My goal is to be able to do something like this:

curl google.com --interface ppp0

curl google.com --interface p2p2

ppp0 is a DSL connection, and p2p2 is a separate direct Internet connection. Currently I can only get one of these to work at a time. When I enable one, the other one stops working.

/etc/network/interfaces:

# The loopback network interface
auto lo
iface lo inet loopback

# DSL
auto p2p1
iface p2p1 inet manual

auto dsl-provider
iface dsl-provider inet ppp
pre-up /sbin/ifconfig p2p1 up # line maintained by pppoeconf
provider dsl-provider

# DIRECT
auto p2p2
iface p2p2 inet dhcp

ifconfig:

lo        Link encap:Local Loopback  
inet addr:127.0.0.1  Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING  MTU:65536  Metric:1

p2p1      Link encap:Ethernet    
inet6 addr: fe80::20a:ebff:fe21:99c6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

p2p2      Link encap:Ethernet  
inet addr:192.168.1.101  Bcast:192.168.1.255  Mask:255.255.255.0
inet6 addr: fe80::20a:ebff:fe17:1249/64 Scope:Link
UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

ppp0      Link encap:Point-to-Point Protocol  
inet addr:53.193.231.167  P-t-P:53.193.224.1  Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1492  Metric:1

route -n

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         0.0.0.0         0.0.0.0         U     0      0        0 ppp0
10.0.10.0       0.0.0.0         255.255.255.0   U     0      0        0 eth2
53.193.224.1    0.0.0.0         255.255.255.255 UH    0      0        0 ppp0
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 p2p2

By default, only ppp0 works. If I run "route add default gw 192.168.1.1 p2p2" then I can use p2p2 but ppp0 stops working. If I then run "route add default gw 53.193.224.1 ppp0" then I can use ppp0 again but p2p2 stops working.

What can I do to be able to use both interfaces selectively?