Spanning Tree Protocol blocking Network management software?

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Nov 3rd, 2008
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Hi, i have three Cisco 4507R routers and am using the 3com 3NS network management software to test out. (Which creates a network topology map and lets me monitor the network health)

All works fine except one router is always discovered but never placed on the map, if i discover again it will be placed on the map but another will be removed.

The subnets on the router that cant be found will just be orphaned at the top, the misconfiguration report says its because of the Spanning Tree Protocol blocking the link.

Is there any way around this?


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satish_zanjurne Mon, 11/03/2008 - 06:01
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OK !!

1.For some time ignore the Network Management software

2.See whether you are able to ping all routers & you are able to logon to them

3.This should help you to isolate the issue.

HTH..rate if helpful..

Giuseppe Larosa Mon, 11/03/2008 - 06:28
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Hello Jamie,

I would verify the SNMP configuration of the missing router.

Use sh snmp to see if there are communications errors.

You can also verify the STP config with

show spanning-tree on all three switches

But STP shouldn't be the reason under this problem

Hope to help


superdude5000 Tue, 11/04/2008 - 02:20
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Hi thanks for the replies so far.

I can ping all three routers and the snmp configuration is ok on all three (public and private string configured). The network management software will discover all three but wont display one on the map (but the weird part is if i scan again it will appear but remove a different one!). They are connected in a triangle so STP stops them causing a loop i guess.

What am i looking for in the STP config?

francisco_1 Tue, 11/04/2008 - 02:30
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I dont think the problem is STP. I could be wrong but if there no L2 loop on your network and your network is working ok then no need to look at your STP config but i suggest you check the logs on the switches for any logs related to STP. The problem sounds like to do wiTH your snmp software!. maybe you are using a trial version or license problem?

maybe if you have another device on the network, add it and see what happens.


glen.grant Tue, 11/04/2008 - 04:23
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I doubt spanning tree has any bearing on this . You have an ip path to all the devices in that you can ping them . Verify you don't have something like dup addresses . Try an snmpwalk against all 3 and see if they all respond . If so then its a net mgt. software glitch somewhere.

superdude5000 Tue, 11/11/2008 - 04:43
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I can verify SNMP is ok on all three routers, as in the network management console i see either one or the other, so have seen both of them monitored properly at different times. No dup addresses and a different NMS software is doing the same thing.

I can only think its STP doing it, maybe its blocking the link from the core bridge instead of the link between the two other routers? Is there any way i can confirm this?


Giuseppe Larosa Tue, 11/11/2008 - 06:06
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Hello Jamie,

STP manages a topology with redundant links by blocking redundant links.

However, this doesn't isolate any device.

if from the NMS you can ping all the devices and you can put an SNMP get over a MIB on any of them there is no network issue.

Verify if your NMS is not running in demo mode as suggested by Francisco may be because it didn't find the license file or it is expired.

just one thought: have you associated to the device an HSRP VIP address or something like that in the NMS map ?

if so this could explain what you see

For spanning-tree use

show spanning-tree summary

show spanning-tree vlan vlan#

verify that for a given vlan all switches agree on root bridge ID.

This should be enough to verfiy STP is working well

Hope to help



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