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If I configure a second interface on the router to connect to the same network as the other, will it cause spanning-tree to reconverge when I plug it into the switch?

E.g. existing interface is 10.1.1.1/24, and I need to configure and add 10.1.1.5/24. I don't want to wait until after-hours to avoid the network blip, but I will have to if STP is going to recalculate and reconverge.

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(I need to make some changes for the VoIP service-module which includes giving the router another IP on the same subnet. Other methods of configuring it, e.g. on a loopback adapter or in a new subnet have made it difficult to route.) –  ewall Aug 27 '09 at 15:35

4 Answers 4

up vote 2 down vote accepted

It all depends if you've configured your two interfaces to bridge and to enable STP. If it is not, then it won't make your STP re-converge, as your interfaces will no broadcast STP announcements. Adding an additional IP address will not make any difference as it's a different layer.

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Ah, yes... that makes sense now. To the switch, it just looks like I plugged in another device. And this router is not doing any switching nor participating in STP, of course. –  ewall Aug 27 '09 at 17:50

A router does not participate in STP. A "layer 3 switch" can though. But unless you're adding physical ports or adding/removing vlans STP won't even notice.

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i don't think it will, unless your router is also your switch, STP to my knowledge is Layer 2, ip is layer 3

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If the interfaces have different IP's there there shouldn't be a problem. That being said I still wouldn't do this during business hours.

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Good point... but the time crunch may make that decision for me. –  ewall Aug 27 '09 at 17:51

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