k might not allow this last solution because there might be valid external routes that need to be redistributed. Chapter 11: Redistribution CHAPTER 12 Tunnels A tunnel is a means whereby a local device can communicate with a remote device as if the remote device were local as well. There are many types of tunnels. Virtual Private Networks (VPNs) are tunnels. Generic Routing Encapsulation (GRE) creates tunnels. Secure Shell (SSH) is also a form of tunnel, though different from the other two. Let's take a closer look at these three types: GRE tunnels allow remote networks to appear to be locally connected. GRE offers no encryption, but it does forward broadcasts and multicasts. If you want a routing protocol to establish a neighbor adjacency or exchange routes through a tunnel, you'll probably need to configure GRE. GRE tunnels are often built within VPN tunnels to take advantage of encryption. GRE is described in RFCs 1701 and 2784. VPN tunnels also allow remote networks to appear as if they were locally connec- ted. VPN encrypts all information before sending it across the network, but it will not usually forward multicasts and broadcasts. Consequently, GRE tunnels are often built within VPNs to allow routing protocols to function. VPNs are often used for remote access to secure networks. There are two main types of VPNs: point-to-point and remote access. Point-to-point VPNs offer connectivity between two remote routers, creating a virtual link be- tween them. Remote access VPNs are single-user tunnels between a user and a router, firewall, or VPN concentrator (a specialized VPN-only device). Remote access VPNs usually require VPN client software to be installed on a per- sonal computer. The client communicates with the VPN device to establish a personal virtual link. SSH is a client/server application that allows secure connectivity to servers. In practice, it is usually used just like Telnet. The advantage of SSH over Telnet is that it encrypts all data before sending it. While not originally designed to be a t