Designated Router Optimization on LANs
Figure 10-2 depicts the DR flooding optimization that occurs with sending DD packets over a LAN. Figure 10-2 DR Optimization on a LAN Routers that are not the DR (including the BDR) send DDs to the DR by sending them to multicast address 224.0.0.6, the All OSPF DR Routers multicast address. The DR then acknowledges the DDs with a unicast DD (Step 2 in Figure 10-2). The DR then floods a new DD packet to all OSPF routers (multicast address 224.0.0.5). Figure 10-2 shows..
Classful Distance-Vector to Link-State Protocol
For the sake of this discussion, imagine you are migrating from IGRP, which is the classful distance-vector protocol, to a link-state protocol, OSPF. Remember that both OSPF and IS-IS require hierarchy. The network in Figure 12-2 shows that no hierarchy exists in the network in question, so you must change not only the network protocol, but also the physical circuit to accommodate the hierarchical structure. Figure 12-2. Non-Hierarchical Network Architecture While at..
GP/MPLS Graceful Restart Operation
This section describes the operation of the BGP with an MPLS graceful restart mechanism using the network shown in Figure 7-11. The following discussion assumes that LSR1 and LSR2 are capable of both BGP with MPLS graceful restart and NSF. The following sequence of steps does not necessarily indicate the processing steps of a specific implementation. This description is intended to provide a functional view. • During BGP session establishment, LSR1 and LS..
After an STP topology has converged and becomes loop free, switch ports are assigned the following roles: ■ Root port—The one port on a switch that is closest (with the lowest root path cost) to the root bridge. ■ Designated port—The port on a LAN segment that is closest to the root. This port relays, or transmits, BPDUs down the tree. ■ Blocking port—Ports that are neither root nor designated ports. ■ Alternate port—Ports that are candidate root ports (they a..
Adjusting Local Preference Values
When BGP routers within an AS exchange information about a particular route using iBGP, they include the Local Preference value. All of the routers in the AS are then able to use this value to decide how to weight this route versus other BGP routes to the same destination. BGP consults the Local Preference value early in the route selection process, before even the AS Path attribute. So this provides an extremely useful and flexible way of forcing particular routes to use par..
