Help with Load Balancing Default Routes out

[Guest_imported]

We are a medium sized ISP. We have 4 T1's that come in for bandwidth. 2 are from Sprint and 2 are from SBIS. In my router I have the following for routes out


ip route 0.0.0.0 0.0.0.0 Serial2/0 Sprint1
ip route 0.0.0.0 0.0.0.0 Serial1/0 Sprint2
ip route 0.0.0.0 0.0.0.0 Serial1/1 SBIS1
ip route 0.0.0.0 0.0.0.0 Serial2/1 SBIS2

On the interfaces I have ip route-cache enabled. and currently all traffic is going Sprint 1 and Sprint 2 nothing has even hit the SBIS1 and SBIS2. Is there a way that I can load balance the traffic going out?

 

[4mo]

Since ip route-cache is enabled you are using Fast Switching.(Cisco default)
Fast switching will balance traffic on a per destination basis. Packet's with the same destination will flow out the same interface. Depending on your traffic pattern you may get uneven distribution. But you will have low CPU utiliztion and faster switching times.

If you enter "no ip route-cache" you will now be process switching.
Process switching will load balance per packet. The first packet is sent out the interface of the first route. Second Packet out the second and so on, round robin fashion. The cost will be very high CPU utilization and slow switching times.

Jeff Doyle's "Routing TCP/IP Volume I" covers this on pages 110-112

Regards,
Matt

 

[wybnormal]

Look at my serial FAQ here in this forum I give some suggestions to load balancing static maps. Also, consider policy routing where you can either have it by protocol or by ip range to use a certain serial interface.

::from FAQ:::
Static routes allow you to set up load balancing after a fashion. Keep in mind that the IOS load balances across routes first and not interfaces. The easiest way to configure multiple routes on the same interface is to use the secondary IP command

Router 1
!
interface serial 0
ip address 192.0.0.1 255.255.255.0
ip address 192.0.0.2 255.255.255.0 secondary ! second route on same interface

interface serial 1
ip address 192.1.0.1 255.255.255.0
ip address 192.1.0.2 255.255.255.0 secondary

ip route 200.2.0.0 255.255.255.0 196.0.0.4; goes to serial 0
ip route 200.2.0.0 255.255.255.0 196.0.0.5; goes to serial 0
ip route 200.2.0.0 255.255.255.0 196.1.0.4; goes to serial 1

Router 2
!
interface ethernet 0
ip address 200.2.0.1 255.255.255.0
!
interface serial 0
ip address 196.0.0.4 255.255.255.0
ip address 196.0.0.5 255.255.255.0 secondary
!
interface serial 1
ip address 196.1.0.4 255.255.255.0
ip address 196.1.0.5 255.255.255.0 secondary


The traffic would go out router 1 across the two IPs on serial 0 first then across 1 IP on serial 1
This gives you unequal load balancing.
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