Welcome to LQ.
Are you using a "bgp patched" ns-2.xx version ?
I don't think there is any "get-bgp-agent" with a default ns2 version.
"get-bgp-agent" is present in the bgp files select.tcl,
and ns-2.34/tcl/test/bgp/<files>.tcl from `ns-2.34-bgp_2.0_patch´.
Can you please attach 'FRRT.tcl' as FRRT.tcl.txt ?
Attachments : The paper clip tool in the 'Advanced Editor'.