| 4.1 | Suppose that host A is multihomed, with one interface accessible to the Internet and the other interface on an enterprise's home network. Suppose further that host A is configured to forward IP packets from one interface to the other. In terms of a remote user wishing to access the home network, what advantages do PPTP and L2TP have over the remote user merely connecting to host A over the Internet using SSH, Telnet, or a similar protocol? |
| 4.2 | Why does L2TP need a random vector when encrypting hidden AVPs? |
| 4.3 | We said that MPLS tunnels IP datagrams or some other network-layer protocol. Explain how MPLS meets the definition of tunnel that we gave at the beginning of this chapter. |
| 4.4 | How do the interface protocols, such as Ethernet, know that an MPLS label is present? This is obviously important, as an Ethernet, say, frame will be demultiplexed differently if an MPLS label is present. |
| 4.5 | Use gtunnel to build a GRE tunnel between two hosts. |
| 4.6 | Suppose that we have two gtunnel-based IP-in-IP tunnels to a host H. Our ipip program uses raw sockets, so each instance of the program will receive a copy of every IP datagram sent to either tunnel. Modify ipip to account for this. |
| 4.7 | Add soft-state functionality, as discussed in Section 4.2, to the ipip program. |
