[LARTC] load balancing between two default gateways

[Askar]

Hi list gurus,
long story short we have firewall machine which is the default gateway 
for our clients and firewall send traffic out to Internet via cisco router.
On cisco we have two serial interfaces 1Mb and 2Mb.
On firewall
#route add default gw xxx.xxx.xx.xxx (for 2mb)
#route add default gw xxx.xxx.xx.xxx (for 1mb)
and the same rule for Imb link route packets via these two links.
However I don't know what kernel do when sending traffic via these two 
"default routes" however im sure kernel not doing some sorta shapping, 
coz after few hours of these two rules our 1mb link got chocked and we 
have to "route delete default gw xxx.xxx.xx (1mb).

Now what I want may be "shapping" to route 70% traffic via 2Mb and 30 
via 1Mb.
Is this possible via iproute2? if yes I will greatly appreciate if 
someone helps newbie to iproute2 :)

regards
Askar