Static Configuration of Frame Relay Mapping Information
In Figure 7-3, Router3 already knows how to forward frames to Router4, but the reverse is not true. Router3 uses logic like this: “For packets needing to get to a next-hop router that is in subnet 172.31.124.0/24, send them out the one DLCI on that point-to-point subinterface—DLCI 100.” The packet then goes over that VC to Router1, which in turn routes the packet to Router4. In the admittedly poor design shown in Figure 7-3, however, Router4 cannot use the same kind of..
The TCP intercept and unicast reverse path forwarding features of the IOS enable you to configure some basic security against two types of denial-of-service attacks: TCP SYN flooding and source IP address forgery. A denial-of-service (DoS) attack is one in which a hacker overwhelms a network resource with traffic intended not to harm data, but to utilize enough resources on the network resource so that it cannot perform its intended function. For example, a TCP SYN (synchron..
Frame Relay Headers and Encapsulation
Routers create Frame Relay frames by using different consecutive headers. The first header is the ITU Link Access Procedure for Frame-Mode Bearer Services (LAPF) header. The LAPF header includes all the fields used by Frame Relay switches to deliver frames across the FR cloud, including the DLCI, DE, BECN, and FECN fields. The Frame Relay encapsulation header follows the LAPF header, holding fields that are important only to the DTEs on the ends of a VC. For the encapsulatio..
As discussed in the previous section, Ethernet rules limit the overall distance a network segment extends and the number of stations attached to a cable segment. What do you do if you need to go further or add more devices? Bridges provide a possible solution. When connecting networks as in Figure 2-7, significant differences exist when compared to repeater-connected networks. For example, whenever stations on the same segment transmit to each other in a repeated network, the..
On a multilayer switch, you also can enable Layer 3 functionality for an entire VLAN on the switch. This allows a network address to be assigned to a logical interface—that of the VLAN itself. This is useful when the switch has many ports assigned to a common VLAN, and routing is needed in and out of that VLAN. In Figure 11-2, you can see how an IP address is applied to the switched virtual interface called VLAN 10. Notice that the SVI itself has no physical connection to ..
