connect two 2960s to each other and to a 3750?

[jessica jestol]

I'm not sure of the best way to do this. I have one 3750 and two WS-C2960-48TC-L. Not 2960-S so no flexstack module. I was originally supposed to be getting 4 fiber runs from the 3750 to the 2960s. Two to each switch. I was going to create an aggregate link (ether/port-channel) and maintain a 2gb connection between the two 2960s and the 3750. Now, I've been informed that I'm only going to get two. What would be the best way to set this up. I was thinking as far as physical connections go, 1 fiber connection between each 2960 and the 3750 and then one fiber connection between the two 2960s. Would that work? And if so, what would be the best way to configure it to prevent looping?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Yes it would work.  You normally break the loop by using a STP.

When using a STP, you decide/design which link or links should block.

BTW, the SPF ports on the 3750 have dedicated RAM.  So, ideally, they should be used for your busier ports.

The 2960s share their RAM across all their ports, so depending on physical topology, you might interconnect them on non-SFP ports.

[jessica jestol]

Thanks for the answer. I was going to setup the two connections between the 2960s g0/2 and the 3750 as trunks. I'm not sure how I should configure g0/1 on the two 2960s. I was planning on connecting g0/1 to g0/1. If i set it up as a trunk, I shouldn't use spanning tree, correct?

[Jon Marshall]

Yes, you definitely need STP if you are going to connect like that.

But you should run STP anyway.

Make the 3750 switch the STP root for all vlans so the link between the two 2960s will be blocked at one end.

And run RSTP on all switches.

Jon

[jessica jestol]

Thanks! So I dropped spanning-tree portfast default and spanning-tree portfast bpduguard default on all the switches though to be honest, there's only 8 ports on the 3750 (out of 24) that are access ports. The rest are all aggregated fiber links.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Sorry, no, the link between all 3 switches well help with bandwidth, as one of them needs to be blocked.

However, if you're using IPTV, none of your video streams can be multicast?

[jessica jestol]

All video streams are multicast. But there are 70 different possible streams. If there is a different stream on all 48 interfaces, that's over a gig and will saturate the single fiber connection, correct?

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Well sure, if your aggregate bandwidth is more than a gig, you're going to saturate your link.  But, is it really likely that all 48 ports will be pulling concurrent, but different streams, at the same time?

[jessica jestol]

It hasn't happened yet that I know of but... my clients are all hospitals. We can't afford to take the chance. If a patient complains they're getting pixelation or freezing while watching TV... it looks bad on the hospital and us (violates contracts and SLAs, costs us money, etc. etc.) so... we go with better safe than sorry. That's why I was trying to jury rig some extra bandwidth out of those two 2960s since they only gave me two 1 gig fiber links. They had originally promised me four. 2 gigs for each access switch.

[jessica jestol]

Ignore this. I hadn't setup trunking on the ports I was using...

hmmmm, bpduguard shut the port down... Suggestions?

I added this:

3750
spanning-tree vlan 1 root primary

all switches
spanning-tree mode rapid-pvst
spanning-tree portfast default
spanning-tree portfast bpduguard default

04:39:30: %SPANTREE-2-BLOCK_BPDUGUARD: Received BPDU on port GigabitEthernet0/1 with BPDU Guard enabled. Disabling port.
04:39:30: %PM-4-ERR_DISABLE: bpduguard error detected on Gi0/1, putting Gi0/1 in err-disable state
04:39:31: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to down
04:39:32: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to down

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

If port is defined as a trunk, the default BPDUGuard (or Portfast) shouldn't be active, I believe.  You can override the global default, on any interface too.

[jessica jestol]

Ok so, it all seems to be connected fine now. I have one last question. Quick back story: We're running IPTV over these guys. Each video stream is 15-25MB. If all 48 ports are being used by a PC getting a video stream, it's more than 1gb. That's why we generally have two 1gb connections to the 2960. So, if I connect both these 2960s through g0/2 to the 3750 where the IPTV server is, and then connect both 2960s together, will that help? If there was a way to stack them I would do that but, these don't support the flexstack module.