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New Member

SVI vs Sub-interface on a Cat6509

Hi

We are looking for a solution that to use Sub-interface on a routed port on 6509, instead of using a SVI on it.

Are there any different when using Sub-interface?

Thanks,

3 REPLIES
Cisco Employee

SVI vs Sub-interface on a Cat6509

Hello,

Benifit of SVI is that it can provide L3 services for a group of Layer 2 ports within VLAN. Imagine you have 30 ports which are L2 (e.g. access) in VLAN 100 - to help those to route traffic to other VLANs - you create SVI100 and that is routing traffic to other SVIs or L3 ports just on this switch itself. Without SVI you will need additional router connected to this switch via trunk (so called router-on-a-stick) and sub-interfaces on it to do routing between VLANs.

So role of SVI is to do routing between VLANS on the switch itself. Role of sub-interface (if we talke about dot1q sub-interface and not about frame-relay for example) is to provide routing between VLANs for other devices and not locally.

Hope this helps,

P.S. If you can specify what you want to achiev and why you don't want to use SVI - possibly you canget more detailed answer

Nik

New Member

SVI vs Sub-interface on a Cat6509

the reason we are looking for the sub-interface is to against spanning tree problem within our network.

The scenario is about: there are two gateway 6509 (redundant), and two core switches (redundant). The connection between Gateway 6509 and Core are having a few vlans. But as the Core switches also connect so many other switches, we don't want the spanning tree extend to the gateway 6509. So now thinking to change the gateway 6509 to be sub-interface, and the core switches side are still trunk port.

But the biggest concern is if this change from SVI to sub-interface will have performance different or any others.

Thanks,

Cisco Employee

SVI vs Sub-interface on a Cat6509

Hello,

That should work fine. The reason to have SVI is to do routing between switchports (l2) within different VLAN on same switch. If you don't have any L2 ports on GW switch then you can do L3 sub-interfaces to the core. Just keep in mind - if later you will configure some L2 port (trunk or access) on your GW - you will need SVI for routing on GW for those ports.

Nik

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