Well Known Multicast Addresses

IANA controls the assignment of IP multicast addresses. To preserve multicast addresses, IANA is reluctant to assign individual IP multicast addresses to new applications without a good technical justification. However, IANA has assigned individual IP multicast addresses to popular network protocols. IANA has assigned several ranges of multicast IP addresses for specific types of reasons. Those types are as follows KEY Permanent multicast groups, in the range 224.0.0.0-224.0.1.255 POINT...

Advertising BGP Routes to Neighbors

The previous section focused on the tools that BGP can use to inject routes into a local router's BGP table. BGP routers take routes from the local BGP table and advertise a subset of those routes to their BGP neighbors. This section continues focusing on the BGP table because the BGP route advertisement process takes routes from the BGP table and sends them to neighboring routers, where the routes are added to the neighbors' BGP tables. Later, the final major section in the chapter, Building...

Port Fast Uplink Fast and Backbone Fast

Uplinkfast

The Cisco-proprietary PortFast, UplinkFast, and BackboneFast features each solve specific STP problems. Table 3-5 summarizes when each is most useful, and the short version of how they improve convergence time. Table 3-5 PortFast, UplinkFast, and BackboneFast Used on access ports that are not connected to other switches or hubs Immediately puts the port into forwarding state once the port is physically working Used on access layer switches that have multiple uplinks to distribution core...

Time Exceeded ICMP Message

The ICMP Time Exceeded message notifies a host when a packet it sent has been discarded because it was out of time. Packets are not actually timed, but to prevent packets from being forwarded forever when there is a routing loop, each IP packet header includes a Time to Live (TTL) field. Routers decrement TTL by 1 every time they forward a packet if a router happens to decrement TTL of a packet to 0, the router discards the packet and sends an ICMP Time Exceeded message to the sender of the...

IP Addressing and Subnetting Review

First, here's a quick review of some of the core facts about IPv4 addresses that should be fairly familiar to you Written in dotted decimal notation (for example, 1.2.3.4), with each decimal octet representing 8 bits. Addresses are assigned to network interfaces, so computers or routers with multiple interfaces have multiple IP addresses. A computer with an IP address assigned to an interface is an IP host. A group of IP hosts that are not separated from each other by an IP router are in the...