Classification Using Class Maps
MQC-based tools classify packets using the match subcommand inside an MQC class map. The following list details the rules surrounding how class maps work for matching and classifying packets: ■ The match command has many options for matching packets, including QoS fields, ACLs, and MAC addresses. (See Table 14-10 in the “Foundation Summary” section for a reference.) ■ Class-map names are case sensitive. ■ The match protocol command means that IOS uses Network B..
When a device realizes that a packet cannot be delivered to its destination, the device sends an ICMP Unreachable message. To help determine the root cause of why the packet cannot be delivered, the ICMP Unreachable message includes one of five code field values to convey the reason for the failure. For instance, in Figure 5-1, assume that Fred is trying to connect to the web server, called Web. Table 5-3, following the figure, lists the key ICMP Unreachable message codes, al..
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..
RFC 1973 and Cisco Implementation of PPP over Frame Relay
RFC 1661 defines the standard PPP specifications, whereas a separate RFC document, RFC 1973, describes a standard method for transporting PPP over a Frame Relay VC connection. Cisco's implementation of the PPP over Frame Relay feature is based on the RFC 1973 specifications. A Cisco router supporting the PPP over Frame Relay feature is able to establish an end-to-end PPP session over an active Frame Relay PVC. NOTE Note that Cisco's implementation of RFC 1973 to suppor..
The Origins of Frame Relay: X.25
v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} Frame Relay has its roots in the X.25 protocol, a robust packet-switched WAN protocol widely deployed in the early 1970s to connect geographically dispersed LANs and WANs. The X.25 protocol works well on noisy transmission mediums, which observe a high rate of errors and packet drops. X.25's windowing, flow, and error control fe..
