[CentOS] Packet routing diagram

[Ljubomir Ljubojevic]

Kenneth Porter wrote:
> There's a number of diagrams around the Internet illustrating the path 
> packets take through the Linux kernel, including the various firewall 
> modules, that's quite helpful in understanding which rules should go in 
> which table.
> 
> Here's one that's not bad:
> 
> <http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch14_:_Linux_Firewalls_Using_iptables#Figure_14-1_Iptables_Packet_Flow_Diagram>
> 
> The box labeled "Local Processing of Data" is where packets that are 
> created by the firewall's applications originate.
> 
> Does anyone have a better diagram? How about one that shows the policy 
> routing system?

Maybe this one:
http://www.shorewall.net/NetfilterOverview.html

Policy routing is pretty straightforward. You mark the packet in PREROUTING:

iptables -t mangle -A PREROUTING -d 172.27.0.0/16 -j MARK --set-mark 200

, and then add (ip )route rules like in: 
http://www.policyrouting.org/PolicyRoutingBook/ONLINE/CH05.web.html#5.6

I use policy routing only on StarV3 Wireless/LAN routers and they very 
easy to set up policy routing:

policy nfmark 80 {default 10.0.1.100 }
or
policy from 192.168.2.0/24 { default 10.10.1.1 }
policy to 192.168.2.0/24 { default 10.10.1.1 }
etc...

Ljubomir
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