[LARTC] Multiipath routing - can't ping links from LAN after default routes

[Ming-Ching Tiew]

I have a Linux with 3 LAN interfaces doing multipath
NAT to two internet links via ADSL. The question I
have is after I added the default route on each of the
routing table, I can't ping the external interfaces of the
Linux from the LAN ( pinging from the Linux itself is
OK ). But pinging beyond the two external interfaces
( eg the default route  ) is OK.

I use symbolic names here :-
   #
   ip route add ${INSIDE_NETWORK}      dev ${INSIDE_DEV}              table
first
   ip route add ${OUTSIDE_NETWORK}   dev ${OUTSIDE_DEVICE}  table first
   ip route add ${OUTSIDE_NETWORK2} dev ${OUTSIDE_DEVICE2} table first
   ip route add 127.0.0.0/8          dev lo              table first
   #
   ip route add ${INSIDE_NETWORK}      dev ${INSIDE_DEV}          table
second
   ip route add ${OUTSIDE_NETWORK}  dev ${OUTSIDE_DEVICE}  table second
   ip route add ${OUTSIDE_NETWORK2} dev ${OUTSIDE_DEVICE2} table second
   ip route add 127.0.0.0/8          dev lo              table second
   #
   ip route add ${OUTSIDE_NETWORK}   dev ${OUTSIDE_DEVICE}   src
${OUTSIDE_IP}
   ip route add ${OUTSIDE_NETWORK2} dev ${OUTSIDE_DEVICE2} src
${OUTSIDE_IP2}
   #
   ip rule add from ${OUTSIDE_IP}   table first
   ip rule add from ${OUTSIDE_IP2} table second
  #
  # weighted multipath routing
  #
  ip route add default scope global nexthop via \${OUTSIDE_GATEWAY} \
 ${OUTSIDE_DEVICE}  weight ${OUTSIDE_DEV_WEIGHT} \    nexthop
${OUTSIDE_GATEWAY2} dev ${OUTSIDE_DEVICE2} \
 weight ${OUTSIDE_DEV2_WEIGHT}

Everything is working if I just do as above, I can ping OUTSIDE_GATEWAY
and OUTSIDE_GATEWAY2 AND OUTSIDE_IP and OUTSIDE_IP2. But
If I added the two lines below :-

   ip route add default via ${OUTSIDE_GATEWAY}  table first
   ip route add default via ${OUTSIDE_GATEWAY2} table second

Then I can't ping from my INSIDE_NETWORK to both the OUTSIDE_IP
and OUTSIDE_IP2 but still able to ping OUTSIDE_GATEWAY
and OUTSIDE_GATEWAY2.

Why ?