Channels or trunks? and/or L2/L3 link btwn Access to Core?

Unanswered Question
Sep 30th, 2007

I have a 2 layer architecture so just a bunch of access switches, 2 redundant cores and no distribution switches. All ports are 1GB. I have 2 questions base on what I read on the SRND www.cisco.com/go/srnd

1. Is it recommend to use trunk or channel btwn access to core?

SRND seems to recommend trunks but given a recommend 20:1 ratio on the access layer, this would imply Layer 2 channels as I am using a /24 on each access switch while avoiding spanning the vlans across switches.

2. I am considering using a routed campus design, but SRND uses 1Gb in their examples. Can I use a Layer 3 channel instead?

Basically, SRND doesn't seem to recommend channels on the access layer and I am not sure why?

TIA

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Jon Marshall Sun, 09/30/2007 - 23:33

Hi

When you say channel i assume you mean etherchannel ?

1) Trunks and channels are not an either/or choice. You would use a channel when you need to aggregate the bandwidth of more than one port. So if you need an uplink of 2Gbps you can channel 2 x 1Gbps ports togther.

A trunk is for carrying multiple vlans. You can use a trunk on a single link or a channel. You would use a trunk when the switch has more than one vlan on it connecting to another switch.

2) Yes you can use an etherchannel for L3 instead of just one single connection. L2 and L3 etherchannels are just aggregations of more than one port. It all comes down to how much bandwidth you need from the access-layer.

HTH

Jon

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