[c-nsp] Vlan interface vs. sub-interface

Ziv Leyes zivl at gilat.net
Tue Apr 1 03:15:26 EDT 2008


I've made this a several times on small endpoint routers, the customer had a Switch with a few VLANs and then connected a trunk port to a 1841 or 2811 router to a FastEthernet port on the router.
Here's a brief example:

interface FastEthernet0/0
 description Connected to switch trunk port
end
!
interface FastEthernet0/0.10
description VLAN 10
encapsulation dot1q 10
end
!
interface FastEthernet0/0.100
description VLAN 100
encapsulation dot1q 100
end
!
And so on...
Hope this helps someone.
Ziv


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Dan Armstrong
Sent: Tuesday, April 01, 2008 5:06 AM
To: David Coulson
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Vlan interface vs. sub-interface

I've never seen a mixed L2/L3 platform that supported SVIs where you
could make subinterfaces and set vlan encapsulation.... ?





David Coulson wrote:
> One of the big advantages of sub-interfaces over VLAN interfaces is that
> if 'VLAN 100' on one port is a totally different network to 'VLAN 100'
> on another. Using a sub-interface you can configure them as unique L3
> interfaces. I've done this a lot with dot1q handoffs, and it works nicely.
>
> Is there a mechanism in place for QinQ mappings to a SVI? Never really
> dealt with that before, but now I'm curious.
>
> David
>
> Nate wrote:
>
>> I'm trying to put together a table of advantages (and disadvantages)
>> of a vlan interface (SVI) vs. a sub-interface of a physical port. So
>> far, I have the following.
>>
>> SVI
>> ----
>> Advantage:
>> -Ability to add redundant link to the L3 interface
>> -Better counter and statistics displayed through CLI
>>
>> Disadvantage:
>> -Need to be mindful of Spanning Tree issues on redundant links
>> -The number of SVI supported maybe limited dependent on platform?
>>
>>
>>
>> Physical port sub-interface
>> ---------------------------------
>> Advantage:
>> -Easier to configure and supported on more platforms?
>>
>>
>> Disadvantage:
>> -Inability to add L2 redundant links
>> -Statistics on CLI limited
>> -Bandwidth limited to physical port
>>
>>
>> Are there more significant advantages/disadvantages (e.g. buffer
>> limit, queue depth) that I'm missing?
>>
>> Thanks,
>> Nate
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>>
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