Linux-kernel mailing list archive 2000-07,: Re: Firewall packet logging question?

# Re: Firewall packet logging question?

William Stearns (wstearns@pobox.com)
Wed, 16 Feb 2000 09:10:48 -0500 (EST)

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Good morning, Mike,

On Wed, 16 Feb 2000, Mike A. Harris wrote:

> Does the current kernel (2.2.x) have any provisions for logging
> or capturing the ENTIRE IP packet which matches a particular
> ipchains rule?
> [snip]
> need to patch the kernel to implement this, or does the kernel
> include a mechanism (which I think it does) to do this allready?
>
> Instead of the packets getting logged by the kernel somewhere, it
> would be acceptable for them to be passed to a user level daemon
> for processing and logging if necessary.

You can pass it to userspace for further analysis. From man
ipchains:

-o, --output [maxsize]
Copy matching packets to the userspace device. This is currently mainly
for developers who want to play with firewalling effects in userspace.
The optional maxsize argument can be used to limit the maximum number of
bytes from the packet which are to be copied. This option is only valid
if the ker<AD> nel has been compiled with CONFIG_IP_FIREWALL_NETLINK set.

, and from a (possibly old) 2.2 kernel Configure.help:

CONFIG_IP_FIREWALL_NETLINK
If you say Y here, you can use the ipchains tool to copy all or part
of any packet you specify that hits your Linux firewall to optional
user space monitoring software that can then look for attacks and
take actions such as paging the administrator of the site.
To use this, you need to create a character special file under /dev
with major number 36 and minor number 3 using mknod ("man mknod"),
and you need (to write) a program that reads from that device and
takes appropriate action.

The ipchains mailing list at
http://www.starshadow.com/mailman/listinfo/ipchains is probably a better
place is you have additional questions.
Cheers,
- Bill

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