Quickly find changes in network configurations files with diff
The diff utility is excellent for quickly spotting changes in network configuration files. After all major network changes, upgrades, or maintenance this is one of my staple commands to validate there are no unexpected changes. It is especially helpful for router configurations that are thousands of lines long.
Start with a quick overview of what changed, by running diff with no options:
jemurray@mbp-2019:~ $ diff previous-config.txt current-config.txt
60c60
< username jemurray privilege 15 password 0 CiscoLab123
---
> username jemurray privilege 15 password 0 CiscoLab
87a88
> description Uplink Interface
94d94
< description shutdown
Find specific differences line-by-line in side-by-side mode, by running: diff -W 120 -y previous-config.txt current-config.txt
- -W: sets the width to 120 characters. Adjust as necessary to fit the full configuration on a single screen.
- -y: side-by-side
Differences in the files are indicated by the following symbols:
- <: line is in the previous file, but not current.
-
: line is in the current file, but not previous.
- |: line is in both files, but changed.
jemurray@mbp-2019:~ $ diff -W 120 -y previous-config.txt current-config.txt
csr100v#show run csr100v#show run
Building configuration... Building configuration...
Current configuration : 3382 bytes Current configuration : 3382 bytes
! !
! Last configuration change at 03:11:05 UTC Tue May 19 2 ! Last configuration change at 03:11:05 UTC Tue May 19 2
! !
version 15.7 version 15.7
service timestamps debug datetime msec service timestamps debug datetime msec
service timestamps log datetime msec service timestamps log datetime msec
no service password-encryption no service password-encryption
! !
hostname csr100v hostname csr100v
! !
boot-start-marker boot-start-marker
boot-end-marker boot-end-marker
! !
! !
! !
aaa new-model aaa new-model
! !
! !
aaa authentication login default local aaa authentication login default local
! !
! !
! !
! !
! !
aaa session-id common aaa session-id common
! !
! !
! !
mmi polling-interval 60 mmi polling-interval 60
no mmi auto-configure no mmi auto-configure
no mmi pvc no mmi pvc
mmi snmp-timeout 180 mmi snmp-timeout 180
! !
! !
! !
! !
! !
no ip icmp rate-limit unreachable no ip icmp rate-limit unreachable
! !
! !
! !
! !
! !
! !
no ip domain lookup no ip domain lookup
ip domain name example.com ip domain name example.com
ip cef ip cef
no ipv6 cef no ipv6 cef
! !
multilink bundle-name authenticated multilink bundle-name authenticated
! !
! !
! !
! !
username jemurray privilege 15 password 0 CiscoLab123 | username jemurray privilege 15 password 0 CiscoLab
! !
redundancy redundancy
! !
no cdp log mismatch duplex no cdp log mismatch duplex
! !
ip tcp synwait-time 5 ip tcp synwait-time 5
! !
! !
! !
! !
! !
! !
! !
! !
! !
! !
! !
! !
! !
interface GigabitEthernet0/0 interface GigabitEthernet0/0
no ip address no ip address
shutdown shutdown
duplex auto duplex auto
speed auto speed auto
media-type rj45 media-type rj45
! !
interface GigabitEthernet0/1 interface GigabitEthernet0/1
> description Uplink Interface
ip address dhcp ip address dhcp
duplex auto duplex auto
speed auto speed auto
media-type rj45 media-type rj45
! !
interface GigabitEthernet0/2 interface GigabitEthernet0/2
description shutdown <
no ip address no ip address
shutdown shutdown
duplex auto duplex auto
speed auto speed auto
media-type rj45 media-type rj45
! !
interface GigabitEthernet0/3 interface GigabitEthernet0/3
no ip address no ip address
shutdown shutdown
duplex auto duplex auto
speed auto speed auto
media-type rj45 media-type rj45
! !
ip forward-protocol nd ip forward-protocol nd
! !
! !
no ip http server no ip http server
no ip http secure-server no ip http secure-server
ip ssh version 2 ip ssh version 2
! !
ipv6 ioam timestamp ipv6 ioam timestamp
! !
! !
! !
! !
! !
control-plane control-plane
! !
banner exec ^C banner exec ^C
******************************************************** ********************************************************
* IOSv is strictly limited to use for evaluation, demons * IOSv is strictly limited to use for evaluation, demons
* education. IOSv is provided as-is and is not supported * education. IOSv is provided as-is and is not supported
* Technical Advisory Center. Any use or disclosure, in w * Technical Advisory Center. Any use or disclosure, in w
* of the IOSv Software or Documentation to any third par * of the IOSv Software or Documentation to any third par
* purposes is expressly prohibited except as otherwise a * purposes is expressly prohibited except as otherwise a
* Cisco in writing. * Cisco in writing.
******************************************************** ********************************************************
banner incoming ^C banner incoming ^C
******************************************************** ********************************************************
* IOSv is strictly limited to use for evaluation, demons * IOSv is strictly limited to use for evaluation, demons
* education. IOSv is provided as-is and is not supported * education. IOSv is provided as-is and is not supported
* Technical Advisory Center. Any use or disclosure, in w * Technical Advisory Center. Any use or disclosure, in w
* of the IOSv Software or Documentation to any third par * of the IOSv Software or Documentation to any third par
* purposes is expressly prohibited except as otherwise a * purposes is expressly prohibited except as otherwise a
* Cisco in writing. * Cisco in writing.
******************************************************** ********************************************************
banner login ^C banner login ^C
******************************************************** ********************************************************
* IOSv is strictly limited to use for evaluation, demons * IOSv is strictly limited to use for evaluation, demons
* education. IOSv is provided as-is and is not supported * education. IOSv is provided as-is and is not supported
* Technical Advisory Center. Any use or disclosure, in w * Technical Advisory Center. Any use or disclosure, in w
* of the IOSv Software or Documentation to any third par * of the IOSv Software or Documentation to any third par
* purposes is expressly prohibited except as otherwise a * purposes is expressly prohibited except as otherwise a
* Cisco in writing. * Cisco in writing.
******************************************************** ********************************************************
! !
line con 0 line con 0
exec-timeout 0 0 exec-timeout 0 0
privilege level 15 privilege level 15
logging synchronous logging synchronous
line aux 0 line aux 0
exec-timeout 0 0 exec-timeout 0 0
privilege level 15 privilege level 15
logging synchronous logging synchronous
line vty 0 4 line vty 0 4
privilege level 15 privilege level 15
transport input ssh transport input ssh
line vty 5 15 line vty 5 15
privilege level 15 privilege level 15
transport input ssh transport input ssh
! !
no scheduler allocate no scheduler allocate
! !