The selection of a routing protocol is based on the design goals and the physical topology of the network. Both EIGRP and OSPF are recommended as enterprise routing protocols.

When choosing routing protocols, you can use Table 5.3 as a decision table template. Decision tables are discussed in Chapter 2, “Applying a Methodology to Network Design.” Additional rows can be added to specify other parameters that might be important in the specific network.

When to Choose EIGRP

EIGRP is a Cisco-proprietary hybrid protocol that incorporates the best aspects of distance vector and link-state features. EIGRP keeps a topology table, it does not perform periodic route updates, and it does perform triggered updates. It is well suited to almost all environments, including LAN, point-to-point, and NBMA. The EIGRP split-horizon functionality can be disabled in NBMA environments. EIGRP is not suitable for dialup environments because it must maintain its neighbor relationships using periodic hello packets; sending these packets would mean that the dialup connections would have to stay up all the time.

When to Choose OSPF

OSPF is a standards-based link-state protocol that is based on the SPF algorithm for best path calculation. OSPF was initially designed for networks of point-to-point links and was later adapted for operation in LAN and NBMA environments. OSPF can be used on dialup links with the OSPF Demand Circuit feature, which suppresses the Hello protocol. The OSPF hierarchical area requirements impose design constraints in larger networks. One backbone area is required, and all nonbackbone areas must be directly attached to that backbone area. Expansion of the backbone area can cause design issues because the backbone area must remain contiguous.

Border Gateway Protocol

BGP is an EGP that is primarily used to interconnect autonomous systems. BGP is a successor to EGP, the Exterior Gateway Protocol (note the dual use of the EGP acronym). Because EGP is obsolete, BGP is currently the only EGP in use.