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Re: fastroute

On Tue, 3 Jun 2003, Marco Grigull wrote:
> A feature that might be useful to others would be to set the ttl to a defined
> value, or adjust it for hiding not so capable routers.
> 'ttl -2'	decremnt it by 2, probably useless
> 'ttl 64'	re/set it to 64, hiding a variety of OSes on the network
> 'ttl +1'	increment it by 1, hiding this firewall and an inner or outer router
> 'ttl 0'		aka fastroute
If you want to have a hidden firewall, you should make it a bridge.
PF already has some way to adjust the TTL of packets:
1) scrub has an option min-ttl to enforces a minimum TTL for matching IP
2) -current has scrub reassemble tcp. pf.conf(4) explains what it does
      Statefully normalizes TCP connections.  scrub reassemble tcp rules
      may not have the direction (in/out) specified.  reassemble tcp per-
      forms the following normalizations:
      ttl      Neither side of the connection is allowed to reduce their
               IP TTL.  An attacker may send a packet such that it reach-
               es the firewall, affects the firewall state, and expires
               before reaching the destination host.  reassemble tcp will
               raise the TTL of all packets back up to the highest value
               seen on the connection.
Dries Schellekens
email: [email protected]