Network Outage Due to Replacment of old switch with Newly configured Switch

[Sandeep_N21]

Hi Team,

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Recently we had an Issue were in the Entire Network was isolated due to introduction of Newly configured switch.

This was an L2 Switch which was connected to distribution switch like other user switches.

The new switch was configured and as soon as the uplinks were connected to the distribution switch the entire network was un accessible and when it was removed it came back.

Not sure why this loop has happened as we have Bpdu Filter enabled on user switches

What are the causes for this issue

[Carlos Villagran]

Hi!

This absolutely sounds like a VTP server issue. Are you using VTP in the network? Was the new switch actually new or it was used in another site and installed here?

Best regards!

JC

[pwwiddicombe]

Yes, having a pre-configured switch that has a default setup or had been used in production, can do nasty things to VTP tables, if set up this way.  It may be as simple as recreating the VLAN definition for any that are missing (if you know what they are) and verifying (and port interfaces have probably not been altered).  Although the fact that this switch being removed brought everything back to normal suggests this probably wasn't the case.

The other thing to check is that the IP address of the new switch doesn't happen to be a gateway address on the existing network.

[Sandeep_N21]

Hi,

We do not use VTP in our environment as usually everything is configured as transparent and the this was just an new switch and not used any where.. the thing is we have done this earlier also but never came across were the entire network got isolated it was just when the uplinks were connected to the newly configured switch with all configuration in place...

Thanks for your feedback

[Carlos Villagran]

Hi!

Was the configuration of this new switch different than the other access switches?

I am thinking about a possible STP loop caused by a misconfiguration in a trunk link.

Best regards!

JC

[Prabath Godevithanage]

Hi Sandeep,Do you have any logs from your distribution and access switch?Bpdu Filter woudn't save you from loops. 

[Paul Chapman]

Hi Sandeep -

I tend to believe that you put a loop in your network, because you describe the behavior as "went away" when the switch was removed.  Additionally, you used the term "uplinks", implying that you have multiple connections to the upstream switch from the one that you are installing.

Based on the description, I believe that you have misused the BPDU Filter feature and confused it with BPDU Guard.  I have seen BPDU Filter used incorrectly numerous times and it is often the cause of network loops since it effectively disables STP on a port (or globally).

I suggest that you use BPDU Guard instead along with ErrDisable Recovery.  This will give you much more predictable results when modifying your network topology.

PSC