tftp – Penumbra

In this short howto I’ll explain how to use expect scripts with Cisco devices. In this example I’m going to use it to backup the current running configuration.

Requirements

A working tftp server

Expect

Lucky for us both requirements are available in all major distro’s.

The Debian/Ubuntu way:

sudo apt-get install tftp tftpd expect

Next on our todo list is configuring the tftp server. This should also be fairly easy:

# cat /etc/xinetd.d/tftp
service tftp
{
    protocol        = udp
    port            = 69
    socket_type     = dgram
    wait            = yes
    user            = nobody
    server          = /usr/sbin/in.tftpd
    server_args     = /tftpboot
    disable         = no
}

Restart your xinetd server when done.

# /etc/init.d/xinetd restart

Make sure the /tftpboot folder exists and is owned by user and group nobody:

# chown -R nobody:nobody /tftpboot

You should also create an empty file where you’d like to save your configuration and rerun the above command to adjust permissions.

# touch /tftpboot/config
# chown -R nobody:nobody /tftpboot

You should also create an empty file where you’d like to save your configuration and rerun the above command to adjust permissions.

# touch /tftpboot/config
# chown -R nobody:nobody /tftpboot

We can now test our newly configured tftpd server:
Create a new file in your home dir called config and put some random text in it.

# cat /home/user/config
test 12

# tftp
tftp> open localhost
tftp> put config
Sent 146 bytes in 0.0 seconds

# cat /tftpboot/config
test 12

Excellent! We’re ready to receive config files from the Cisco device.

Below you will find an example script:

#!/usr/bin/expect

## TomDV
## http://blog.penumbra.be/2010/02/expect-scripts-backup-cisco-config/

# ---------------- configuration ---------------- #
set device 192.168.0.100    # cisco device
set tftp 192.168.0.200      # tftp server
set user someuser           # username
set pass ultrasecret        # password
set config                  # config destination
set timeout 60

# -------------- do not edit below -------------- #
spawn telnet $device
expect "Password:"
send "$pass\n"
expect ">"
send "en\n"
expect "Password:"
send "$pass\n"

send "copy running-config tftp://$tftp/$config\n\n"
expect "$tftp"
send "\n"
expect "$config"
send "\n"
send "exit\n"

Save it anywhere you like and run it from the shell. You’ll see something like this in your logs:

user in.tftpd[22304]: connect from 192.168.0.200 (192.168.0.200)
user tftpd[22305]: tftpd: trying to get file: config
user tftpd[22305]: tftpd: serving file from /tftpboot

That’s it. Your current Cisco config has been saved to /tftpboot/config.

I wouldn’t recommend using this into production without proper firewalling. You can get the same results by using snmp. But that’s however a subject for another howto.

Tag: tftp

Using expect scripts to backup your Cisco configuration