What should I concern for configuring a Link Aggregation on DELL switches

Posted on 2011-10-02
Last Modified: 2012-05-12

I am planning to configure Link Aggregation on my 3 DELL Switches, 1 x 5448 and 2x 3448 switches.  What should I think ahead when doing configuration?

Please correct me from wrong, I believe that DELL 3448 come with 2 x 1 Gbps port and 5448 come with 48 x 1Gbps ports.  Therefore I am thinking to create a 2Gbps trunk for each 3448 switch.

Such as...

On DELL 5448 port 1 and port 2 link to 2 Gbps ports on DELL 3448 (A) to form LACP Group 1
On DELL 5448 port 3 and port 4 link to 2 Gbps ports on DELL 3448 (B) to form LACP Group 2

Except this, what should I consider, Spanning Tree issue?  In this scenario, would it create any spanning tree problem?

Do I need to VLAN in order to do such configuration?
Question by:KANEWONG
    LVL 57

    Expert Comment

    As long as 3448 (A) and 3448 (B) are not connected to each other you don't have to worry about spanning tree.

    As long as you have a single IP Subnet  you don't need VLAN's.

    The only other possible thing you may want to do is not use adjacent ports for the same LACP group.

    It has been awhile since I have seen the internal design published for switches.  But at one time switch ports were grouped together in groups of 4 or 8.  A group would share certain internal paths, say ports 1-4 (or 1-8) would share the same memory for buffers and the same ASIC as a controller chip.  Typically there was enough capacity for about 1/2 of the ports in the group to run at 100%.  But performance was the least of the issue.  The main issue was chip failure.  If the memory or controller chip for a group of ports failed, all the ports would fail.

    So in your setup if you had a share component for ports 1-8 (or even 1-4) fail, you loose your up-links for all switches.

    For this reason I typically separate up links to the same switch by at least 8 ports.  Now it could be that you don't have to worry about this anymore, but old habits are hard to stop.
    LVL 1

    Author Comment


    How can I figure out what internal path used in my DELL 3348 switch?

    Also, how to test the bandwidth to know the increased bandwidth?
    LVL 57

    Accepted Solution

    You would need to see if Dell provides information in the technical doc for the switch.  I looked and they do not seem to provide this information.

    The only way to test the increased bandwidth it is perform multiple large data transfers with a single link and then do the same test with multiple links.  

    You will need to do the test with multiple computers as the source and target.  Unless they have changed something, link aggregation does not help when there is only a single pair of computers involved in the transfer.  A single stream (normally based on source and target mac access)  will only go across one link in a group.

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