…"how should I design this szenario. Should I use the AP ? Where should I put it to?"...
Do you want the linksys and the pfSense system to both be wirelessly directly connected to your mesh? And, they will be in separate locations? Otherwise, if they are near each other, only one needs to be on the wireless mesh and functioning as a wireless "AP"; thus, the second unit would be connected to the first via ethernet/wired. So, configure routing as normal, and add an HNA route announcement in OLSR for the second unit's IP & netmask.
Freifunk/olsr for Linksys WRT54GL...
http://212.222.128.68/sven-ola/ipkg/g+gl/
To also use it as an "access point", update it with this package: "freifunk-dnsmasq..*_mipsel.ipk" from...
http://212.222.128.68/sven-ola/ipkg/packages/
If you want wireless dhcp to Not use NAT and serve "real routed" IPs to local wireless clients then ssh (or PuTTY) into your linksys, you'll need to backup copy and delete /etc/dnsmasq.conf then recreate it because it's just a reference to a rom file, edit /etc/dnsmasq.conf with "vi" editor and add an extra "dhcp-range" line for device "wlnat" and configure the desired dhcp IP range and netmask (restrict range to your node's IPs) for wireless clients, also comment out lines begining with "address=", and if you set up "olsr nat" in the gui then erase it. [update] Newer versions may require DNS server IPs to be specified in dnsmasq.conf.
If you need more help check the Freifunk mailing list…
http://freifunk.net/pipermail/wlanware/
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As for OLSR on pfSense:
sample olsr & dnsmasq configs...
http://forum.pfsense.org/index.php/topic,677.msg8294.html#msg8294
plus add startup shell scripts such as these for olsrd & dnsmasq ...
http://forum.pfsense.org/index.php/topic,677.msg8180.html#msg8180
Pete
ipro.net, inc.
pc@ipro.net