I don't know if your router has a direct DSL interface or not, but you'll be better of terminating the telephone line / DSL line on a regular DSL modem which your ISP provides and is willing to troubleshoot.
Then connect the Ethernet cables between the 2801 ports and the DSL modems.
Keep DSL in bridge mode, and terminate the PPPoE (if your provider has this, it mostly is this way), and use a Dialer Interface as the outside interface.
You will have two default routes , one pointing to each next hop.
You'll have to NAT your inside pool to both public blocks, with route-maps, with match interface.
Please note, load-balancing will not be per packet, but will be per flow (source ip , destination ip pair).
To know which flow will take which path, use:
Router#show ip cef exact-route 192.168.1.20 126.96.36.199
Also, load-balancing wouldn't be cummulative due to the above fact.
So , if you have one link with 7 Mbps, and the other with 5 Mbps, don't expect to open a speedtest site and hope to see 7+5=12 Mbps speed. If it takes the 7 Mbps link, thats the max you get, else 5Mbps.
However, will multiple sessions / PCs that will be sending flows, and if they are statistically balanced / random flows, you should see both links being almost equally utilized.
A similar , scenario is discussed here (mainly for the nat config part)
We are pleased to announce availability of Beta software for 16.6.3.
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Introduction Featured Speakers Luis Espejel is the Telecommunications
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