok. In logging buffer of access switches, there are no messages indicating port problems. End stations are connected with 10M/h-dx. Can You help me, please?


Re: Intermittent connectivity in single vlan


This is an intresting case. I have a few possible causes you can try out.

Are you running Netware?

1: Might be a broadcast issue that fills up the vlan. This may very well be possible in a large network with 10 and 100Mb. One thing that points in this direction is the 30-60s interval, which coincides with the RIP / SAP update interval.

2: You might be running out of mac adresses now and then on some of your hardware. Not likely when you are only using 6500 and 5000 switches.



New Member

Re: Intermittent connectivity in single vlan

I am assuming there are multiple vlans. Make sure the root bridge for any vlans is the cat 65xx. In addition look out for spanning tree loops.

The C5000 switches, since they are edge, should/can be multi-homed to the core...but if you have the c5K connected to each other, once again spanning tree issues may arise.

Hardcode the spantree roots using:

set spantree root

See if this works.

New Member

Re: Intermittent connectivity in single vlan


my problem is solved. Problem was caused by IPX broadcast traffic, leaking from one vlan to another. I have found two access switches, with ports connected to each other. Ports were in different vlans, so traffic from one vlan was leaking through network to core switches making problems all around.

Thanks for Your support and i wish many health to Your networks. S.J.