Re: change packets with IPFW divert

[Samira Nazari]

RTP header compression

On Thu, Nov 3, 2016 at 11:41 AM, Julian Elischer  wrote:

> 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  wrote:
>>
>> On Tue, 18 Oct 2016 14:21:50 +, Shawn Bakhtiar wrote:
>>>   > On Oct 18, 2016, at 6:49 AM, Samira Nazari >> > 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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>>
>>
>
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Re: 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  wrote:


On Tue, 18 Oct 2016 14:21:50 +, Shawn Bakhtiar wrote:
  > On Oct 18, 2016, at 6:49 AM, Samira Nazari mailto:nazari@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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Re: change packets with IPFW divert

[Samira Nazari]

 Thank you for all of your comments and help.
In fact, I want to divert packets for one program that do header compression

Sam, Naz

On Tue, Oct 18, 2016 at 7:33 PM, Ian Smith  wrote:

> On Tue, 18 Oct 2016 14:21:50 +, Shawn Bakhtiar wrote:
>  > On Oct 18, 2016, at 6:49 AM, Samira Nazari  > 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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Re: change packets with IPFW divert

[Ian Smith]

On Tue, 18 Oct 2016 14:21:50 +, Shawn Bakhtiar wrote:
 > On Oct 18, 2016, at 6:49 AM, Samira Nazari 
 > mailto:nazari@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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Re: change packets with IPFW divert

[Shawn Bakhtiar]

On Oct 18, 2016, at 6:49 AM, Samira Nazari 
mailto:nazari@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?
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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





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