Hello,
The message "warning:Route to base_stn not known: dropping pkt" is generated
by the mobile node's DSDV agent (see ns/dsdv/dsdv.cc). DSDV agent always
tries to send packets to the base station referred in the variable base_stn_
of the class MobileNode (see ns/mobilenode.cc). In wireless3.tcl, with the
instruction
set HAaddress [AddrParams set-hieraddr [$HA node-addr]]
[$MH set regagent_] set home_agent_ $HAaddress
we set base_stn_ with the address of the home agent.
When the mobile node performs a handoff, after receiving a new agent
advertisement (from the foreign agent), it modifies the value of base_stn_
with the address of the foreign agent (see mip-reg.cc).
The warning message is caused because the mobile node is trying to send a
packet (probably an acknowledgement to a received TCP packet) to the old
base station, but it is not under its coverage area and it has not updated
the value of base_stn_ yet.
I hope it helps,