OSPF Design in Light of LSA Types
OSPF’s main design trade-offs consist of choosing links for particular areas, with the goal of speeding convergence, reducing memory and computing resources, and keeping routing tables small through route summarization. For instance, by using a larger number of areas, and the implied conversion of dense types 1 and 2 LSAs into sparser type 3 LSAs, the OSPF LSDBs can be made smaller. Also, link flaps in one area require SPF calculations only in that area, due to the partial ..
Another distinguishing characteristic of routing protocols is speed. Convergence times aregenerally grouped as slow or fast. Fast convergence means that the routing protocol is ableto recognize a problem and fix it faster than a user can call to report the problem. Slowprotocols, such as RIP and IGRP, can take minutes to converge. Fast protocols, such asOSPF, IS-IS, and EIGRP, generally converge in less than ten seconds. Table 1-7 shows the convergence speeds of the routing ..
Continuing the example from the previous chapters, the fictitious company ABC, Inc., already is correctly classifying and marking all 11 classes of traffic from the QoS Baseline Model within its campus. Such marking is being performed at Layer 3 via DSCP. Furthermore, dual-rate policing is used within the campus so that certain AF classes of traffic can be marked down to a second level of drop preference (for example, AF21 can be marked down to AF22). Additionally, the WAN ag..
Table 6-3 illustrates that there are actually five STP states
After the bridges have classified their ports as Root, Designated, or non-Designated, creating a loop-free topology is straightforward: Root and Designated Ports forward traffic, whereas non-Designated Ports block traffic. Although Forwarding and Blocking are the only two states commonly seen in a stable network, Table 6-3 illustrates that there are actually five STP states. Table 6-3. STP States State Purpose Forwarding Sendin..
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 ..
