For a long time now, I have been allowing IPIP only from registered
gateways and
disallowed nested IPIP. Indeed I have seen in the past that IPIP
packets were sent with
the intention of being forwarded through "allow trusted subnets" rules
and then maybe
back out to internet hosts that were targeted for DDoS or similar.
When looking in the logs of those rules, I usually see dropped packets
from hosts that
are apparently on dynamic addresses and have changed address, but this
change has
not yet reached me through the ampr-rip announcements.
However, there are indeed also instances of apparently unrelated
intrusion attempts.
It remains my position that we should change from this IPIP mesh to a
more modern
VPN system where stations with dynamic addresses can participate through
a local
VPN server that participates in a network that uses standard protocols
to form a
dedicated AMPRnet tunnel network with automatic routing, that can be
used by standard
equipment and can be made more resilient against unwanted use (e.g. by
using GRE/IPsec
and L2TP/IPsec tunnels instead of the traditional IPIP).
However, I no longer want to beat a dead horse. We had the discussion a
while ago but
unfortunately it was then redirected onto a separate mailing list.
Rob