Changing ttl of incoming packets

[Niki Denev]

Ruslan Ermilov writes:

> On Thu, Apr 22, 2004 at 11:54:15AM +0200, GiZmen wrote:
>> Hello,
>>  
>> 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?
> 
> 
> Cheers,
> -- 
> Ruslan Ermilov
> ru at FreeBSD.org
> FreeBSD committer

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

--niki
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