We have 4 branch offices connected thru 100mbps link with Cisco 2600 routers which has the throughput of 15mbps.
Now I am planning to replace these routers with Cisco 2901G2 ISR routers which has the throughput of 167mbps.
So if I replace the routers at one location first is it going to put more load on other routers as the new routers can handle more traffic than other 2600 routers? Should I replace all routers at once?
Yes, it will shape your traffic as 20 mbps average.
You can only apply Shaping on outgoing direction.
You can check how policy working by "sh policy-map int" and sh int.
It is possible that new router in one location will send out more traffic to other branches if users sends out more traffic from this new location to other location.
But, you can prevent this with shaping policy applied to your new router's outgoing interface if you experience this issue.
service-policy pm-shape out
shape average 15000000
So, I would replace one location first and monitor.
If you find congestion on other location as new router sends out more than 15 mbps, then you can apply above shape policy to restrict new router's capability until all locations are upgraded.