Replace 3550's with 2811 & HWIC's

[danletkeman]

I'm wondering if anyone can see any potential problems with changing out my 3550's with 2811 routers & HWIC cards?

There are three locations. All have a single 3550EMI doing OSPF between each other. They are all connected together to form a loop. Each location has up to 9 other sites connected to it with 2950's trunking back to the three 3550's. Each of these locations has multiple vlans, voice, video and data. Each of the 3550's are doing inter-vlan routing, policy based routing, and trunking.

Would a 2811 be the right choice for something like this?

Thanks,

Dan.

[mihanlin]

Hi Dan,

It depends on the size of the sites and what you are looking for.

The Etherswitch modules do line-rate switching at layer2 between the switchports in the same Vlan, but route layer3 in software - which will give you a slight performance hit in comparison to your current multilayer switches.

You can also only have a maximum of 15 vlans on the HWICs which may or may not impact on your needs.

You also cannot assign ip addresses directly to the switchports, and instead will have to use SVI's. This isn't normally a problem nowdays as most people implement SVI's instead anyway.

Hope this helps,

Michael.

[danletkeman]

Michael,

Yes it helps, but it also creates some more questions.

What kind of performance decrease could I see with moving from a multilayer switch vs a integrated service router?

I did see that the HWIC's only support 15 vlans on them, but if those HWIC's were all just doing trunking to another switch would the vlan limitation matter? Esentially the vlan limitation would only be what the router is capable of.

SVI's are currently what I'm using on the 3550 anyway's.

Also, I know that there are features that a router has that I am in need of that the switches do not have. Would a router on a stick be a better option instead of replacing the switches?

Thanks again,

Dan.

[royalblues]

Hi Dan,

The router on a stick architecture for vlans is generally a differed architecture.

it seems like you are going back in time. A layer 3 switch typically views its routing engine as a connected router on a stick.

what i dont understnad is why you want to replace the 3550 with the ISRs. You could either upgrade the same with a 3750 or a 4948 running Ip services image.

HTH

Narayan

[danletkeman]

So upgrading to a 3750 running the Ip services image would give me the same options as an ISR?

For example, A few weeks ago I really needed to do a "PBR Recursive Next Hop" policy route and the 3550's do not support that. I know that the ISR's do. Is that something a 3750 would support?

The 3750 seems to be a little out of my price range, would the 3560's do the job as well?

Is there a place I can go to see the differences between the switches, and maybe see the features available?

Thanks,

Dan.

[mihanlin]

Hi Dan,

Performance with a HWIC will be zero if you are just doing layer2.

The throughput from HWIC to/from CPU is limited to 200mbps bidiectional, all SVIs share this bandwidth.

In response to your second question: trunking requires you set up each VLAN in the database. Therefore, you are still limited to 15 vlans on the HWIC even if they are trunking through.

Lastly, router on a stick configuration is still limited by the physical speed of the cable you are connecting to it, along with the routing throughput of the router you are using on the end of the 'stick'.

As far as an overall indication of performance decrease, the setup will depend largely on what data you are sending where, and how much. Are you doing a lot of inter-vlan routing?

Your last option would be to keep the 3550s and make them do inter-vlan routing. Then, have a static default route to the router which can handle the policy-based routing functionality.

Michael.