Internet Routing
How BGP Works
BGP is a path vector protocol used to carry routing information between autonomous systems. The term path vector comes from the fact that BGP routing information carries a sequence of AS numbers that identifies the path of ASs that a network prefix has traversed. The path information associated with the prefix is used to enable loop prevention. BGP uses TCP as its transport protocol (port 179). This ensures that all the transport reliability (such as retransmission) is taken care of by TCP and...
Origins and Recent History of the Internet
The Internet started as an experiment in the late 1960s by the Advanced Research Projects Agency (ARPA, now called DARPA) of the U.S. Department of Defense11. DARPA experimented with the connection of computer networks by giving grants to multiple universities and private companies to get them involved in the research. In December 1969, an experimental network went online with the connection of a four-node network connected via 56 kbps circuits. The new technology proved to be highly successful...
Figure 58 BGP Neighbor Negotiation Finite State Machine
The following list summarizes the key states in the FSM example illustrated in Figure 5-8 1. Idle This is the first stage of the connection. BGP is waiting for a Start event, which is initiated by an operator or the BGP system. An administrator establishing a BGP session through router configuration or resetting an already existing session usually causes a Start event. After the Start event, BGP initializes its resources, resets a ConnectRetry timer, initiates a TCP transport connection, and...
Figure 39 The Growth of Internet Routing Tables
Without any plan of action, the routing table would have grown to about 80,000 routes in 1995. Actual data in early 2000, however, showed that the routing table size was around 76,000 routes. This reduction in growth is due to the IP address allocation scheme discussed in the previous section and to the adoption of CIDR. CIDR was an evolutionary step beyond traditional classful IP addresses namely, Class A, B, and C networks. In CIDR, an IP network is represented by a prefix, which is the IP...
Distance Vector Routing Protocols
Distance vector protocols are sometimes referred to as Bellman-Ford protocols, named after the person who invented the algorithm used for calculating the shortest paths11 and for the people who first described a distributed use of the algorithm11. The term distance vector. is derived from the fact that the protocol includes a vector (list) of distances (hop counts or other metrics) associated with each destination prefix routing message. Distance vector routing protocols, such as Routing...
IP Address Allocation
Class A network numbers are limited resources, and the allocation from this space is restricted. Although Class A space will continue to be distributed, it's now being allocated on a subnetwork basis, rather than in entire classful boundaries. Class B addresses are restricted as well, and are allocated on a subnetwork basis. Class C addresses are usually allocated from the upstream service provider's address space. Table 3-4 summarizes the current allocation of Class C address space. Table 3-4....
Customer Premises Equipment
Customer premises equipment (CPE) usually includes the router, the CSU DSU, the cabling, and often an analog modem for OOB (out-of-band) access for monitoring and management. ISPs typically offer the customer a choice of buying the CPE and access line, buying just the access line, or just paying a monthly fee with all equipment and access needs taken care of by the ISP. As with most everything, any arrangement is available at the right price. ISPs usually are responsible for maintaining...
Route Dampening
Another mechanism for controlling route instability is route dampening. A route that appears and disappears intermittently causes BGP UPDATE and WITHDRAWN messages to be repeatedly propagated on the Internet. The tremendous amount of routing traffic generated can use up all the link's bandwidth and drive up CPU utilization of routers. TIP See the section Route Dampening in Chapter 12. Dampening categorizes routes as well either behaved or ill behaved.
Network Address Translator
Companies migrating from a private address space to a global address space can do so with the help of Network Address Translator (NAT)U technology. NAT technology lets private networks connect to the Internet without resorting to renumbering IP addresses. A NAT router is placed at the border of a domain it translates the private addresses into global addresses, and vice versa, when internal hosts need to communicate with destinations on the Internet. In Figure 3-20, Hosts A and B have private...
Potential ISP Bottlenecks and Subscription Ratios
The provider's network is only as strong as its weakest link. There are two potential ISP bottlenecks oversubscription of backbone trunks and small tail circuits leading to a POP or downstream customer. A provider should not recklessly oversubscribe its connections. ISPs that attempt to save money by overloading their routers or connections will end up losing credibility in the long run. Oversubscription occurs when the cumulative utilization of multiple links exceeds the bandwidth of the pipe...
Basic IP Subnetting
Basic subnetting and variable-length subnets are often misunderstood. This section gives a brief introduction to how subnetting works, and the next section discusses variable-length subnet masks (VLSMs). A subnet, or subnetwork, is a subset of a Class A, B, or C network. To better understand subnetting, it helps to take a closer look at IP addresses that are not subnetted. As explained earlier, IP addresses are comprised of a network portion and a host portion, representing a static two-level...
TCP MD5 Signature Option
The TCP MD5 Signature Option, defined in RFC 2385 u, is used to help BGP protect itself from spoofed TCP segments and, particularly, TCP resets. The TCP MD5 Signature Option employs MD5's message digest algorithm, defined in RFC 1321 . More details regarding the usefulness of the TCP MD5 Signature Option can be found in the specification. The extension provides a mechanism for TCP to carry a digest message in each TCP segment, where the digest utilizes information known only to the connection...
Example 1134 BGP Table for RTF
BGP table version is 8, local router ID is 192.68.5.1 Status codes s suppressed, d damped, h history, * valid, best, BGP table version is 8, local router ID is 192.68.5.1 Status codes s suppressed, d damped, h history, * valid, best, Network 192.68.11.0 24 is learned via IBGP (note the i at the far right) with NEXT_HOP 172.16.20.1, which is the IP address of RTA's external neighbor. The EBGP NEXT_HOP IP address is usually preserved inside the routing domain, which is why it is very important to...
Relation to Traffic Routing
The following are the major tasks of the RA per the NSF proposal Promote Internet routing stability and manageability. The route server accomplishes much of this task by reducing the number of BGP peers a router is required to maintain and by applying policy before passing routing information on to the peer, thereby alleviating the processing resources required by the router to filter the routing information. Establish and maintain network topology databases by such means as exchanging routing...
The Internet Today
The decommissioning of the NSFNET had to be done in specific stages to ensure continuous connectivity to institutions and government agencies that used to be connected to the regional networks. Today's Internet infrastructure is a move from a core network (NSFNET) to a more distributed architecture operated by commercial providers such as UUNET, Qwest, Sprint, and thousands of others, connected via major network exchange points, as well as direct network interconnections. Figure 14 illustrates...
What Is a NAP
In NSF terms, a NAP is a high-speed switch or network of switches to which a number of routers can be connected for the purpose of traffic exchange. NAPs must operate at speeds of at least 100 Mbps and must be able to be upgraded as required by demand and usage. The NAP could be as simple as an FDDI switch (100 Mbps) or an ATM switch (usually 45+ Mbps) passing traffic from one provider to another. The concept of the NAP was built on the FIX and the CIX, which were built around FDDI rings with...
The Very High Speed Backbone Network Service
The very high-speed Backbone Network Service (vBNS) project was created to provide a specialized backbone service for the high-performance computing users of the major government-supported SuperComputer Centers (SCCs) and for the research community. On April 24, 1995, MCI and NSF announced the launch of the vBNS. MCI's duties include the following Establish and maintain a 155 Mbps or higher transit network that switches IP and CLNP and connects to all NSFNET-funded NAPs. Establish a set of...
Transitioning the Regional Networks from the NSFNET
As part of the NSFNET solicitation for transitioning to the new Internet architecture, NSF requested that the regional networks (also called mid-level networks) start transitioning their connections from the NSFNET backbones to other providers. Regional networks have been a part of the NSFNET since its creation and have played a major role in the network connectivity of the research and education community. Regional network providers (RNPs) connect a broad base of client member organizations...
Black Holes
List of Customers and Corresponding Providers Table 3-6. List of Customers and Corresponding Providers Note that Onenet and Twonet are multihomed to ISP1 and ISP2 with their address ranges taken from ISP1 (see Figure 3-14). Advertising aggregates is a tricky business. Customers and ISPs have to be careful about the IP address ranges that the aggregate covers. No one is allowed to aggregate someone else's routes (proxy aggregation) unless the aggregating party is a supernet of the...