Re: Changing ttl of incoming packets

From: GiZmen (gizmen_at_blurp.one.pl)
Date: 04/23/04

  • Next message: GiZmen: "Re: Changing ttl of incoming packets" 
    Date: Fri, 23 Apr 2004 02:34:21 +0200
To: freebsd-hackers@freebsd.org

    > >>
    > >>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
UNIX is user-friendly; it's just picky about its friends
UNIX is simple; it just takes a genius to understand its simplicity
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  • Next message: GiZmen: "Re: Changing ttl of incoming packets"

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