Router on a stick

1 - All 3550s are not L3 switches.
2 - A 4506 can be L3.
3 - You don't need a router at all on a switched LAN, only to route between subnets and VLANs.

Missed part of this

If you have 1 subnet per 3550 then you will need a routing device.

The 4506 is L3 capable if you have a big enough sup engine.  Otherwise, yes, you need a router.

All the 3550's I have here are Layer 3 capible.  I don't know that I want the 4506 doing all the routing, so I guess I will need to use the router on a stick.  I wanted to make sure I wasn't using an extra device I didn't need.  Any other ideas?

Create a star mesh using the 3550s and route there.

This will eat up 4 ports on each 3550.

This is the way I have configured router on a sitck in the past.  The Hosts default gateway was the IP of the 3550 switch, then there was an IP default gatway statement on the 3550 pointing the the respective IP address on the router.  Is this correct?  From the statement above,  the default gateway is supposed to the the router's address?  

If each 3550 is it's own subnet, the DGW address needs to be in the host subnet.

The way you have it is fine.

Using the 3550 as the host's gateway, then pointing the 3550 to the router via a default gateway will work, but it's redundant and adds an extra hop...

If you're using router on a stick, the switches should all be "dumb" layer 2 switches only.  Set up the subinterfaces on the router with an IP address from the host subnet, and point the hosts toward that.

But again, if it ain't broken...

All 3550s are in their own subnet , 2 of the 3550s are in the same subnet,but thats just because I needed to add an additional switch due to needing more ports for that particulatr network.  So I have one switch with a 192.168.1.10 address, and one with a 192.168.1.11 address and those two switches have a default gateway of 192.168.1.1 which is the router on a stick sub interface.  I guess I will leave it just the way it is.  In the past I have normally only used layer 2 switches with router on a stick, because I had layer 3 switches, I was curious if I even needed the router.  I guess there is no real benefit for changing it.

Exactly.

Actually, with those details, I would say your network is actually a decent candidate to ditch the router on a stick and do some Layer 3 routing.

How are your VLANs set up?  Is everything in the default VLAN on each switch?  Or have you done any customizing there?

I assume your 2621 is at the WAN or Internet router edge ?

Your diagram is perfectly set to have the 4500 be the router, you can still do unique subnets/VLANs for the 3550's. This is exactly how we handle a switch closest or small office.

Manage the 4500 as the L3 router for the LAN, use the 2621 as the edge.

The 3550s are all configured with their own VLAN.  
Switch 1- vlan 20
Switch 2 -vlan 30, and so on
Then my router look like this:

interface FastEthernet0/0.20
 encapsulation dot1Q 20
 ip address 10.0.16.1 255.255.240.0
 
interface FastEthernet0/0.30
 encapsulation dot1Q 30
 ip address 10.1.0.1 255.255.0.0

If you don't expect heavy traffic in inter-vlan talk - then you should stick with what you got.  If you do expect heavy traffic like backups from all vlan to talk to another vlan - then get off that router on a stick and enable L3Routing on that 4500.  You'll have more flexibility, reduce TCO on your network by reducing the amount of actual devices needed, consolidate configuration and management, and be more flexible when thinking about redundancy.  

You're assuming the 4500 has a L3 capable supervisor, which hasn't been clarified yet.

Crossroads,

You could move the 'ip address' commands to the 3550s.  Each 3550 would get a command like

interface VLAN xx (where xx is the vlan number in use)
ip address a.b.c.d w.x.y.z
no shutdown

You would then need to set up a routing protocol, so that each 3550 tells the other 3550s about the subnet it is "managing"

router eigrp 1
network a.b.c.d w.x.y.z   (careful here, the addresses used with the EIGRP command are the network address and the wildcard mask.  You can find the wildcard mask by taking 255.255.255.255 and subtracting the subnet mask.)

So in the end, if I were you, would I do this?  Only if I was seeing a performance problem or needed to get rid of the router for environmental reasons like I needed the space, it was broken, etc.

is EIGRP included with SMI or just EMI on the 3550's, my impression is that it is on EMI only, which he would have had to purchased intentionally.

Yes author needs to quickly verify that the 4500 does indeed have a L3 Sup. If it does that avoids all of the routing protocol and static routing complexity.

True, EIGRP is available only in EMI, though most off-the-shelf router packages I have seen ship with EMI as a base IOS.

If there isn't EIGRP support in the 3550's IOS, then RIP is probably acceptable, and RIP is included in SMI..

You can check if you have EIGRP support by doing 'router ?' from the config prompt and checking for EIGRP as a valid command.  Or 'show version' and look for EMI in your IOS filename.

The 4506 does not have layer 3 capibilites, so I will not be able to use it to replace the 2621 router that is currently the router on a stick.  My 3550's are capable of using eigrp.

I have been doing some testing, and it seems when backups are running it really slows down the performance of the network.  When I ping the router on a stick during backups, the pings are like 10000ms.  If I pause the backups the pings go back down to about 18ms.  Any suggestions on what to do to improve me network performance, without replacing the router on a stick?

I assume that you are doing a central back up (across multiple VLANs) and that all backup traffic needs to go through the router.

This would cause the problems you are talking about.

The solutions are

1 - decentralized backup (a back up in each VLAN).
2 - router with a faster interface (gig-E)
3 - the mesh set up I was talking about.
4 - or daisy chain the L3 switches and eliminate the router.

Clarification on #4

I was thinking that instead of doing a mesh, connect the 4 3550s in a bus config

SW1--SW2--SW3--SW4

with a trunk between them.

If they are L3 switches, then SW1 will know the route to SW4, via SW2... etc...

This is what is weird.  I am not doing a central backup, each subnet/network, has its own backup server so its not  going across other VLAN's, but as soon as I stop backups, the network performance is drastically better.  Maybe I need a faster interface card.