Designing and Implementing Linux Firewalls with QoS using netfilter, iproute2, NAT and L7-filter

Designing and Implementing Linux Firewalls with QoS using netfilter, iproute2, NAT and L7-filter

Language: English

Pages: 288

ISBN: 1904811655

Format: PDF / Kindle (mobi) / ePub


This practical guide teaches you how to implement effective network protection by using your own customized firewall solution. Based on extensive practical experience, this book distills a unique set of scenario based scripts and guidelines for a proven firewall solution, into one succinct and precise book. This book is aimed at Linux Network administrators with some understanding of Linux security threats and issues, or any one interested in securing their systems behind a firewall. Basic knowledge of Linux is presumed but other than that this book shows you how to do the rest, from configuring your system to dealing with security breaches.

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Modprobe for NAT to work. The OUTPUT chain is not fully supported, so we will have to ignore that for now. The PREROUTING and POSTROUTING chains have meaningful names. The PREROUTING chain is analyzed by the kernel before any routing decision is made. Therefore, what we should do in the PREROUTING chain is to change the address of the destination IP and then leave it to the routing process to find the destination that we just changed (DNAT). The POSTROUTING chain contains rules that the.

PAT or NAPT). iptables –t nat –A PREROUTING –d 1.2.4.2 –p tcp –-dport 65521 –j DNAT –-to 192.168.1.100:22 This way, when we are not at the office and we want to SSH into the intranet server, we open an SSH connection to 1.2.4.2 port 65521. After a while, suppose we installed a web server with the IP address 192.168.1.200. The web server is www.mycompany.whatever and points in DNS to 1.2.4.5. To be accessible to the outside world, we perform the following: iptables –t nat –A PREROUTING –d.

-j REDIRECT --to-port 3128 #Masquerade HTTPS for children's computer $IPT -t nat -A POSTROUTING –o eth0 -s 192.168.1.55 -p tcp --dport 443 -j MASQUERADE #Masquerade the children's computer for DNS requests $IPT -t nat -A POSTROUTING -o eth0 -s 192.168.1.55 -p udp --dport 53 -j MASQUERADE [ 146 ] Chapter 6 #Masquerade the children's computer to access yahoo messenger servers $IPT -t nat -A POSTROUTING -o eth0 -s 192.168.1.55 -d scs.msg.yahoo. com -j MASQUERADE $IPT -t nat -A.

Most important things about security are knowing your network, building it in an intelligent manner and with security in mind, and most of all, understanding how packets flow in your network. Understanding the flow of the packets in the network is essential for people who want to build good firewalls and intelligent QoS. I've seen simpler networks than the ones presented here with very complicated firewalls, which had rules that didn't belong there or that could be reduced to much simpler.

That the packets leave those routers with the correct DSCP marks, but they come into Core-4 with the TOS byte 0x0. So what do those links have in common? They are both MPLS services, and most MPLS-enabled switches and routers clear the TOS byte. Talking to Provider-2's engineers and explaining the problems, they could solve the issue, and the EoMPLS connection keeps our DSCP marks. However, Provider-1's engineers could not do the same thing for the MPLS VPN connection, but they managed to.

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