One of the locations I look after has a stack of 16 Cisco switches that I manage remotely via the Internet. These switches often undergo some very complicated reconfigurations for certain customers of the site and from time to time I have found myself locked out via Telnet and have had to visit site with a serial console cable to put the configurations right.
To avoid any more of these unplanned site visits I decided to sort out a serial console server for this site. If your reading this you probably realize that a Serial Console server is basically a computer with a number of Serial Interfaces and an Ethernet port. You can connect to the console server and the out over one of its serial ports to control the attached devices.
I needed a device with 16 ports. Proper 16-port console servers like those produced by Avocent cost upwards of £1500, so I decided to build my own. I put together the cheapest barebones PC system i could find with a spare PCI-Express slot. Into this spare PCI-E Slot i Installed a Startech 16-port PCI-E Serial Card. (PEX16S952LP) shown below.
Startech PEX16S952LP
I then dug around the storerooms and found 16 standard blue Cisco Serial console cables and connected them from the 16-port breakout cable coming from the serial card and into each of the switches. I installed Ubuntu Server on the system. I could see 16 ttySx devices in /dev/ and i could use minicom to connect to the switch on the end of each /dev/ttySx port. The next stage, expose these serial ports via Reverse Telnet for easy remote management.
The ubuntu package ser2net package describes itself as:
This daemon allows telnet and tcp sessions to be established with a
unit’s serial ports. Combined with a terminal emulation like xterm or
the Linux console, this can be a very simple means of communicating
with routers, other systems’ serial consoles and other equipment with
a serial port. This is remarkably similar to the reverse telnet
feature of some Cisco routers.
I installed the package with:
sudo apt-get install ser2net
The next step is to configure which TCP ports you want ser2net to listen on and which serial ports to map these to. This is done in /etc/ser2net.conf my configuration file looks something like this:
BANNER:banner:\r\nser2net port \p device \d [\s] (Debian GNU/Linux)\r\n\r\n 2000:telnet:600:/dev/ttyS0:9600 8DATABITS NONE 1STOPBIT banner 2001:telnet:600:/dev/ttyS1:9600 8DATABITS NONE 1STOPBIT banner 2002:telnet:600:/dev/ttyS2:9600 8DATABITS NONE 1STOPBIT banner 2003:telnet:600:/dev/ttyS3:9600 8DATABITS NONE 1STOPBIT banner 2004:telnet:600:/dev/ttyS4:9600 8DATABITS NONE 1STOPBIT banner 2005:telnet:600:/dev/ttyS5:9600 8DATABITS NONE 1STOPBIT banner 2006:telnet:600:/dev/ttyS6:9600 8DATABITS NONE 1STOPBIT banner 2007:telnet:600:/dev/ttyS7:9600 8DATABITS NONE 1STOPBIT banner 2008:telnet:600:/dev/ttyS8:9600 8DATABITS NONE 1STOPBIT banner 2009:telnet:600:/dev/ttyS9:9600 8DATABITS NONE 1STOPBIT banner 2010:telnet:600:/dev/ttyS10:9600 8DATABITS NONE 1STOPBIT banner 2011:telnet:600:/dev/ttyS11:9600 8DATABITS NONE 1STOPBIT banner 2012:telnet:600:/dev/ttyS12:9600 8DATABITS NONE 1STOPBIT banner 2013:telnet:600:/dev/ttyS13:9600 8DATABITS NONE 1STOPBIT banner 2014:telnet:600:/dev/ttyS14:9600 8DATABITS NONE 1STOPBIT banner 2015:telnet:600:/dev/ttyS15:9600 8DATABITS NONE 1STOPBIT banner
Once ser2ner has been restarted with /etc/init.d/ser2net restart i was able to telnet into ports 2000 through to 2015 and gain direct access to the serial port connected to each switch.
