Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Gigabit Interface Subinterfaces

When is there a performance hit when you subinterface a gigabit ethernet port?

We have a remote site with approxy 100-150 nodes. There is no layer 3 switch currently with which to implement VLANs. How bad of an idea is it to subinterface the router's inside interface to trunk down to the switch? There is a large amount of traffic traversing this router. While some traffic stays local for file storage and a few apps, a lot goes back to the hub site then out to the Internet. I was worried that the "hairpinning" might cause a performance hit. Currently there is no UC, but in the future there may be.

Thanks.

  • WAN Routing and Switching
Everyone's tags (2)
1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

Re: Gigabit Interface Subinterfaces

b.gamble wrote:

Thanks for the responses. Do either of you guys have any documentation to support?

I missed the 100-150 users but Paolo makes a very valid point. The 2821 supports 87Mb CEF throughput so if you have a large amount of traffic traversing the router then it will not be the subinterfaces so much as the actual capability of the router to forward packets.

As Paolo says, you would be much better off with a L3 switch such as the 3560/3750 which has much greater throughput and use the 2821 for WAN connectivity only.

Jon

9 REPLIES
Silver

Re: Gigabit Interface Subinterfaces

what is the router type and switch type?

New Member

Re: Gigabit Interface Subinterfaces

Router is currently a 2821. It might be a 3945 in the future. How much does processor speed and platform come into play when subinterfacing?

The switch in use is a 2960.

Hall of Fame Super Gold

Re: Gigabit Interface Subinterfaces

With 100-150 users, you must use a layer 3 switch for inter-vlan routing.

Hall of Fame Super Blue

Re: Gigabit Interface Subinterfaces

p.bevilacqua wrote:

With 100-150 users, you must use a layer 3 switch for inter-vlan routing.

Paolo

Recommending a switch and not a router - never thought i'd see the day

Jon

Hall of Fame Super Gold

Re: Gigabit Interface Subinterfaces

No, why ?

A layer 3 switch is a bad idea only when one expect it to do things it's not designed for.

Otherwise, a necessity.

Hall of Fame Super Blue

Re: Gigabit Interface Subinterfaces

p.bevilacqua wrote:

No, why ?

A layer 3 switch is a bad idea only when one expect it to do things it's not designed for.

Otherwise, a necessity.

Paolo

I was just joking, after some of our conversations in previous threads

I think you were spot on with the advice.

Jon

Hall of Fame Super Blue

Re: Gigabit Interface Subinterfaces

b.gamble wrote:

Router is currently a 2821. It might be a 3945 in the future. How much does processor speed and platform come into play when subinterfacing?

The switch in use is a 2960.

It is not so much processor speed rather the fact that you are limiting the amount of bandwidth per vlan because they are subinterfaced. If this is not an issue for you then it should not be a problem. The throughput of the router should be the same whether it is moving packets between subinterfaces or between 2 physical interfaces on the same router.

Jon

New Member

Re: Gigabit Interface Subinterfaces

Thanks for the responses. Do either of you guys have any documentation to support?

Hall of Fame Super Blue

Re: Gigabit Interface Subinterfaces

b.gamble wrote:

Thanks for the responses. Do either of you guys have any documentation to support?

I missed the 100-150 users but Paolo makes a very valid point. The 2821 supports 87Mb CEF throughput so if you have a large amount of traffic traversing the router then it will not be the subinterfaces so much as the actual capability of the router to forward packets.

As Paolo says, you would be much better off with a L3 switch such as the 3560/3750 which has much greater throughput and use the 2821 for WAN connectivity only.

Jon

1416
Views
5
Helpful
9
Replies
This widget could not be displayed.