This section demonstrates how metrics can be used by one AS to influence routing decisions of another AS. In Figure 11-8, AS3 is the customer of provider AS1. AS3 wants to generate metrics toward AS1 to influence inbound traffic. In case all BGP attributes are the same, BGP will prefer routes with a lower metric over routes with a higher metric. Figure 11-8. Setting the MED Attribute RTA and RTF are running IBGP internally and EBGP with the provider AS1. RTG is an int..
Like many other protocols that perform error recovery, TCP uses a sliding window mechanism to perform flow control. The mechanics are probably familiar to most readers—the receiver states a window size, in bytes, using the Window field of its TCP segments sent over the TCP connection. This window is sometimes called the receiver’s window, the receiver’s advertised window, or the granted window. The sender can then send only one window’s worth of data to the receiver w..
Standards Bodies and Incident Response Teams
Numerous standards bodies today help a network administrator design a sound security policy. The two main entities that are helpful are the Computer Emergency Response Team Coordination Center (CERT/CC) and the various newsgroups that enable you to share valuable security information with other network administrators. CERT/CC is a U.S. federally-funded research and development center at Carnegie Mellon University in Pittsburgh, Pennsylvania. Following the infamous worm incid..
Using BPDU Filtering to Disable STP on a Port
Ordinarily, STP operates on all switch ports in an effort to eliminate bridging loops before they can form. BPDUs are sent on all switch ports—even ports where PortFast has been enabled. BPDUs also can be received and processed if any are sent by neighboring switches. You always should allow STP to run on a switch to prevent loops. However, in special cases when you need to prevent BPDUs from being sent or processed on one or more switch ports, you can use BPDU filte..
OSPF area design requires the use of a backbone area, area 0, with each area connecting to area 0 through an ABR. However, in some cases two backbone areas exist; in other cases, a nonbackbone area may not have a convenient point of connection to the backbone area, for example: Case 1. An existing internetwork needs to add a new area, with a convenient, low-cost connection point with another nonbackbone area. However, that connection does not give the new area any conn..
