The Routing Table

Welcome to part 2 in a 3 part series of articles about routers and routing . If you have arrived here directly through a search engine you may wish to read Part 1 – How Does a Router Work? first. Here we are going to look at the routing table. All network devices that use the TCP/IP protocol have a routing table, even your Windows PC has one. ALL devices use their routing table to determine where to send packets. Without a routing table your PC wouldn’t even be able to communicate with computers on the same subnet. Here is a screenshot of the routing table of my PC. To see your own routing table open a command prompt by typing CMD in the run or search box. Then at the command prompt type “”route print” and press enter.

By |2020-02-02T18:16:23+10:00August 24th, 2011|Categories: TCP/IP|Tags: , , , , |6 Comments

Why Multiple VPN Connections To The Same IP Fail

In a previous article I explained what PPTP passthrough is and how it works. In this article I will explain why multiple VPN connections fail with certain routers. This issue only affects PPTP connections and it is directly related to PPTP passthrough. Here is a brief comparison of how NAT handles PPTP VPN connections differently to normal connections. Read the PPTP passthrough link above for more details: When computers make normal outbound connections the source IP address is NATed to the public IP. Source ports are used  to uniquely identify the multiple connections. When PPTP clients make outbound connections the same thing happens but the call ID AND destination IP is used instead of source ports to uniquely identify the VPN connections.

By |2020-02-02T18:16:23+10:00August 9th, 2011|Categories: TCP/IP|Tags: , , , , , |7 Comments

PPTP Passthrough and How It Works

Most computers connect to the Internet through a NAT device (usually a router). PPTP natively doesn’t work with NAT. Since most VPN connections start from behind a router this is a very common problem. PPTP passthrough addresses this by allowing VPN connections to traverse a NAT with ease. NAT (or more specifically PAT) can’t function without the use of ports. It is important you understand how NAT functions and it’s reliance on ports. If unsure I would advise reading up on network address translation first. NOTE: With some routers multiple VPN connections is not supported.

By |2020-02-02T18:16:24+10:00July 28th, 2011|Categories: TCP/IP|Tags: , , , , , |11 Comments

How A Router Works (and IP routing)

Welcome to part 1 in a 3 part series of articles about routers and routing. In part 1 we will cover how routers works, part 2 talks about the routing table and part 3 covers IP routing. So, how does a router work? Well, before we get into that you should know the basics of what the IP address is, subnet mask and default gateway before continuing. If you don’t have a read of networking basics first.

By |2020-02-07T16:34:12+10:00July 18th, 2011|Categories: TCP/IP|Tags: , , , |8 Comments