The benefits of route dampening are noticed inside as well as outside an autonomous system. When BGP is redistributed (injected) into an IGP, it is important that BGP instability does not affect internal routing in such a way as to cause a meltdown inside the AS. This is where route dampening can be useful. Routes that are flapping will be suppressed and prevented from being injected into the AS until they show some degree of stability. Figure 10-2 compares the effects of EBG..
Matching AS_PATHs Using AS_PATH Filters
NLRI filtering with AS_PATH filters uses two commands: ip as-path access-list access-list-number {permit | deny} as-regexp neighbor {ip-address | peer-group-name} filter-list access-list-number {in | out} Figure 13-4 shows a sample internetwork used in many of the upcoming examples, two of which show the use of AS_PATH filtering. Figure 13-4 Network Used for AS_PATH Filter Examples Example 13-4 shows an AS_PATH filter in which routes are filtered going from R4 to R3..
In the first section of this appendix you saw the overall MPLS architecture as well as the underlying concepts. This chapter focuses on one particular application: unicast destination-based IP routing in a pure router environment (also called Frame-mode MPLS because the labeled packets are exchanged as frames on Layer 2). This section first focuses on the MPLS data plane, assuming that the labels were somehow agreed upon between the routers. The next section explains the exa..
No discussion of the evolution of data networking would be complete without some commentary on OSI. Benefits of OSI By the early 1980s, the networking community was tired of being tied to proprietary networking solutions. To promote a smoother system with more support, both hosts and networking infrastructure had to come from the same vendor. Admittedly, development according to standards could squash creativity, but from a customer perspective, this was an acce..
Hosts normally use the Address Resolution Protocol (ARP) to resolve an unknown MAC address when the IP address is known. If a MAC address is needed so that a packet can be forwarded at Layer 2, a host broadcasts an ARP request that contains the IP address of the target in question. If any other host is using that IP address, it responds with an ARP reply containing its MAC address. The ARP process works well among trusted and well-behaved users. However, suppose that a..
