There are a couple of things you can do to accomplish what you want as far as load balancing goes. One is to use ppp multilink to bond them together as a single pipe. Here is a link on that:
http://www.cisco.com/warp/public/793/access_dial/mpp_serial.html
You can ignore the Bridge group information and ipx information in the example, what is relevent to you is the virtual-template and ppp configurations under the serial interfaces. You can also load balance the following way:
Under each serial interface configure:
no ip route-cache
no ip mroute-cache (if it lets you)
load-interval 30 (you can remove this later by typing: no load-interval 30)
under Global Config (CONFIG T):
Turn off CEF (if it is on)
add 2 gateway of last resort addresses:
ip route 0.0.0.0 0.0.0.0 (next hop ip of first serial)
ip route 0.0.0.0 0.0.0.0 (next hop ip of second serial)
Press: CTRL Z
type: WRITE MEM (to save config)
Either way, your links should start to load balance.
You can do a show interface and look at the LOAD (or txload and rxload) under each serial
interface...and also check the 5 minute input and output rates (which now say 30 second, since we changed it with the load interval command) You data should balance going out of your router, but you have no control over how it comes back in and so your receive loads may not balance. Whomever is on the remote end of the router would also have to configure their router to do load balancing back in your direction in order to get both tx and rx loads to balance.
Both ways will provide redundancy if a link goes down, but this second way is better then with ppp multilink.I hope that answers your question.
