Impact of the Decision Process and NEXT_HOP on BGP Updates
The next several examples together show a sequence of events regarding the propagation of network 31.0.0.0/8 by BGP throughout the network of Figure 12-4. R6 originated the routes in the 30s (as in Example 12-4) by redistributing EIGRP routes learned from R9. The purpose of this series of examples is to explain how BGP chooses which routes to include in Updates under various conditions. The first example, Example 12-9, focuses on the commands used to examine what R6 sends to..
The Routing Process Simplified
Until now, this chapter has examined discrete aspects of routing—specifically, peer negotiation and static versus dynamic routing. Before diving into details of routing configuration, it makes sense to pause here and briefly overview the BGP routing process in its entirety. BGP is a fairly simple protocol, which is why it's so flexible. Routes are exchanged between BGP peers via UPDATE messages. BGP routers receive the UPDATE messages, run some policies or filters over the ..
Multipath interference occurs when an RF signal takes different paths when propagating from one wireless station to another. While the signal is en route, walls, chairs, desks, and other items get in the way and cause the signal to bounce in different directions. A portion of the signal might go directly to the destination, and another part might bounce from a chair to the ceiling, and then to the destination. As a result, some of the signal will encounter delay, because it h..
Configuring an Async Serial Interface
Cisco has a class of serial modules that can support either synchronous or asynchronous communications, as required. You can use the physical-layer async command to change the interface from the default synchronous to asynchronous mode: Router3#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router3(config)#interface Serial1/7 Router3(config-if)#physical-layer async Router3(config-if)#encapsulation ppp Router3(config-if)#exit Router3(con..
Restricting TCP Session Direction
You can use the established keyword to restrict which device is allowed to initiate the session. In the following example, we want to allow the client device to telnet to the server, but not the other way around: Router1#configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router1(config)#access-list 148 permit tcp any eq telnet any establishedRouter1(config)#access-list 148 deny ip any any Router1(config)#interface FastEthernet0/0Router1(confi..
