4900M Configuration

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Dec 16th, 2009
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We have 10 switches in the datacenter but only have 5 connections back to our 6509 core switches running as a VSS pair.  We purchased a couple of 4900M to bring 10G to the datacenter and provide dual uplink on every switch back to the core.  I will have dual 10G links on each 4900 back to the 6509 and plan on using a 1G link on each 4900 to each switch.  Right now the 6509 does all the VLAN routing. 


My question is in the best practice configuration of the 4900.  Do I configure this as just a layer 2 switch with every port set as a trunking port?  Or should I be moving any layer 3 routing to this switch? 


I'm thinking of using it just as a layer 2, but want to make sure I'm doing this right before putting in in production.


Thanks

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Jon Marshall Wed, 12/16/2009 - 15:06
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jeffreydorn wrote:


We have 10 switches in the datacenter but only have 5 connections back to our 6509 core switches running as a VSS pair.  We purchased a couple of 4900M to bring 10G to the datacenter and provide dual uplink on every switch back to the core.  I will have dual 10G links on each 4900 back to the 6509 and plan on using a 1G link on each 4900 to each switch.  Right now the 6509 does all the VLAN routing. 


My question is in the best practice configuration of the 4900.  Do I configure this as just a layer 2 switch with every port set as a trunking port?  Or should I be moving any layer 3 routing to this switch? 


I'm thinking of using it just as a layer 2, but want to make sure I'm doing this right before putting in in production.


Thanks


Jeffrey


There are quite a few discussions in the forum on this ie. L2 vs L3 access-layer. Different people have different views. I have implemented both routed access-layers and  L2  access-layers, the routed in a campus environment.


Personally i think routed works well in a campus environment but for a data centre i would still use L2. The reasons are primarily -


1) more flexibility in server placement ie. if you use routed access-layer then if you need to move a switch to another vlan then you may well need to physically move the server depending on your patching


2) just as importantly some services that you want to use in a data centre such as firewalling / load-balancing can be used in either routed or transparent mode. If you deploy a L3 routed access-layer you automatically rule out some deployment options with these services.


Obviously L3 negates the spanning-tree issue but if you are running VSS anyway that should not be an issue for you.


I would still look to deploy L2 in the data centre at the access-layer because it simply gives you more options.


Jon

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