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Author Topic: SMLT and STP  (Read 2882 times)

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Offline sergey_ta

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SMLT and STP
« on: October 09, 2013, 12:08:22 PM »
Hello!

In our project we have a “bad” topology that make us use STP for one VLAN. For rest of the network we could use SMLT. But because of that VLAN we cannot imagine how to stay with SMLT and not to go to STP on all network.

The topology is: we have 2 core VSP9000 and some ERS8800/5500 at distribution lever. Every ERS connected to every VSP9000.  There is a “chain” of switches with cameras connected to them, that connect pairs of ERS between them (see diagram in attach). Because of this chain we have a loop.

Could you suggest some decisions to stay with SMLT and to provide resilience for chains of cameras? The problem is that SMLT don't support STP. I would be glad for any ideas!
« Last Edit: October 09, 2013, 12:10:29 PM by sergey_ta »


Offline Johan Witters

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Re: SMLT and STP
« Reply #1 on: October 09, 2013, 07:19:21 PM »
If spanning tree is correctly configured on the rest of the switches, the switches should be able to detect the loop and put 1 of the links in blocking.

Best would be to give 1 of your 5500's a lower priority to make it "root" in the STP part of the network, the other switches should be able to figure out which link to block, but if you like you can change the priority or cost on 1 particular port so the network will always keep the same link down.
Kind regards,

Johan Witters

Network Engineer
BKM NV

Offline sergey_ta

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Re: SMLT and STP
« Reply #2 on: October 10, 2013, 01:50:54 AM »
Johan, thank you for your answer!
Have you ever use STP with SMLT in real network? Could you describe it with more details?
When we try to make our topology in laboratory we have a loop, because we cannot enable STP on SMLT. So BDPU havenít gone over SMLT. So other switches donít understand that there was a loop.

Offline Johan Witters

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Re: SMLT and STP
« Reply #3 on: October 10, 2013, 06:23:37 AM »
Hello Sergey,

I've taken another look at the drawing now that I'm fully awake..

In your current design indeed you will have a loop that cannot be fixed by the STP protocol. Because the SMLT links don't run STP, the rest of the switches do not see them and do not take them into account.

I have a similar design running, but the main difference is that in my case the "loop" would be fully connected on 1 5500, not split over the 3 5500 switches.

Do you have a possibility to stack the 5500's making the SMLT to the core? If that is possible, make that stack "root" switch in the STP topology and the network should be able to cut the loop.
If not, you could try to cut your camera network into smaller segments, but that would create a single point of failure if a 5500 goes down.

Otherwise I think you have indeed reached the limits of the SMLT design
« Last Edit: October 10, 2013, 06:41:30 AM by Johan Witters »
Kind regards,

Johan Witters

Network Engineer
BKM NV

Offline sergey_ta

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Re: SMLT and STP
« Reply #4 on: October 10, 2013, 01:58:10 PM »
Johan, thank you very march for advices! It was my first post at this forum and Iím glad that it wasnít  ignored!
But, unfortunately, our ERS5500 situated in geographically separated points. And idea of desingers was to make resilience for chains of cameras. And it were only a part of network, really we have about 50 chains of cameras between 50 geographically separated ERS5500.