ip default-network is not a default route.
Try
R1:
ip route 0.0.0.0 0.0.0.0 192.168.102.3
and
R2:
ip route 192.168.100.0 255.255.255.0 192.168.102.4
ip route 192.168.101.0 255.255.255.0 192.168.102.4
ip route 0.0.0.0 0.0.0.0 se0/0 (or whaterver the serial interface is).
Also, you should have NAT configured on R2 if you want these subnets to access the Internet.
Hope this helps,
Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
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