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Best method to connect two Dell 2748 switches in same rack.

Posted on 2008-10-06
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Last Modified: 2011-10-19
HI,  I've got a network using one 2748 switch.  I'm running out of ports so I'm looking to see if I can buy another one and link it to the original 2748.  THey will be in the same rack with about 2 U space between them.

First, Is this possible?

Second, whats the best way?  Use one (or more) Gigabit cables?  Use transceivers?

Finally, how do you do it?  If there's configuration work required on the swtiches, I'd appreciate a dummies guide on how to set it up.  (I've already set the swich into Managed mode)

Many thanks
John
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Question by:jmsjms
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by:ngravatt
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first, yes.

2. You need to connect the two switches together with a cross over cable.  If there are gigabit ports available on the two switches, use them to connect the switch.

Now you will need to configure two trunk ports on the two 2748s where they are connected together.

I would configure an IP address on VLAN 1 of your new switch also.

Once you have the cross over cable connected, and an IP address configured, you should be able to ping the new switch from the old switch.
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by:Soulja
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You don't need a cross-over cable. A straigh-thru will work. Most modern switches will automatically detect this and adjust their ports.
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by:Pugglewuggle
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First off, the asker didn't say VLANs were even used.
Either way, the first way to start is to simply use a crossover cable (might not matter if your switch has MDI/MDIX crossover connection). Just run it from the fastest port on the switch to the fastest port on the other switch (usually the ports designated as "uplink" ports) and if you don't have VLANs this will work fine.
If you do have VLANs let me know and I'll advise you of the best way to do it. Please provide current VLAN config if you do have VLANs setup.
Cheers!
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by:Soulja
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First off, the asker didn't say VLANs were even used.

ngravatt mentions assigning an ip address to vlan 1 interface for management purposes over the network.



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by:Pugglewuggle
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Soulja, is ngravatt is not the asker. jmsjms is. We don't yet know if the asker is using VLANs. Sorry.
jmsjms, please let me know if you're using VLANs or not.
Cheers!
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by:jmsjms
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Thanks for your responses.  To confirm I do not run a VLAN.

I'm looking for a specific best method for the Dell 2748.  I know most switches (well un-managed ones anyway) can just be linked by daisy chanining ethernet cable, but I'm looking for a specific method for the 2748 as it can do trunking and/or use transeivers but I dont know how to use them and which it best to use.  

To clarify, just bunging a cable between them will work but it's going to limit cross-swtich traffic.  I want to use the capabilities of this switch to ensure that this doesnt become a bottle neck.

Cheers John
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by:ngravatt
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do you have gigabit ports on the switch.  Can you give the exact model number of the switch and i can check for you.

100 meg or 1 gig connection between two switches will usually not cause a bottle neck.

also, you can configure and etherchannel port between the two switches and combine 4 physical ports to be one virtual port and use that as the link between the two switches.

let me know and i will tell you how to configure it.  

ps guys, VLAN 1 is the default VLAN already on a switch.  It is already there.  You give it an IP address to manage the switch.  No, this is not the only way, but this is a way to configure a new switch.  
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by:Soulja
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On Dell switches they are call LAG's. The LAG will allow you to add several ports to make a virtual port, but the bandwitdth isn't accumulated. By this I mean if you have 4 100Meg uplinks bundled, that doesn't mean you have a 4Meg uplink. You still have 4 100 Meg uplinks. All  the lag will do is load balance traffic across the four links.

Also, note that if you are not running more than just the default vlan between the switches, then it is just a simple uplink, not a trunk. If you do decide to add additional vlans remember that the default VLAN1 on Dell switches is not routable.
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by:jmsjms
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Hi All, Im not using VLANS (apart from whatever the default setting is) and dont intend to do so.

The switch is a Dell 2748. (48 Gb sockets, 48 10/100/1000BASE-T auto-sensing Gigabit Ethernet switching ports
4 SFP fiber combo ports provide support for 1000BASE-SX and 1000BASE-LX transceivers
Auto-negotiation for speed, duplex mode and flow control
Auto-MDI/MDIX
Integrated LEDs for improved visual monitoring and analysis
Supports Virtual Cable Diagnostics by MarvellTM  and fiber transceiver diagnostics to provide advanced
troubleshooting capabilities for your cable infrastructure  

The questions remain.

a) whats the best method to put two together? Transceivers/group Gb sockets So there is no bottle neck.  (All clients have Gb Nics, the server has two).

b) how do you do it?  If there's configuration work required on the swtiches, I'd appreciate a dummies guide on how to set it up.  (I've already set the swich into Managed mode)d
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by:Soulja
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A) If the switches are not going to an area of high interference and are not very far from each other, go with copper uplinks. Just use two of your availabe gigibit ports and save the money on buying transcievers for fiber or copper.

B) Just connect the switches together with a cat 5e or 6 cable and they are talking.
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by:Soulja
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No addition vlans, no additional configs needed. You are basically using these switches like unmanaged switches.
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by:ngravatt
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in order to manage the switch remotely, you will need to assign an IP address to it.

but like soulja said, simply connect the two switches together with a regular network cable.  

plug a PC into each of the switches and make sure you can ping them.  If so, you are done, if not let us know and we can troubleshoot.
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by:jmsjms
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Thanks.

As mentioned above, I've got a server with two Gb cards, each client has a Gb network card.

Surely if I just use one cable  and I put the server on one switch then there's going to be a bottle neck for any pcs on the second cascaded switch?

In my limited understanding, I THINK you have to do some config to run more than one connection between switches?

Sorry I havnt got the second switch yet, I'm just getting prepared!

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by:Soulja
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console# configure
console(config-if)# interface range port-channel all
console(config-if)# shutdown
console(config-if)# interface range ethernet g(1-4)
console(config-if)# channel-group 1 mode auto (add those ports to LAG 1 (of 8), and use the LACP protocol to configure the LAG)
console(config-if)# int range port-channel 1
console(config-if)# no spanning-tree disable
console(config-if)# flowcontrol on
repeat the above on the partner switch and it's LAG ports
console(config-if)# no shutdown

Please ensure that you enable spanning tree on both switches before connecting multiple uplinks for the LAG or you will surely get switching loops.




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by:jmsjms
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Ah, this looks like the stuff.

THis for two cables ?

console(config-if)# interface range ethernet g(1-4)     <-- this bit - is it an option for me or do I type this literally in?

Where did you get this?  I havnt seen any dell manual showing COmmand line commands.

Thanks J
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by:Soulja
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That command is selecting a range gig interfaces, so that you can apply the following commandS to them at the same time. The range can be whatever interfaces you want for the LAG as long as they have the same bandwidth. You don't necessarily have to select a range. You can configure the ports individually, especially if the ports aren't consecutive.

This should help:

http://www.dell.com/downloads/global/products/pwcnt/en/pwcnt_5316m_cisco_interop.pdf


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by:Pugglewuggle
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Sorry jmsjms... Soulja was giving you Cisco commands to setup an EtherChannel... don't know what he was thinking.
If you don't need port aggregation (linking multiple ports into one link that gives you like 2Gbps) then the easiest thing to do is just connect the cable between the two switches and it will work.
This will be fine for almost any setup. Adding port aggregation just complicates things unnecessarily if it's not a requirement of the setup.
I don't know why others feel the need to complicate this so much. All you do is "plug one into the other with the fastest ports you can." That's it. No magic, no commands, no trouble. It just works.
Give it a shot and you'll see what I mean.
Cheers!
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by:Soulja
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Haha,

Puggle are you serious? If you haven't been in a Powerconnect lately, you would know that the CLI is almost identical to Cisco's except for proprietary commands. Also, it is obvious that jmsjms wants to create a LAG group so I provide the information.

jmsjms,

Please refer to that link I provided. It will help you out.
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by:Pugglewuggle
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As is nortel's and others. :) I do know. :) They all copied IOS.
I do know how it works BTW. I was simply saying that for a simple setup where less than 125MB/s of traffic goes across an interface then this is not necessary. I have seen almost no GigE setups (even with an etherchannel) where a large percentage of ONE GigE port was used up.
My point being - if you don't need it then don't complicate it! If you don't need 125 Megabytes/second of transfer (which you almost never do except in a heavily loaded datacenter) then don't set this up because it complicates things!
Cheers!
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by:Soulja
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Puddlewuggle,

I agree that the simpler the installation the better, and that a LAG is not necessary.  I stated that in an earlier post to just hook the switches up be done, but the author seemed to want information regarding port channels, so I provided the info. It's up to him in the end on what he wants to do.
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by:Pugglewuggle
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Fair enough. :) I said the same in my first post. Just connect 'em and they'll work!
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by:jmsjms
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Hi GUys, Many thanks for this informed discussion.  

I would like nothing better than to just plug in a Gb cable betweeen the ports however as mentioned above I'm concerned about a bottle neck.  Also, if theres even a little degredation in performance I'll have a whole load of users wingeing at me.  You know how it goes... :-)

Are you both telling me that even with one server with two Gb ports pkuggged into one Switch and the majority of the remainding ports filled up with Gb network clients, there will be no bottle neck between the switches?

Soulja - I've had a look at the document.  Very interesting.  I' tried telneting into the switch however and got no response.  I cant see any process for activating the CLI on the web interface.  However I found the page below.  Is all I need to do to make a couple of points in the same LAG group?



switch.gif
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Pugglewuggle earned 300 total points
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Hi jmsjms,
First off, that's exactly what I'm telling you. If there is not more than 125 MB/s (1Gbps) of traffic going back through the switch then there is no need for a LAG. There will be no decrease in performance and all will be well. If there is more than 125 Megabytes of traffic to and from all machines combined then you will need to create a LAG.
The thing about gigabit ethernet is that it is so fast the link is rarely filled up even 10%, and almost NEVER 100 (Even with heavily loaded servers you might see a spike at 20-30% occaisionally). Regular desktops just cannot fill up a link that fast - even a whole bunch of them at once. If you think about it, a 1GB link is so fast it could fill up an 80GB hard drive in just over 10 minutes. You don't have that kind of traffic going on, do you? If not, you probably won't need a LAG (although it doesn't hurt).
The fact is that you can run literally hundreds of computers off a single Gig port, under normal circumstances, as long as their just using regular business applications and not all streaming video.
Second, regarding the LAG setup, that is correct - just setup the appropriate ports in the same LAG group and do the same on the other switch and just connect the two.
Cheers! Let me know if you have any questions!
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by:jmsjms
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Solja

Agreed?

Cheers
John
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by:Pugglewuggle
Pugglewuggle earned 300 total points
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I guess soulja out for the weekend, but yes, those are they key considerations in determining if you need LAG, and that is the way to setup aggregation between switches.
Cheers! Let me know if you have any questions!
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by:jmsjms
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Thanks to all.
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