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Community Member

Where to put the default gateway for best performance

I have a Cat 4507R running redundant Sup IV modules and a 2851 router. I have 10 VLANS. To achieve the best performance,

where should I place my gateways? should I turn on routing on the SupIV? BGP is routing protocol

30 remote offices averaging 10 people per office that are connecting via a MPLS network to the 2851.



Re: Where to put the default gateway for best performance

I assume you mean should you run a routing "protcol" on the sup. I hope you are letting the sup do the routing between the vlans by turning on ip routing but just do not have something like BGP configured.

Your default gateway should go to the location that has the most networks connected to it. In most cases this will be a internet gateway.

In your case it appears you have 2 major groups of networks. The 2851 and 4507. If the 4507 has the internet connection it can just advertise the default route to the 2851 and the 2851 can advertise all his networks to the 4507. If you wish the 2851 can just send the default route to the remote location. If the 2851 has the internet connection then it needs to be the destination for any default route.

If you don't worry about internet if for example your company forces all traffic via a proxy server then you can not even use the default route. It will depend on how big your routing table is and the size of your lines. If you use BGP it is a very low bandwidth protocol in a stable network. Default route is used in a environemnt where you do not want to use a lot of bandwidth just to keep routing updated. The goal of the default route is to reduce the number of networks advertised so it is placed in the device with the most networks.

Community Member

Re: Where to put the default gateway for best performance

Sorry, not that default route or gateway.

Here is an example.

I have 10 VLANS

VLAN 10 default gateway is Data

VLAN 11 default gateway is Voice

VLAN 12 default gateway is Server


Should I assign these IP address of the default gateway for each vlan on a VLAN interface on the 4507R or assign them to a sub interface on the 2851 Gigabit Ethernet interface.

NO intervlan routing on the switch. My vote iss to assign them to a vlan interface on the 4507R. The designer/consultant wants to use sub interfaces on the 2851.

Also, We will be running a IP Phones in their own VLAN with COS/QOS. I don't know if this changes things but thought I would add that.

Thanks you for the update. I


Re: Where to put the default gateway for best performance

I am not really familliar with all the models of the 4500 but I though there were basically 2 types. Basic and full fuction with the primary difference being if they run routing protcol like OSPF,EIGRP etc.

I am under the impression that they all can route between vlans on the switch.

I can see no reason to run router on a stick with a 2851. It is kinda silly for the traffic to go out a port and back in when it can just cross a internal bus in the switch.

If these are like most other cisco switches the basic version can even run rip so routing could be exchnaged with the 2851 over a point to point if there was some need.

If they make 4500 models that are pure layer 2 then you have no option. The default gateway for the segement must reside on a layer 3 device to route traffic between them.

Community Member

Re: Where to put the default gateway for best performance

They just added BGP support last month.

The Sup IV modules support OSPF, EIGRP, BGP

They are layer 3

You have been very helpful. I will rate your post as such.


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