Programming – G1FEF

Turning POE on and off on the Cisco 3750 via SNMP

G1FEF — Sat, 08 Sep 2018 09:03:07 +0000

I recently had a requirement to be able to turn the POE power off / on on specific ports on a remote c3750 POE switch in order to reboot devices that kept crashing.

I had been remotely logging in via SSH and doing the following to turn the power off on port 1:


configure terminal
interface FastEthernet1/0/1
power inline never
exit
exit

Then after a few seconds:


configure terminal
interface FastEhernet1/0/1
no power inline never
exit
exit

This got to be a real nuisance so I looked for something that I could script, SNMP seemed the logical choice. The first step is to configure a R/W community string on the switch:


configure terminal
snmp-server community MyCommunityString rw
exit
write memory

After a bit of digging I found the appropriate OID by using snmpwalk (here we assume my switch is on IP address 1.2.3.4):


snmpwalk -v2c -On -c MyCommunityString 1.2.3.4 1.3.6.1.2.1.105.1.1.1.3.1

My 24 port switch returned the following:

.1.3.6.1.2.1.105.1.1.1.3.1.3 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.4 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.5 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.6 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.7 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.8 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.9 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.10 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.11 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.12 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.13 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.14 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.15 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.16 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.17 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.18 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.19 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.20 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.21 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.22 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.23 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.24 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.25 = INTEGER: 1
.1.3.6.1.2.1.105.1.1.1.3.1.26 = INTEGER: 1

The port number go from .3 to .26 corresponding to the 24 FastEthernet ports.

The integer values need to be 1 to enable POE and 2 to disable it.

So using snmpset we can turn the power on port 1 off:


snmpset -v2c -c MyCommunityString 1.2.3.4 1.3.6.1.2.1.105.1.1.1.3.1.7 i 2

and back on again:


snmpset -v2c -c MyCommunityString 1.2.3.4 1.3.6.1.2.1.105.1.1.1.3.1.7 i 1

That’s it! Simple really. Adding the commands to a script I will leave to the imagination of the reader…

GNU screen scrollback and other navigation

G1FEF — Sun, 16 Apr 2017 13:25:33 +0000

GNU screen commands

The GNU screen program has some useful navigation facilities. To enter COPY MODE you need to press CTRL + A + [

Once in copy mode use the keys below to navigate:

h	Move the cursor left by one character
j	Move the cursor down by one line
k	Move the cursor up by one line
l	Move the cursor right by one character
0	Move to the beginning of the current line
$	Move to the end of the current line
G	Moves to the specified line
C-u	Scrolls a half page up
C-b	Scrolls a full page up
C-d	Scrolls a half page down
C-f	Scrolls the full page down

When starting screen you can set the size of the scrollback buffer by using the -h command line argument, for example to set the scrollback buffer to 1000 lines:

screen -h 1000

This can also be set in .screenrc with defscrollback

Adding a new SVN repo

G1FEF — Thu, 23 Mar 2017 14:51:54 +0000

How to create a new SVN repository

On the local machine the svn server is on:

Create the new repo:

# svnadmin create /path/to/repo/reponame

Change ownership to web daemon:

# chown -R apache.apache /path/to/repo/reponame

Switch to svn account:

# su - svn

Edit policy file to give users access:

# vim .svn-policy-file

Add access to the repo, e.g.

[reponame:/]
username = rw

Now a new project can be committed to the repo.

To upload an existing directory tree from a server:

Create new, empty folder in repo:
- svn mkdir https://svn.host.com/svn_path/newApp
Go to parent directory on server
Checkout the repo over your existing folder:
- svn co https://svn.host.com/svn_path/newApp
Use svn add to add new files
Use commit to upload