Cisco 2621XM ios 12.3 subinterfaces

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Aug 2nd, 2010
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Hello all,

Two quick question.

1. Can i have 6 subinterfaces on my 2621 router??

2. If so, will there be any degradation in my traffic? as the main physical 100mbps interface is being shared with the 6 subinterfaces.

Reason why am asking this is that i have 6 VLAN's and i want to do the intervlan routing on the router. We are not in a position to buy L3 Switches.


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Nagaraja Thanthry Mon, 08/02/2010 - 22:35
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You can certainly have 6 sub-interfaces on the interface. The number of

sub-interfaces is limited by the amount of memory you have and the amount of

memory the system can allocate to the virtual interfaces. The performance

impact depends upon the amount of traffic you are sending through the

router. As long as it is below the amount of traffic 2600 router can handle,

there should not be an issue.

Hope this helps.



terrencepayet Mon, 08/02/2010 - 23:02
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Hello Nagaraja,

Thanks for your prompt reply.

Can you tell me if the total amount of memory (please find attached) will suffice for the intervlan?



Nagaraja Thanthry Tue, 08/03/2010 - 08:47
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You should not have any issues with creating sub-interfaces on the router. Only thing you need to make sure is that you are not pumping traffic to the interface that is beyond its capacity i.e. the cumulative traffic should not exceed about 80 Mbps. Here is a good document on the number of subinterfaces supported on different platforms:

Hope this helps.



mbroberson1 Tue, 08/03/2010 - 19:29
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Hi Terrence,

NT is correct. We are using 2621XM's (64 memory 128 flash) doing router-on-a-stick with 10 or 12 vlans/sub intf's without any issues. If your location(s) are only T-1 (1.5mb) over the wan how could it hurt...:-)?



terrencepayet Tue, 08/03/2010 - 22:49
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Thanks for the info.

I have configure Intervlan on the router but the traffic peaks at 100mbps therefore losing connection to the router.

I have also configure CEF on the main physical interface with no luck.

Please find attached the sh proc cpu log.

As you can see the CPU peaks at 100% which is being handle by interrupt.

I don't know if the problem is with the memory or the CPU.




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