3750<>2960 Cross stack concern

Unanswered Question
Jan 26th, 2012

Hello Guys ,

I am planning to impliment 2 cross stack etherchannel between 2 2960 <> 3 Stacked 3750

Problem is

Already there is a etherchannel 1 between 2 2960 .

I am afraid if I connect 3750 stack with these 2960 with etherchannel 2 and 3 there will be STP loop , your thought ?

Alos I Hvae put etherchannel configration on 3750 is below but dot1q i cant find in 2960 so is there diferent etherchannel config i should try

interface GigabitEthernet1/1/1

switchport trunk encapsulation dot1q

switchport mode trunk

channel-group 2 mode on

I have this problem too.
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Leo Laohoo Thu, 01/26/2012 - 13:21
dot1q i cant find in 2960

2960 supports dot1q so you don't need to enter the command "switchport encapsulation dot1q".

I just had a look at your VISIO and I all I can say is that you really don't need the etherchannel connecting both 2960 (etherchannel 1 in yellow).

The reason is because both already have an etherchannel to go from the 2960 to a stack of 3750.  If either one of the links fail, it'll still work (albiet with 1 link instead of 2).

If you intend to use the 2960 as a distro to the HP switches then I would be putting a dual link from the HP switches to the 2960 because this is where your single-point-of-failure is (link failure).

amtbhatnagar Thu, 01/26/2012 - 13:51

Thanks Leo for taking time n replying , doubts are below

1) Ok I will not put "switchport encapsulation dot1q" command on 2960 but on 3750 its allowed so shd i put it on 3750 r not?

2) Etherchannel 1 between 2960 is already existing and currently all servers are behind HP switches which are connected to 2960by access port for improving the architecture we are placing 3750 with 2 etherchannel proposed .

so all HP switches will go in future

3) now can you advice the 3 etherchannel are worth or not I can start by creating etherchannel 2 only then delete etherchannel 1 and create etherchnnel 3 .

any thoughts please

Reza Sharifi Thu, 01/26/2012 - 16:39

1) Ok I will not put "switchport encapsulation dot1q" command on 2960 but on 3750 its allowed so shd i put it on 3750 r not?

Yes

Which device is functioning as a router?

As Leo noted. if the HP switches are access switches, you need to uplink each one of them to both 2960s. If you are using the 2960s as layer-3 devices, then you need to configure HSRP or VRRP on them.

Instead of connecting the 3750 stack to one 2960 (as in the drawing) you need to uplink the stack to both 2960s using one Etherchannel

HTH

amtbhatnagar Sat, 01/28/2012 - 02:11

thanks Reza for your reply

regarding 2nd point u said to clarify Currently Al servers are behind HP swictches and HP switch is connected to Cisco 2960 on access port (thats not right but thats how its configured) and Cisco 2960 is connected to Firewall which is having gateway for the different VLANs

WIth 3750 i am trying to replace all HP switches and create a etherchnnel between 2960 and 3750 for better performace

Any thoughts would be great

Leo Laohoo Thu, 01/26/2012 - 22:52
1) Ok I will not put "switchport encapsulation dot1q" command on 2960 but on 3750 its allowed so shd i put it on 3750 r not?

Let me rephrase my first statement as it was made in haste.  The 2960 switchports will only support 802.1Q so the command "switchport encapsulation dot1q" is not required (or if you try to enter it, the appliance will cough up an error message).  The 3750, however, supports both 802.1q and ISL therefore you need to specify which one of the two flavours you want.

2) Etherchannel 1 between 2960 is already existing and currently all servers are behind HP switches which are connected to 2960by access port for improving the architecture we are placing 3750 with 2 etherchannel proposed .  so all HP switches will go in future

Let's put it this way, if your 2960 did NOT have etherchannel and were connecte with only one link each, then yes, this method sounds OK.  But with two links going to both 2960, I am still trying to understand the logic behind the third etherchannel.  In my opinion, you are just wasting two switchport (per switch) for this third etherchannel which does not make sense.

Leo Laohoo Fri, 01/27/2012 - 14:44

In addition, if you, say, had a 2960S then the third "link" would be your SmartStack.  Again, this would be redundancy at it's best but your HP switches with a single link is your single-point-of-failure.

amtbhatnagar Sat, 01/28/2012 - 02:18

i have got another option which i have attached in this reply lease share thoughts

In this i can get the current Cisco swicthes 2960  with  model number WS-C2960G-48TC-L  replaced with Stack of 2960 with model number WS-C2960S-48TS-L

In that case theer will be one etherchannel , is that a good design

Leo Laohoo Sat, 01/28/2012 - 03:05

Yes.  That's alot better.

Question:  Other than the HP switches and your two routers, what else are plugged in to the 2960S?

I mean, I would not dream of using the 2960S as a distro switch.  3750 as a distro switch is suitable.

amtbhatnagar Sat, 01/28/2012 - 16:33

hello Leo

Let me explain about network

1) it is a HUB location where there is no User in LAN only our MAIn servers are in this location which are accessed  by INternet or MPLS

2) Servers are currently behind HP switches which are connected to Cisco 2960 , the gateway for all servers is Firewall which is the main devie as its interface are uses for  mpls , internet , client network , and various vlans in HUb location in which all servers are located .

3) So i Thought to keep 2960 in same place so that all internet links can be connected on it and only servers should be connected on 3750.

I hope i am able to explain the architecture

You still feel 2960 and 3750are planned wrongly .

any thoughts are welcome

Leo Laohoo Sat, 01/28/2012 - 16:46

Well, let me put it this way, the 2960/2960G/2960S weren't designed as a distribution switch nor was it planned to service servers or in a data centre.  The only time I'd put a 2960 in a data centre is when the ports are going to be used for iLO/DRAK ports.

I just don't know where to start to explain what are the functional differences between a 3750X against a 2960S in a data centre space.  For a start, the 3750X stacking has a 32 Gbps (full duplex) compared to the 2960S of 10 Gbps (full duplex).  You can stack up to four 2960S but you can stack up to nine 3750 together.

The 3750X has dual power supply and can support stack power while the 2960S (because it wasn't designed for data centre) only has a single power supply and that's about it.

Modern data centre design has the Nexus family of switches as Top of Rack (ToR), End of Rack (EoR), distribution and core.

But the choice of either the Nexus switches or the 3750X is based on the size of your network.

amtbhatnagar Sat, 01/28/2012 - 17:03

Thanks For shairing valuable information .

I also have option of removing 2960from architecture completely .

In that case there will be Only 3750stack no  2960 and no HP swicthes .

In this case  I will be having various vlans on 3750 exampls servers vlan , internet vlan , mpls vlan , client vlan but there GW will continue to be firewall as it is now.

One question here how do you advice on this architecture I was worried from secuirty Point as Internet and server traffic will be on one switch even in different vlan .

Any thoughts please

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Posted January 26, 2012 at 6:27 AM
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