Changing ttl of incoming packets

[GiZmen]

> >> 
> >>Is there any way to change ttl of incoming packet to a lower value ?
> >>I had tried min-ttl option in pf packet filter but this option only 
> >>increase
> >>ttl to a given value when ttl is lower than this value.
> >> 
> >>I have searched on google and mailing lists but i do not find any answer.
> >>I am running Freebsd 5.2.1 and i am using pf as my packet filter.
> >> 
> >You mean, make the IP forwarding decrement the IP TTL more than by one?
> i've seen some cable/dsl ips's to do this, they set the IP TTL to 1 on the 
> downlink to the client. (as a lame attempt to stop people sharing their 
> connection)
> So if one put some sort of gateway on the dsl/cable modem, all 
> the packets it receives are with IP TTL 1, and the gateway will not able to 
> forward them to the internal network....... which is in my opinion 
> 1-st ugly, and 2-nd, easily avoidable with min-ttl for example :)
> but if pf has min-ttl it seems that max-ttl can be easily added.
> also i think i've seen somewhere on the net a netgraph module that can 
> modify ttl's and some other things. i think it's name was ng_mangle
---end quoted text---

Yes true i saw some gateways that use this trick too and that was my inspiration
to look around how it can be done. But i didnt found any option to do that.
max-ttl option would be a good idea to add to pf :)
So there is no posibility to change ttl with kernel or some other tool.
So how this dsl/cable modem gateways change theirs ttl to 1?

thx
-- 
Best Regards:
		GiZmen

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