Originally Posted by doctorcisco

Hello All,

I'm running a 2.4 Linux kernel on a Linksys router (OpenWRT), and need to set up a GRE tunnel from this box to a Cisco router. I've installed the kernel package on the Linky. ip tunnel mytunnel mode gre local 1.2.3.4 remote 2.3.4.5 ttl 32 (etc etc) works just fine.

Here's my problem: the IP address on my DSL line changes about every 2 days. With this configuration, the GRE tunnel goes down until I manually update the config on both ends.

Is there any way to use an interface name or DNS name instead of an IP for the "remote" subcommand? (Analagous to "ip unnumbered int vlan1" on a Cisco box?)

Barring that, is there a way to get Linux to:

a) Notice a changed IP (maybe a cron job to whatismyip.com or something.)
Yes.

b) Automagically reconfigure its GRE tunnel whenever it decides its IP address has changed?
Yes.

I can use tcl/expect on a server in the LAN to go update the Cisco. Any way to get the Linksys to do the job by itself?
On Debian, there is a directory called /etc/ppp, in this directory are two other directories, ip-up.d and ip-down.d. There are man pages for this stuff but to cut to the chase, anytime that PPPd brings up the ppp interface, all the scripts in /etc/ppp/ip-up.d will be run in lexical order, write a bash with a name such that it is run after all the other scipts in this directory to bring up your tunnel.
Wirte a bash script to bring down the tunnel and delete the tunnal with an appropriate name to run after all the scripts in the /etc/ppp/ip-down.d directory.

Now, these ppp entries "may" be particular to Debian but each distro will have equivalent things so just look around your directories, you find what you need.

That should solve your problems.

Cheers,
john
Thanks,
doctorcisco