The BGP topology table, also called the BGP Routing Information Base (RIB), holds the network layer reachability information (NLRI) learned by BGP, as well as the associated PAs. An NLRI is simply an IP prefix and prefix length. This section focuses on the process of how BGP injects NLRI into a router’s BGP table, followed by how routers advertise their associated PAs and NLRI to neighbors. NOTE Technically, BGP does not advertise routes; rather, it advertises PAs plus a..
Distribution routers consolidate connections from access routers. They are often arranged in a configuration that is resilient to failure of a single core router. Distribution routers usually contain topological information about their own region, but they forward packets to a backbone router for inter-region routing. NOTE In smaller regions, distribution and backbone routers may be one and the same. In larger regions, distribution routers themselves may form a hierarchy...
The first version sends all packets destined to the single host 10.35.15.5 out through the Ethernet0 interface. In this case, the router will need to figure out which device on this segment to forward the packet to, because it must put the MAC address of the next hop router in the Layer 2 frame header. The standard mechanism for associating IP addresses with MAC addresses is the Address Resolution Protocol (ARP). The router will send out an ARP request onto the Ethernet segme..
Associating the Frame Relay Map Class
After setting up a Frame Relay map class with the default or user-defined traffic shaping parameters, the configured map class has to be associated with a main interface or a subinterface or assigned directly to a VC. For this purpose, the frame-relay class interface configuration command is used to associate a created Frame Relay map class with a specified main interface or subinterface. A user can choose from three levels of a hierarchy when associating a Frame Relay map ..
Routing Over Multiple Paths with Equal Costs
In large, highly redundant networks, it is common to have many possible paths between two points. By default, the router will install up to four routes to the same destination in the routing table for most routing protocols, provided that all of these routes have the same cost. But sometimes this is either too many or too few, so these commands offer a way to change the defaults. For BGP, the default value is one path because of the sheer number of routes in the public Intern..
