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Community Member

3750 stacking

Greetings,

I have little prior experience dealing with stacking 3750s and was looking for a little help.

We have 18 fiber pairs collapsed from the IDFs at the distribution layer and I'm looking for the most cost effective way to handle this. I figured I would stack 2- 3750G-12S to handle the fiber and then run a 2 gig channel between the 3750 stack and the core switch which is a 3750G-24-TS. Is this feasible and could I stack all 3 (Distribution switches and core) together and avoid the 2 extra SFP modules and fiber patch cables between the distribution and core?

Thanks in advance..

Regards,

1 ACCEPTED SOLUTION

Accepted Solutions
Super Bronze

Re: 3750 stacking

Torbjorn proposes an interesting variation, using just a stack of copper 3750Gs and their SFP ports in lieu of any 3750G-12S models. However, to cover loss of any one 3750 I believe you would need a stack of 6, since otherwise a stack of 5 with a failed unit would leave you only 16 SFP ports and your original post did mention you have 18 fiber pairs.

Torbjorn also describes otherwise needing 3 3750G-12S models and 2 3750G-24TS-1U models. To support your 18 fiber ports, a stack of just 2 of each model (or 3750G-24TS in lieu of the 3750G-24TS-1U) should suffice. Failure of a 3750G-12S would still provide 20 SFP ports (12 + 4 + 4).

[edit]

PS:

Rereading Torbjorn's post, he does mention having a spare 3750G-24TS-1U, for lab usage and on-hand spare, which provides the extra SFP ports you'll need. (My apologies to Torbjorn for missing this.)

[edit2]

Robert, since using 3750s is new to you, if you stack the distribution and core, I want to recap your options for supporting 24 copper and 18 fiber ports.

Without extra ports to cover loss of a 3750, you can stack:

2 3750G-12S and 1 3750G-24TS(or -U)

or

1 3750G-12S and 2 3750G-24TS(or -U)

or

5 3750G-24TS(or -U)

Extra ports to cover loss of any one 3750 are provided by:

2 3750G-12S and 2 3750G-24TS(or -U)

or

6 3750G-24TS(or -U)

For 3750 failure replacement avoiding the need to repatch and reconfigure ports:

3 3750G-12S and 2 3750G-24TS(or -U)

or

6 3750G-24TS(or -U)

Torbjorn's suggestion offers the major advantages of lost of a 3750 shouldn't take out as many active ports assuming you've distributed them across the stack. Second, if you want to swap the failed unit with the spare without reconfiguration (NB: there are some prerequisites to doing this), you only need 1 more 3750 vs. the mixed type of 3750s providing the same ability.

You didn't note what you were planning to use as your routing protocol, if any. When pricing units, take careful note of what feature set is being priced.

5 REPLIES
Super Bronze

Re: 3750 stacking

Should be able to stack just the two 3750G-12S or all three 3750s. Do note, the stack becomes one virtual device, so you've combined your distribtion and core. (If you do keep the distribution and core separate, also consider using a cross stack member channel.)

Advisable to insure all stack members start with exactly the same IOS image.

The 3750G-12S model has a SDM template unique to it, so if you do make a 3 device stack, insure the 3750G-12Ss are configured with a SDM template used by the 3750G-24-TS.

PS:

If you go for the combined stack, and add another 3750G-24-TS, you may have sufficient ports to cover the loss of any one 3750 (each 3750G-24-TS provides 4 SFP ports).

Community Member

Re: 3750 stacking

So I understand it will be easier to stack just the 2- 3750G-12S and run 2 fiber trunks between them and the core switch then configured using cross stack member channel? I have very large host bandwidth requirements. 700 devices with 10% running 20Mbps streams at one time. That means I need atleast 2gig available between core and distribution.

Super Bronze

Re: 3750 stacking

No, didn't mean to imply stacking just two fiber only 3750s with a channel to the other 3750 is "easier", just outlining other options and considerations. For instance, since you mentioned a two link channel, if you used a cross stack member channel, you avoid one 3750G-12S being a single point of failure. However, the stack also offers redundancy.

As to the aspect of bandwidth, the stack would provide more bandwidth than the two link channel.

Gold

Re: 3750 stacking

Short answer:

We do not know what uptime requirements you are to meet and so on. so therefor I would propose the following.

5 3750 1su = 20Gbic ports and 120 Gig copper.

Long Answer:

If you are to go with your original idea, what happens if one of the 3750-12S craps out ? so I figure you need to buy one of those extra anyway. Loosing 1/3 of the links for X ammount of hours/days is not good . and if you do not have a spare 3750-1su you might want to look at that too.

So in general to meet any uptime req you would have to buy 3 12s and 2 1Su.

lets just for arguments sake say that you already have the spare 1su.

I would look at 5 3750-1su in a single stack.

that would give me the following advantages.

1) same hardware/software all over

2) if one switch would break then you would max loose 2 links.

3) more ports over for other things

4) the stack would have 32Gb backplane speed.

If we now add the spare 37501su and you did not have it, then you would add the following advantages.

5) ability to bug check new software before installing it (trust me its needed)

6) cheaper smartnet contract.

7) you can use the spare 3750 to test and play with in a lab environment.

8) if link breaks you have an immidiate replacement no matter if it is core or dist device that fails.

The price is basically the same.

Do you have any HP switches or other brand to do a trade in with ?

HTH

Super Bronze

Re: 3750 stacking

Torbjorn proposes an interesting variation, using just a stack of copper 3750Gs and their SFP ports in lieu of any 3750G-12S models. However, to cover loss of any one 3750 I believe you would need a stack of 6, since otherwise a stack of 5 with a failed unit would leave you only 16 SFP ports and your original post did mention you have 18 fiber pairs.

Torbjorn also describes otherwise needing 3 3750G-12S models and 2 3750G-24TS-1U models. To support your 18 fiber ports, a stack of just 2 of each model (or 3750G-24TS in lieu of the 3750G-24TS-1U) should suffice. Failure of a 3750G-12S would still provide 20 SFP ports (12 + 4 + 4).

[edit]

PS:

Rereading Torbjorn's post, he does mention having a spare 3750G-24TS-1U, for lab usage and on-hand spare, which provides the extra SFP ports you'll need. (My apologies to Torbjorn for missing this.)

[edit2]

Robert, since using 3750s is new to you, if you stack the distribution and core, I want to recap your options for supporting 24 copper and 18 fiber ports.

Without extra ports to cover loss of a 3750, you can stack:

2 3750G-12S and 1 3750G-24TS(or -U)

or

1 3750G-12S and 2 3750G-24TS(or -U)

or

5 3750G-24TS(or -U)

Extra ports to cover loss of any one 3750 are provided by:

2 3750G-12S and 2 3750G-24TS(or -U)

or

6 3750G-24TS(or -U)

For 3750 failure replacement avoiding the need to repatch and reconfigure ports:

3 3750G-12S and 2 3750G-24TS(or -U)

or

6 3750G-24TS(or -U)

Torbjorn's suggestion offers the major advantages of lost of a 3750 shouldn't take out as many active ports assuming you've distributed them across the stack. Second, if you want to swap the failed unit with the spare without reconfiguration (NB: there are some prerequisites to doing this), you only need 1 more 3750 vs. the mixed type of 3750s providing the same ability.

You didn't note what you were planning to use as your routing protocol, if any. When pricing units, take careful note of what feature set is being priced.

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