You can assign it an IP address, run routing protocols on it, or configure it for static routes. It behaves like any other interface.įrom a Layer 3 perspective, this link is like an ethernet link. The remote router will remove the outer packet, and continue forwarding the inner packet as usual.Ī GRE tunnel is a logical interface on a router. The outer IP packet, instead, delivers the whole thing to the remote router. The internal IP packet will be the original one, of course. Every time a router decides than an IP packet should go into a GRE tunnel, it takes the whole packet and put it inside another IP packet. Using the GRE protocol, you can create virtual links between routers, that allows them to be directly connected, even if they physically aren’t. GRE stands for Generic Routing Encapsulation, and it is an extremely simple form of tunneling. The tunnel must use the 192.168.1.0/30 addressing plan, with R1 having the lowest address. While doing so, we can only use static routes and no dynamic protocol. We will also need to take care of the routes that instruct the routers on how to use the tunnel. This tunnel shouldn’t be encrypted and should use the standard GRE encapsulation. Our requirement is clear: we need to establish a tunnel to allow communication between the two LANs. However, the two LANs on the routers have private addresses, and can’t communicate with each other. The topology is quite simple: all routers are lined up in a row, and R1 can already communicate with R2 using the public addresses. You can download it for free with the link below.
Since we are going to use some new configuration commands, we have created a Packet Tracer lab. This article teaches you how to configure a GRE tunnel between two routers. In this article, we will see how to do it. With a GRE Tunnel (Generic Routing Encapsulation), you can emulate a private network while having only Internet links. What if the server should be internal? In many cases, you want all the remote sites to access the servers in your main site, but don’t want anyone else to access them. If the server should be public, you might want to use NAT. If you have a server with a private IP address, you can’t just expose it to the Internet. However, it has a major flaw: it works with public addresses only. The Internet is fast, cheap, and world-wide available, unlike many private WAN technologies. Whether you have a few branches, or plan connecting home workers, you may end up using the Internet. Any growing business is likely to have multiple sites.
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