Mike,
DD-WRT is not known to provide a method to compile/install the necessary software (i.e. a RIP44 routing daemon). Aside from this, I cannot recall if a tunnel can be established. Nonetheless, if you were to succeed standing up a tunnel, you'd need the routing daemon to properly configure your reply traffic. This routing daemon concern may be overcome by employing a Munge Script (hopefully DD-WRT has some tools like: `curl`, `ftp`, `grep`, `fgrep`, `sed`, `sort` and `diff` installed in the firmware).
https://wiki.ampr.org/wiki/Munge_script
You can start testing using commands from the startampr, OpenWrt, Ubuntu and/or Linux setup guides on the Wiki. Feel free to ask any questions (when you can stand up a tunnel). I've never used the Munge Script method, I'm sure others have (I should note that there's a script posted that can parse the encap.txt file - it's located on the Firewall page). The `ip tunnel` commands in `startampr` should be of help to test establishing the tunnel.
https://wiki.ampr.org/wiki/Startampr#Script
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- Prior to using OpenWrt, I personally forwarded IPENCAP (IP Protocol No. 4) to a gateway running Ubuntu Server. - https://wiki.ampr.org/wiki/Firewalls#DD-WRT - Also see "Static IPENCAP Filtering of AMPR Nodes" here: https://wiki.ampr.org/wiki/Firewalls#iptables
73,
- Lynwood
KB3VWG