xorp_fib2mrib: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/lib/xorp/sbin/xorp_fib2mrib - from package: xorp

You may install the required package with command apt-get install {package}
Error in other languages:
xorp_fib2mrib: bevel nie gevind nie
xorp_fib2mrib: comandă negăsită
xorp_fib2mrib: comando não encontrado
xorp_fib2mrib: commande introuvable
xorp_fib2mrib: command not found
xorp_fib2mrib: käsku ei ole
xorp_fib2mrib: không tìm thấy lệnh
xorp_fib2mrib: komanda nerasta
xorp_fib2mrib: Kommando nicht gefunden.
xorp_fib2mrib: kommandot finns inte
xorp_fib2mrib: komut yok
xorp_fib2mrib: nie znaleziono polecenia
xorp_fib2mrib: níor aimsíodh an t-ordú
xorp_fib2mrib: no se encontró la orden
xorp_fib2mrib: no s'ha trobat l'ordre
xorp_fib2mrib: opdracht niet gevonden
xorp_fib2mrib: parancs nem található
xorp_fib2mrib: perintah tidak ditemukan
xorp_fib2mrib: príkaz nenájdený
xorp_fib2mrib: příkaz nenalezen
xorp_fib2mrib: команда не найдена
xorp_fib2mrib: командата не е открита
xorp_fib2mrib: 命令找不到
xorp_fib2mrib: コマンドが見つかりません