Solved

STP Question

Posted on 2015-02-04
5
83 Views
Last Modified: 2015-02-07
Hi
Spanning tree Root Bridge for a vlan can never be behind a routed device (Layer 3)
Is this correct
0
Comment
Question by:ciscosupp
5 Comments
 
LVL 50

Accepted Solution

by:
Don Johnston earned 300 total points
ID: 40589683
Not sure I understand what you're asking.

Spanning Tree BPDU's cannot pass through a router. So if you had two switches separated by a router, both switches would be a root bridge.
0
 

Author Comment

by:ciscosupp
ID: 40589698
That’s what I was looking for thanks.

But you can configure a router to be spanning tree Root Bridge for a vlan.
Is this correct
0
 
LVL 50

Expert Comment

by:Don Johnston
ID: 40589719
That's a tough one...  A "router" is a layer-3 device that doesn't run STP.  

However, some routers have switch modules that you can install. Those switch modules are able to run STP.  

Also, on some routers you can disable layer-3 on a per interface basis at which point the interface is now a layer-2 interface and does participate in STP.  

But then you're not really talking about a router at that point because it's basically a switch (at least the interfaces in question are).
0
 
LVL 9

Assisted Solution

by:nattygreg
nattygreg earned 50 total points
ID: 40589947
What you want is a switch 3550 is a good choice for that. No spanning tree behind a routed device.
0
 
LVL 28

Assisted Solution

by:mikebernhardt
mikebernhardt earned 150 total points
ID: 40590054
You can take a router and make it bridge between 2 (or more) layer 3 interfaces, which means it isn't routing between those 2 interfaces. In that case it passes BPDUs and can participate in STP, or even be the root bridge.

If you use Integrated Routing and Bridging (IRB) You can even assign an IP address to a bridge interface so that it can route IP over those bridged physical interfaces. Strange, but true. We used to do this in order to let a router route from a T1 to a LAN through 2 different Layer 2 switches on the same VLAN.

I'm not saying this is the best design, just that in answer to your question it can definitely be done.
0

Featured Post

Scale it in WD Gold

With up to ten times the workload capacity of desktop drives, WD Gold hard drives employ advanced technology to deliver among the best in reliability, capacity, power efficiency and performance.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Meet the world's only “Transparent Cloud™” from Superb Internet Corporation. Now, you can experience firsthand a cloud platform that consistently outperforms Amazon Web Services (AWS), IBM’s Softlayer, and Microsoft’s Azure when it comes to CPU and …
When it comes to security, there are always trade-offs between security and convenience/ease of administration. This article examines some of the main pros and cons of using key authentication vs password authentication for hosting an SFTP server.
Here's a very brief overview of the methods PRTG Network Monitor (https://www.paessler.com/prtg) offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're looking for how to monitor bandwidth using netflow or packet s…

863 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

26 Experts available now in Live!

Get 1:1 Help Now