rsmurf6: command not found

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 CentOS possible default full paths are:

/usr/bin/rsmurf6 - from package: thc-ipv6

You may install the required package with command yum install {package}

Error in other languages:
rsmurf6: bevel nie gevind nie
rsmurf6: comandă negăsită
rsmurf6: comando não encontrado
rsmurf6: commande introuvable
rsmurf6: command not found
rsmurf6: käsku ei ole
rsmurf6: không tìm thấy lệnh
rsmurf6: komanda nerasta
rsmurf6: Kommando nicht gefunden.
rsmurf6: kommandot finns inte
rsmurf6: komut yok
rsmurf6: nie znaleziono polecenia
rsmurf6: níor aimsíodh an t-ordú
rsmurf6: no se encontró la orden
rsmurf6: no s'ha trobat l'ordre
rsmurf6: opdracht niet gevonden
rsmurf6: parancs nem található
rsmurf6: perintah tidak ditemukan
rsmurf6: príkaz nenájdený
rsmurf6: příkaz nenalezen
rsmurf6: команда не найдена
rsmurf6: командата не е открита
rsmurf6: 命令找不到
rsmurf6: コマンドが見つかりません