Load-Balancing traffic within a single vlan

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Apr 2nd, 2010
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Hi All,


I have a access network with 8 2960 switches and 2 3560 switches as their aggregation switches. I have dual links from each of the 2960 switches connecting to each of the 3560 switches. The 3560 switches are only aggregating the vlans at layer-2.I know pvst load-balancing is possible with multiple vlans. In my scenario is it possible to have load-balancing of taffic of the same vlan over different trunks.


Any help on the same would be appreciated.


Regards


Sushil

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Lei Tian Fri, 04/02/2010 - 15:35
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Hi Sushil,


Depends on your topology, if you have sperate vlan for each access switch, then maybe you can put the spt root on the access layer switch to have forwarding on both uplinks.


If your spt root is on one of the 3560s, then spanning tree will block one uplink, you cannot have both uplinks up/up.


HTH,

Lei Tian

Reza Sharifi Fri, 04/02/2010 - 15:47
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Hello Sushil,

In addition to Lei's comment, if you need more bandwidth and load balancing just create an etherchannel.


HTH

Reza

sushilmenon Fri, 04/02/2010 - 15:56
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Hi ,


Thanks for all your response.


I have 8 2960 access switches and 2 3560 switches. All the access switches are in the same floor and same vlan. there is only a single vlan in all the access switches.


The 3560 switches are only terminating the fibre uplinks from the access switches. the 3560 switches are further connected to 6509 switches on which the vlan svi's are created.


All the 2960 switches are having dual uplinks with each uplink connecting to each of the 3560 switch.


Now my query is that is it possible to have 4 of the 2960 switches use 1st 3560 switch as their primary path for reaching the Core and use the 2nd 3560 as backup path incase of failure of the 1st 3560 switch. and vice versa for the remaining access switches.


Is this configuration possible.


Regards


Sushil

Reza Sharifi Fri, 04/02/2010 - 16:35
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Hello Sushil,


On a given VLAN, you can only have one path forwarding and that is the one toward the root bridge.  So let say that 3560-A is your root and 3560-B is the backup root. In this case the primary (forwarding) connection is always toward the root (3560-A) and the backup connection (blocking) is toward the 3560-B.   


HTH

Reza

Lei Tian Fri, 04/02/2010 - 18:51
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Hi Sushil,


So you have 8 2960, we say 2960 1-8, and 2  3560, we say 3560 a and b. We want 2960 1-4 use uplink to '3560 a' as  primary path, and 2960 5-8 use uplink to '3560 b' as primary path,  correct? Assume 3560 a is the root bridge.


For that case, on 2960 5-8 you can change the spanning  cost on the uplink to 3560 a to a high cost, so the root port will be  the uplink to 3560 b. Then 2960 5-8 use uplink to 3560 b as primary path, and 2960 1-4 use uplink to 3560 a as primary path.


HTH,

Lei Tian

Ganesh Hariharan Fri, 04/02/2010 - 23:32
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Hi All,


I have a access network with 8 2960 switches and 2 3560 switches as their aggregation switches. I have dual links from each of the 2960 switches connecting to each of the 3560 switches. The 3560 switches are only aggregating the vlans at layer-2.I know pvst load-balancing is possible with multiple vlans. In my scenario is it possible to have load-balancing of taffic of the same vlan over different trunks.


Any help on the same would be appreciated.


Regards


Sushil


Hi Sushil,


As suggested by others just check out the below links hope that helps !!


http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800ae96a.shtml


http://www.cyberdogtech.com/school/cisco/switching/lab10/


Ganesh.H

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