Reduce traffic load on WAN router by routing internal vlans via switches?

[mitchen]

Hi,

we have a remote site with a 3750 Switch stack and voice and data VLANs set-up.  The inter-VLAN routing is currently provided by a Cisco 1841 router which also provides WAN connectivity (via IPSEC VPN connection) with 3 other sites.

As we have started various activities which have led to an increase in traffic going through the router, we are finding that the CPU utilisation on the Cisco 1841 router runs very high at times and this causes degradation in service for our user (e.g. momentary loss of network connectivity, voice calls dropping/suffering from poor quality, etc)

We tried replacing the 1841 router with a 2811 but found the CPU ran high on it too.

So I'm looking for ways of alleviating the traffic load on the router - and thought that we could perhaps pass the interVLAN routing to the switch stack rather than passing it through the router for processing?

Would this be possible/advisable?  We are running the IP Base image on our switch stack.

Thanks.

[garapoglou]

Hi,

Before performing any changes to interVLAN routing, have you checked QoS?

Since you use VoIP, you really have to configure QoS first. Otherwise you will have to deal with delay or even jitter.

Have you checked the CPU utilization during the problem? Is there data available?

Best regards,

Giorgos

[mitchen]

Hi Giorgos,

thanks for the reply.

Yes, we have QoS configured.  We are also running IP SLA between the sites and measuring MOS and ICPIF values, etc.

But I'm convinced the problem is definitely due to the CPU utilisation rather than any QoS or bandwidth issues or anything - it ties in perfectly, whenever we have issues the CPU has hit 100%

However, I am unsure what else I can do to try to alleviate some of the strain on the CPU (I've done the usual such as turned off any logging on ACLs etc) but felt that if I could at least have the traffic flow between the internal VLANs processed by the switches instead of the router, it may at least reduce some of the burden on the router.

Any further advice welcomed!

[garapoglou]

You're welcome, Mitchen!

I'm pretty sure the CPU has hit the top when problems occur. It's very interesting that replacing the 1841 with the 2811 didn't improve the situation even a little bit.

The next step would be to change the interVLAN routing then. Since you have a 3750 switch stack, you should try configuring it on the switch stack instead.

But I think you should also check the CPU load during the problem, if it's possible. I would definitely do it.

Giorgos