The BGP decision process uses some of the PAs listed in Table 13-7, as well as several others. This section focuses on the decision process as an end to itself, with only brief explanations of new features or PAs. Following that, the text explains the details of some of the PAs that have not yet been covered in the book, as well as some other details that affect the BGP decision process. When a BGP router learns multiple routes to the same NLRI, it must choose a single best r..
Multicast Layer 3 Switching Cache
This section describes how the PFC and the DFCs maintain Layer 3 switching information in hardware tables. The PFC and DFC populate the (S,G) or (*,G) flows in the hardware FIB table with the appropriate masks; for example, (S/32, G/32) and (*/0, G/32). The RPF interface and the adjacency pointer information is also stored in each entry. The adjacency table contains the rewrite and a pointer to the replication entries. If a flow matches a FIB entry, the RPF check compares the..
Proprietary and Open Protocols
The important aspects of routing protocols are that they are fast and that they are classless. Three routing protocols fit that description: OSPF, IS-IS, and EIGRP. All three protocols are wholly acceptable; however, there are some small differences between them from a support perspective. OSPF and IS-IS are public standards, and are therefore supported on a wider variety of equipment than proprietary protocols. This protects against incompatibilities with legacy equipment ..
VTP Pruning: Advanced Traffic Management
A transparent bridge handles LAN frames by filtering (dropping), forwarding, or flooding. Flooding occurs whenever the bridge receives a frame with a destination MAC address for which it has no entry in its bridging table. This happens whenever the bridge never hears from the destination and, therefore, has no entry in the bridge table. Or, no entry can exist because the bridge's aging timer expired for the MAC address. Frames in these scenarios are unknown unicast. Bridges a..
The Cisco proprietary Enhanced Interior Gateway Routing Protocol (EIGRP) is considered to be a balanced hybrid routing protocol (or an advanced distance-vector routing protocol). Specifically, EIGRP advertises routes to directly attached neighbors, like a distancevector routing protocol, while using a series of tables, similar to a link-state routing protocol. EIGRP also offers the benefit of fast convergence after a link failure. Load balancing is supported over both ..
