Redundant Gig port on Separate Switch-2 nic card bonded

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Aug 7th, 2008
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My unix team has a servers with 2 different

nic cards on one box. Both are Active Active..both share the same MAC Address and IP. They would like to plug these two cards

into two different physical switches for redudancy.. Is this even possible?

We have switches that are stacked and this doesnt not seem to be an issue.

However, we are now connecting to switches that wont be stacked.

Is this possible?

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Marwan ALshawi Thu, 08/07/2008 - 19:28
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it will be good if u use the VSS module with cisco CAT6500

if u put them in the same switch will problems but two deffrent switches should work

especially if the comunication between swtiches is L3

nygenxny123 Fri, 08/08/2008 - 08:33
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I dont think the VSS is an option..any other


nygenxny123 Sat, 08/09/2008 - 07:50
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however the unix box with dual nics shares one mac and one ip.

Joseph W. Doherty Sat, 08/09/2008 - 09:26
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Yup, understood that's what the configuration is now, but likely such will require a connecton to the same physical or virtual device. Dual NICs should be able to be configured as different IPs and different MACs.

Giuseppe Larosa Sat, 08/09/2008 - 11:27
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Hello Richard,

it depends on the strategy of use of the NIcs.

if only one is used it is fine and doesn't provide problems to the switches.

If they want to use both at the same time or also to use one to send traffic and the other one to receive traffic (as sometimes they do) are problems.

The switches could start to complain of too much moves of the MAC address or of duplicated CAM entry.

Switches learn MAC addresses from traffic so frames would be provided to the TX only interface.

Two options for using both NICs at the same time:

-etherchannel with single switch using LACP;

- using different ip addresses and MAC addrs as already suggested

Hope to help



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