README

Backroute
=========

Backroute is a lightweight shell script, that monitors a primary router, and
switches to a backup router and back as the primary router comes back online.
Backroute is for you, if you want to have automatic router failover to a backup
router, but want to avoid the complexities of dynamic routing daemons.

Typical usage scenario:

* you have a new, fast (ADSL oder cable) internet connection, which sometimes
  may fail.
* you have a backup internet connection (ISDN or even modem), which is not used
  anymore.
* you have a linux server, which handles things like dhcp, smb filesharing, www
  proxy, etc.

Principle of operation:

* The linux server is entered as the default gateway of all clients. Since the
  linux server adapts it's routing automatically, clients will no longer notice
  when the fast router goes offline.
* Automatic changing of the linux server's routing table:
  o a static route to the next upstream router is entered into route.conf.
  o backroute shell script is called regulary as a cron job and:
    it checks the next upstream router
    + if upstream router fails, the routing table is changed to switch to
      default route to the backup router
    + if upstream router is back online, the routing table is changed to the
      fast router

Download

Version 1.1: backroute.tar

Backroute is licensed under GPL. Also check out the project page at
www.freshmeat.net


Installation:

* Copy copy backroute.sh to a directory of you choice, e.g. /usr/local/sbin.
* Enter a static route to the next upstream router of your ISP into
  the routing table (e.g. /etc/route.conf). 
  Use the traceroute command to find out the next router's
  "upstream" IP address. Your routing table should look something like this
   (212.254.x.y is my next upstream router, my backup router is 192.168.1.1)

   andromeda:~/tools # route -n
   Kernel IP Routentabelle
   Ziel          Router        Genmask         Flags Metric
   212.254.x.y   192.168.1.253 255.255.255.255 UGH 0 0 0 eth0
   192.168.1.0   0.0.0.0       255.255.255.0   U 0 0 0 eth0
   0.0.0.0       192.168.1.1   0.0.0.0         UG 0 0 0 eth0
    

* Configuration of backroute.sh is via constant defintions in backroute.sh.
  o Enter "upstream" IP adress in backroute.sh (212.254.x.y in my example)
  o Enter the ip address of your fast router as "fastrouter" in backroute.sh. 
    A default route to $fastrouter will be set, if $upstream is reachable.
  o Enter the ip address of your backup router "backrouter" in backroute.sh. 
    A default route to $backrouter will be set, if $upstream is not reachable.
  o When a $upstream changes state, a log entry will be written to the textfile
    $fastlog. Also, a mail will be sent to mail address $mailto
  o I prefer to enter all numerical IP's in the hosts table. Because of this,
    only hostnames apear in my script, no numerical adresses.

* Test your backroute.sh by calling it on the command line. If your $upstream is
  down, it will delay 5 seconds, then write an entry to $fastlog. Check your
  routing table using route -n.

* Create a cron job file /etc/cron.d/backroute, that is called frequently (once
  a minute in my case). The tarfile contains an example for this. 

  >>CUT
  0-59/1 * * * * root /usr/local/sbin//backroute &
  >>CUT

* Once everything is running, you should do the following to allow all clients
  to profit from high-availability routing:
  o Enable IP forwarding (see your system manual for how to turn this on)
  o Set to default gateway of all your clients to your linux box. The best way
    is of course via dhcp.

Caveats:
========

* As you switch routers, your clients may experience problems when sending mail,
  This is because your ISP's smtp server will not accept mail if you come from an
  "alien" IP.

Fix: since a mailserver (postfix in my case) is already running on your linux
box, just set it to relay mails of your local clients. Your linux box will then
deliver all mail to the right isp smarthost. I recommend this because you will run 
into problems if you run full mailserver without smarthost from a dialin ip (certain
mailservers will simply drop all mail from dialin ips!). If you have two different
isp's on the two routers, you may have to switch mailserver configs and restart your
mailserver. Version 1.1 has support for this, however having 3 config files is 
certainly not very pretty. On the other hand, i didn't want my script edit
foreign config files, and possibly mess them up. So my solution is to have two
versions of the mailserver config files with different smarthosts, and copy them 
to the active config file. Afterwards, the mailserver is reloaded so that the 
new config takes effect. This runs nicely at my site. But be shure to change the
right config files!


Comments

Please, send in any bugs or comments to backroute@epr.ch