Category Archives: Netfilter

iptables mangle and NAT notes, etc.


PREROUTING in mangle table: alter routing (e.g. source-based routing)
FORWARD in mangle table: traffic shaping for tc (flowid)

In MikroTik RouterOS, /ip firewall nat:
srcnat chain = PREROUTING
dstnat chain = POSTROUTING

/ip firewall mangle:
prerouting chain = global-in
forward chain = global-out (support NAT traffic shaping, higher load on router)

Update: I used to think that global-in literally means global input, while global-out literally means global output.  Apparently I was mistaken.  The parent queues MUST be matched to the right parent, either global-in, global-out, global-total, or one of the network interfaces depending on the mangle rules.  Top-most queue parent (global-in, global-out, global-total) doesn’t decide whether it’s up/down.  The mangle rules do the direction decision trick, whether a packet is incoming/download or outgoing/upload.  This makes perfect sense now! (doh)  I kept wondering why half of my queues (download queues’ top-most parent was global-in) weren’t working, when all my mangle rules were in forward chain.  Obviously they wouldn’t, because global-in marks both direction in prerouting chain.

Update 2: mangle: download rules first then upload rules. global-in, connection mark: prerouting; packet mark: prerouting. global-out, connection mark: forward, packet mark: postrouting.


This didn’t make sense until I read the URL listed below under References.  Silly me!  Assumption is the root of most, if not all, problems indeed.


ipt_account HOWTO for Fedora Core 6

For the last few days I have been looking for a bandwidth monitoring tool that is more efficient, accurate, and complete than IPFM. I found so many bandwidth monitoring tools (bandwidthd, ipband, darkstat, and a few others) on Google but couldn’t find one that fits what I want. In fact, IPFM suits me better than the others.

While I was reading iptables’ man page, I accidentally came across ‘account’ under ‘MATCH EXTENSIONS’. After reading the brief description and example, I got excited! This iptables match extension provides exactly what I need! With the flexibility of iptables’ rules plus the account match extension, this has to be the best solution for my new bandwidth monitoring system. There is one problem though. Fedora Core doesn’t have it. 🙁

With some experience I got from installing ipp2p by hand, I started trying to make this iptables match extension work on my Fedora Core 6 server. First, I used Google to locate ipt_account’s website. Then I used Google to search for some install guides on ipt_account but couldn’t find any, so I went through its website and found something.

Since I have prepared my system with kernel & iptables source tree, rpmbuild, etc. (basically everything required to build ipp2p modules), I will not go over the “ingredients” again. Sorry!

Download the kernel and iptables patches from this page. Patch the kernel tree:

  • cd /usr/src/redhat/BUILD/kernel-2.6.19/linux-2.6.19.i386/
  • patch -p1 < path_to_kernel_patch

You should see the following:

patching file include/linux/netfilter_ipv4/ipt_account.h
patching file net/ipv4/netfilter/ipt_account.c
patching file net/ipv4/netfilter/Kconfig
patching file net/ipv4/netfilter/Makefile

OK, now the kernel tree is patched. Now do make oldconfig. You will be asked:

account match support (IP_NF_MATCH_ACCOUNT) [N/m/?] (NEW)

Since this will be a kernel module, hit m. Once the process has finished, do make scripts/kconfig/ (if you haven’t previously during ipp2p module build process). Create a temporary directory somewhere (e.g. /tmp/ipt). Copy /usr/src/redhat/BUILD/kernel-2.6.19/linux-2.6.19.i386/net/ipv4/netfilter/ipt_account.c into that directory and create a file named Makefile. Paste the following into Makefile:

obj-m := ipt_account.o
KDIR := /usr/src/redhat/BUILD/kernel-2.6.19/linux-2.6.19.i386/
PWD := $(shell pwd)
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

Make sure that there is a tab before $(MAKE). Save the file and execute make. If the compile process goes well, there will be a file named ipt_account.ko in the directory. Load the module by using insmod. Check lsmod to see the newly loaded module.

If you have got this far, that means your kernel now supports ipt_account. Now we will add ipt_account extension for iptables. To see if your iptables has ipt_account support, do iptables -m account. If it prints out something like “Couldn’t load match `account’: …”, that means there is no iptables account extension yet.

Let’s patch iptables source tree:

  • cd /usr/src/redhat/BUILD/iptables-1.3.5
  • patch -p1 < path_to_iptables_patch

Expect the following:

patching file extensions/libipt_account.c

Open extensions/Makefile, on line 8, add account before ah. Then compile the ipt_account’s extension:

cc -O2 -Wall -Wunused -I/usr/src/redhat/BUILD/kernel-2.6.19/linux-2.6.19.i386/include -Iinclude/ -DIPTABLES_VERSION=\”1.3.5\” -fPIC -o extensions/libipt_account_sh.o -c extensions/libipt_account.c
cc -shared -o extensions/ extensions/libipt_account_sh.o

Copy extensions/ to /lib/iptables and verify the extension: iptables -m account. That’s it! Pretty easy, eh? 🙂

Read this page to test the new iptables account match extension. Enjoy!

ipp2p HOWTO for Fedora Core 6

While this post is titled “for Fedora Core 6”, it may be applicable to previous versions of Fedora Core. I tested this on Fedora Core 4 too, but some steps are different.
Note: This guide uses iptables-1.3.5-1.2.1 and kernel-2.6.19-1.2895.fc6.

First, grab ipp2p-0.8.2.tar.gz or the latest version if there’s any. Extract the tarball and make sure you have iptables and the currently installed kernel’s SRPMs installed. To proceed, I recommend rpm-build to be installed (simply use yum to install, i.e. yum install rpm-build). Next, install both SRPMs using the following command: rpm -ivh file.rpm. If you get “error: cannot create %sourcedir /usr/src/redhat/SOURCES” message, you can create the required directory: mkdir -p /usr/src/redhat. Also, rpm-building the kernel source requires redhat-rpm-config and unifdef to be installed.
Now that the “ingredients” are ready, let’s start doing the fun part..

Go to /usr/src/redhat/SPECS and do rpmbuild -bp iptables.spec, this will prepare the iptables’ source tree to match with the currently installed iptables binaries’ source. Do the same for the kernel, rpmbuild -bp kernel-2.6.spec. The newly patched source tree can be found inside /usr/src/redhat/BUILD directory.

Grab symvers-2.6.19-1.2895.fc6.gz from /boot, gunzip and rename it as Module.symvers, then move it to the kernel’s source directory (/usr/src/redhat/BUILD/kernel-2.6.19/linux-2.6.19-i386). Go into that directory, make sure that existing kernel config (.config) exists, then do: make scripts/kconfig/.
Note: If you can’t find symvers file in /boot, install kernel-devel package and you will find Module.symvers in /usr/src/kernels//.

Next, return to the ipp2p source directory and do two modifications.




KERNEL_SRC ?= $(firstword $(wildcard …


IPTABLES_SRC = /usr/src/redhat/BUILD/iptables-1.3.5


ifeq ($(IPTABLES_SRC),)

Save the changes and do make.

If it compiles successfully, then ipt_ipp2p.ko and should be in the directory now.
Copy to /lib/iptables. To verify whether this iptables module works, do iptables -m ipp2p -h.
In case you get the following: iptables v1.3.8: Couldn’t load match `ipp2p’, don’t worry. Have a look at this solution and simply recompile the modules.

There are two ways to load the ipp2p kernel module, insmod ipt_ipp2p.ko or copy ipt_ipp2p.ko to /lib/modules/2.6.19-1.2895.fc6/kernel/net/ipv4/netfilter and do depmod -a.