$ nix-shell -p 'enableDebugging iproute'
$ gdb ip
(gdb) b main
Breakpoint 1 at 0x408d60: file ip.c, line 172.
(gdb) r route
Starting program: /nix/store/x7gjcsxd48fp1wnpwjidqpn7nar4483y-iproute2-4.15.0/bin/ip route

Breakpoint 1, main (argc=2, argv=0x7fffffffc6e8) at ip.c:172
172	ip.c: No such file or directory.