na- tion system. Very large private IP networks can also use BGP. Chapter 8 The Internet and IP Infrastructures Although most Internet users do not use BGP directly, most ISPs must use BGP to enable routing with each other, and it is considered one of the most important protocols of the Internet. BGP is as important to the Internet as SS7 is to inter- provider core call setup on the PSTN (which is discussed in Chapter 4). Like OSPF and IS-IS, BGP is also being updated with new extensions. Current working areas include Multiprotocol BGP, which includes support for IPv6, virtual private networks (VPNs), and multicast addresses. Another working area is Grace- ful Restart, in which data traffic continues to be routed between the restarting router and peers. BGP is also being updated to support Layer 2 VPN and Layer VPN autodiscovery as well as Virtual Private LAN Services (VPLS) signaling. (VPNs and VPLS are discussed in detail in Chapter 9.) Network Access Protocols Network access protocols operate at Layer 2. They provide the underlying basis for the transport of IP datagrams. The original network access protocol was Ethernet, but IP can be transported transparently over any underlying network, including Token Ring, FDDI, Fibre Channel, wireless, X.25, ISDN, Frame Relay, or ATM. Both Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP) were designed specifically for IP over point-to-point connections. PPP provides data link-layer functionality for IP over dialup/dedicated links. In other words, whenever you dial in to your ISP, you negotiate a PPP session, and part of what PPP does is to provide a mechanism to identify and authenticate the user who is dialing up and provide an IP address to the remote computer. Internet Network Architectures Because two key characteristics of TCP/IP are vital to the Internet, it is appropriate to say that the Internet is the TCP protocol suite. First, TCP/IP is a layered struc- ture (refer to Figure 5.9 in Chapter 5, "Data Communications Basics"). It gets more com