Parsing Cisco Switche config using TCL and shell script

Extracting Cisco Configurations Using TCL and Bash

Today I’d like to talk about extracting Cisco configurations—such as switches, routers, ASA, etc.—from network devices to your Linux machine for further manipulation.

To achieve this, I wrote two scripts:

1. A TCL script for exporting or configuring Cisco devices
2. A Bash script for manipulating the extracted data in a fairly complex way

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Overview

We’ll start with the TCL script. I downloaded part of it from a website and modified it, since TCL can be quite cryptic for me 🙂.

What the TCL script does:

• Retrieves the VLAN brief
• Saves the output to a log file
• Retrieves interface status
• Executes a Bash script to parse the generated files

This approach can be used for large-scale deployments. You can even push configurations through a TCL script, although I avoided that here since it is very similar to manually entering passwords or executing shell commands.

I hope this will be useful for some people and educational for others 🙂

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What the TCL Script Does (Step by Step)

To simplify things, the TCL script performs the following actions:

• Connects to a Cisco device (in my case, a switch stack)
• Sends the login password, then enters enable mode with the enable password
• Starts logging and disables the Cisco pager to get full output without interaction
• Executes show vlan brief to retrieve VLAN ID, description, name, and ports
• Stops logging after writing results to a file
• Starts logging to a different file and disables the pager again
• Executes show interfaces status to retrieve interface name, VLAN ID, and status
• Stops logging and executes a Bash script to parse the generated files
• Requires the IP address to be passed as an argument when executing the script

---

TCL / Expect Script

#!/usr/bin/expect -f
#!/bin/bash

set force_conservative 1 ;
# set to 1 to force conservative mode even if
# script wasn't run conservatively originally

if {$force_conservative} {
    set send_slow {1 .1}
    proc send {ignore arg} {
        sleep .1
        exp_send -s -- $arg
    }
}

set timeout 3000
log_user 1

set var1 [lindex $argv 0]
set var2 [lindex $argv 1]

puts $var1
puts $var2

spawn ssh -1 -l username $var1
match_max 100000

expect "*assword: " {send -- "password1\r"}
sleep .5

expect ">"
send -- "en\r"

expect "*assword:" {
    send -- "password2\r"
}

log_file /root/scripts/vlans_per_id
expect "#" {send -- "term len 0\r"}
expect "#" {send -- "sh vlan brief\r"}
expect "#" {send -- "\r"}
sleep .5
log_file

log_file /root/scripts/vlans_per_interface
expect "#" {send -- "term len 0\r"}
expect "#" {send -- "sh interfaces status\r"}
expect "#" {send -- "\r"}
expect "#" {send -- "exit\r"}
expect "#" {send -- "exit\r"}
log_file

exec /bin/bash parser.sh $var1
exit

---

What the Bash Script Does

The Bash script performs the following steps:

• Reads the vlans_per_id file and removes leftovers (headers and footers) from the TCL log
• Reads the switch hostname and generates a file named after the hostname
• Writes the hostname and IP address of the switch into the file header
• Reads vlans_per_interface, removes speed and duplex information, and replaces VLAN IDs with VLAN names using data from vlans_per_id
• Generates a third file named switch_hostname.map

---

Notes

• awk is used to replace vlan_id with vlan_name
• All intermediate generated files are deleted, keeping only the necessary output
• The parser was written in Bash because I’m comfortable with Bash scripting
• awk and sed are used in different ways for educational purposes
• The script could be written in many different ways, but this approach was chosen for clarity and learning—so please excuse me, geeks of the world 🙂

---

Bash Parser Script

#!/bin/bash -x
# Prepared by sghaida
# Date: Wed Mar 21 21:11:48 EET 2012

FILE=vlans_per_id
VLANS=vlans_per_interface

sed -i -e '1,2d' $FILE
sed -i -e '2,4d' $FILE
sed -i -e '$d' $FILE

DICTIONARY=$(cat $FILE | head -n 1 | awk -F\# '{print $1}')
sed '1d' $FILE > $DICTIONARY
rm -rf $FILE

echo "Hostname   : $DICTIONARY" > $DICTIONARY.MAP
echo "IP Address : $1" >> $DICTIONARY.MAP
echo "" >> $DICTIONARY.MAP
echo -e "port \t vlan \t status" >> $DICTIONARY.MAP
echo "" >> $DICTIONARY.MAP
echo -e "---- \t ---- \t ------" >> $DICTIONARY.MAP
echo "" >> $DICTIONARY.MAP

sed -i -e '1,5d' $VLANS
sed -i -e '$d' $VLANS
sed -i -e '$d' $VLANS
sed -i -e '$d' $VLANS

cat $VLANS | awk '{print $1 "\t\t" $3 "\t\t" $2}' > $VLANS.TMP
mv $VLANS.TMP $VLANS

while read line; do
    vlan_id=$(echo $line | awk '{print $2}')

    if [ "$vlan_id" == "trunk" ]; then
        vlan_name="trunk"
        continue
    fi

    while read another_line; do
        vlan_id2=$(echo $another_line | awk '{print $1}')
        vlan_name2=$(echo $another_line | awk '{print $2}')

        if [ "$vlan_id" -eq "$vlan_id2" ]; then
            vlan_name=$vlan_name2
            break
        fi
    done < $DICTIONARY

    echo -e "$line" | awk -v v1="$vlan_name" -v v2="$vlan_id" \
        '{ sub(v2,v1,$2); print $1 "\t" $2 "\t" $3 }' >> $DICTIONARY.MAP

done < $VLANS

rm -rf $VLANS