Hello .. Packet path :)

Hello .. Packet path :)

[Michael Gale]

Hello,

	I am trying to make a packet go through the least amount of chains / tables as possible for performance.

I have read through the online documentation about netfilter and this "Linux Firewalls Second Edition" book (which was ok). 

But I still have some questions about the order in which the tables are checked. Here is what I think happens when a pack comes in and should be forwarded to a internal machine

Firewall External interface:
Packet comes in:
NAT table PREROUTING 
NAT talbe OUTPUT
NAT table POSTROUTING
filter table INPUT
filter table OUTPUT or forward

Then you would have the same thing when the packet leaves the internal interface.

Of course this is if you break it down by interface first.

Please let me know if this is correct ?

-- 
Michael Gale
Network Administrator
Utilitran Corporation

Re: Hello .. Packet path :)

[Ramin Dousti]

Daniel Chemko had an email on this subject not too long ago:
 
Raw/PREROUTING
Mangle/PREROUTING
Nat/PREROUTING
Mangle/INPUT
Filter/INPUT
Mangle/FORWARD
Filter/FORWARD
Raw/OUTPUT
Mangle/OUTPUT
Filter/OUTPUT
Nat/OUTPUT
Mangle/POSTROUTING
Nat/POSTROUTING
 

On Wed, Dec 03, 2003 at 08:30:34AM -0700, Michael Gale wrote:

> Hello,
> 
> 	I am trying to make a packet go through the least amount of chains / tables as possible for performance.
> 
> I have read through the online documentation about netfilter and this "Linux Firewalls Second Edition" book (which was ok). 
> 
> But I still have some questions about the order in which the tables are checked. Here is what I think happens when a pack comes in and should be forwarded to a internal machine
> 
> Firewall External interface:
> Packet comes in:
> NAT table PREROUTING 
> NAT talbe OUTPUT
> NAT table POSTROUTING
> filter table INPUT
> filter table OUTPUT or forward
> 
> Then you would have the same thing when the packet leaves the internal interface.
> 
> Of course this is if you break it down by interface first.
> 
> Please let me know if this is correct ?
> 
> -- 
> Michael Gale
> Network Administrator
> Utilitran Corporation

Re: Hello .. Packet path :)

[Michael Gale]

Thank you to all who replied :)

Michael.


On Wed, 3 Dec 2003 11:46:47 -0500
Ramin Dousti <ramin@cannon.eng.us.uu.net> wrote:

> Daniel Chemko had an email on this subject not too long ago:
>  
> Raw/PREROUTING
> Mangle/PREROUTING
> Nat/PREROUTING
> Mangle/INPUT
> Filter/INPUT
> Mangle/FORWARD
> Filter/FORWARD
> Raw/OUTPUT
> Mangle/OUTPUT
> Filter/OUTPUT
> Nat/OUTPUT
> Mangle/POSTROUTING
> Nat/POSTROUTING
>  
> 
> On Wed, Dec 03, 2003 at 08:30:34AM -0700, Michael Gale wrote:
> 
> > Hello,
> > 
> > 	I am trying to make a packet go through the least amount of chains / tables as possible for performance.
> > 
> > I have read through the online documentation about netfilter and this "Linux Firewalls Second Edition" book (which was ok). 
> > 
> > But I still have some questions about the order in which the tables are checked. Here is what I think happens when a pack comes in and should be forwarded to a internal machine
> > 
> > Firewall External interface:
> > Packet comes in:
> > NAT table PREROUTING 
> > NAT talbe OUTPUT
> > NAT table POSTROUTING
> > filter table INPUT
> > filter table OUTPUT or forward
> > 
> > Then you would have the same thing when the packet leaves the internal interface.
> > 
> > Of course this is if you break it down by interface first.
> > 
> > Please let me know if this is correct ?
> > 
> > -- 
> > Michael Gale
> > Network Administrator
> > Utilitran Corporation
> 


-- 
Michael Gale
Network Administrator
Utilitran Corporation