change packets with IPFW divert

[Julian Elischer]

On 19/10/2016 1:56 PM, Samira Nazari wrote:
>   Thank you for all of your comments and help.
> In fact, I want to divert packets for one program that do header compression


What kind of header compression? Also look at netgraph.
>
> Sam, Naz
>
> On Tue, Oct 18, 2016 at 7:33 PM, Ian Smith <smithi at nimnet.asn.au> wrote:
>
>> On Tue, 18 Oct 2016 14:21:50 +0000, Shawn Bakhtiar wrote:
>>   > On Oct 18, 2016, at 6:49 AM, Samira Nazari <nazari.s11 at gmail.com
>> <mailto:nazari.s11 at gmail.com>> wrote:
>>   > > Hello every one,
>>   > > When we diverte packets to the specified port with "IPFW divert" ,
>>   > > we can change it and re-sent to the kernel?
>>
>>   > Not sure what you mean by change it but:
>>   >
>>   > "Divert sockets are similar to raw IP sockets, except that they can
>>   > be bound to a specific divert port via the bind(2) system call.  The
>>   > IP address in the bind is ignored; only the port number is
>>   > significant.  A divert socket bound to a divert port will receive all
>>   > packets diverted to that port by some (here unspecified) kernel
>>   > mechanism(s).  Packets may also be written to a divert port, in which
>>   > case they re-enter kernel IP packet processing."
>>   >
>>   > -- SRC: https://www.freebsd.org/cgi/man.cgi?query=divert&sektion=
>> 4&apropos=0&manpath=FreeBSD+10.3-RELEASE+and+Ports
>>
>> Apart from divert(4), most likely the best example is the natd(8) code,
>> which modifies packet source or destination addresses and (maybe) ports.
>>
>> Ignoring the NAT processing - or not, as appropriate - the way natd uses
>> divert sockets both to receive packets from ipfw and later (perhaps) to
>> reinject them for further processing should show clearly how it's done.
>>
>> cheers, Ian
>>
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