Classless and Classful Routing

So far this chapter has reviewed the basic forwarding process for IP packets in a Cisco router. The logic requires matching the packet destination with the routing table, or with the CEF FIB if CEF is enabled, or with other tables for the other options Cisco uses for route table lookup. (Those options include fast switching in routers and NetFlow switching in multilayer switches, both of which populate an optimized forwarding table based on flows, but not on the contents of t..

Link-State Concepts

Recall that link-state protocols are based on neighbor relationships, so every router within an area knows about all the active links within its area and knows the identity of router-originating information about these active links.   Every router advertises the cost and state of its links. This state information is then propagated one hop away. This propagation of information results in all routers having identical databases. Every router is identified by its uni..

Problems with Unicast and Broadcast Methods

Why not use unicast or broadcast methods to send a message from one source to many destinations? Figure 19-1 shows a video server as a source of a video application and the video data that needs to be delivered to a group of receivers—H2, H3, and H4—two hops away across a WAN link. Figure 19-1 Unicast   The unicast method requires that the video application send one copy of each packet to every group member’s unicast address. To support full-motion, full-screen vi..

Overview of the BGP as MPLS Control Plane

MPLS architecture allows multiple protocols for distributing label information between LSRs.[1] MPLS label-distribution protocols are based on either extending the capabilities of existing protocols, as in the case of BGP and RSVP-TE, or explicitly defining new protocols for this purpose, as in the case of LDP. This chapter mainly focuses on the role of BGP as a label-distribution protocol. BGP and MPLS Interrelationship As discussed earlier, MPLS-based L3VPNs use LDP or RS..

MPLS Forwarding Architecture

You have seen earlier that to make forwarding decisions, edge LSRs consult not only LFIB but also FIB tables. Although the label-based forwarding procedure is simple and conducive for high-performance forwarding, nevertheless edge LSRs still must perform conventional IP address lookups during label-imposition and sometimes during label-disposition operations. If you consider an LSR that is to act as a transit LSR for all traffic, in theory the LSR should be able to forward al..