Checks Before Becoming BGP Neighbors
Similar to IGPs, BGP checks certain requirements before another router may become a neighbor, reaching the BGP established state. Most of the settings are straightforward; the only tricky part relates to the use of IP addresses. The following list describes the checks that BGP performs when forming neighbor relationships: 1. The router must receive a TCP connection request with a source address that the router finds in a BGP neighbor command. 2. A router’s ASN (on the ro..
As discussed in Chapter 4, "Network Topology and Design," accounting of data traffic is not only important for customer billing, but is a crucial part of traffic engineering. For example, knowing the relative size of flows between routers in the network core can help you calculate the most cost-effective topology and circuit size of the core network. In terms of operation, Netflow switching is similar to the fast-switching cache: The first packet of any fl..
Integrated Services Digital Network (ISDN) is used by telephone companies to carry digitized voice and data over the existing telephone system. ISDN has emerged as one of the leading technologies for telecommuting and remote office connection into the corporate headquarters. On the seven layer model, ISDN operates at the physical, data link, and network layers. ISDN basic rate interface (BRI) provides two barrier channels (commonly referred as B channels). Each of these B ch..
A campus network’s core layer provides connectivity of all distribution-layer devices. The core, sometimes referred to as the backbone, must be capable of switching traffic as efficiently as possible. Core devices, sometimes called campus backbone switches, should have the following attributes: ■ Very high throughput at Layer 3 ■ No costly or unnecessary packet manipulations (access lists, packet filtering) ■ Redundancy and resilience for high availability ■ Advanc..
BGP Internals and Verifying eBGP Neighbors
Similar to OSPF, the BGP neighbor relationship goes through a series of states over time. Although the Finite State Machine (FSM) for BGP neighbor states has many twists and turns, particularly for handling exceptions, retries, and failures, the overall process works as follows: Step 1. A router tries to establish a TCP connection with the IP address listed on a neighbor command, using well-known destination port 179. Step 2. When the three-way TCP connection completes, the..
