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..

Independent Forwarding and Control

With conventional IP packet forwarding, any change in the information that controls the forwarding of packets is communicated to all devices within the routing domain. This change always involves a period of convergence within the forwarding algorithm. A mechanism that can change how a packet is forwarded, without affecting other devices within the network, certainly is desirable. To implement such a mechanism, forwarding devices (routers) should not rely on IP header infor..

CB Marking of CoS and DSCP

Example 14-4 shows how a router might be configured for CB Marking when an attached LAN switch is performing QoS based on CoS. In this case, R3 looks at frames coming in its fa0/0 interface, marking the DSCP values based on the incoming CoS settings. Additionally, R3 looks at the DSCP settings for packets exiting its fa0/0 interface toward the switch, setting the CoS values in the 802.1Q header. The actual values used on R3’s fa0/0 interface for classification and markin..

Segmenting LANs with Switches

So far, this chapter reviewed three legacy internetworking devices. These devices interconnected networks and segments together. During the early 1990s, a bridge derivative found a place in the market. Kalpana introduced a LAN switching device, called the EtherSwitch. EtherSwitch was a glorified bridge in that it offered many ports to attach directly to devices rather than to segments. Each port defined a separate collision domain providing maximum media bandwidth for the att..

Enabling and Disabling NTP Per Interface

Depending on the level of access control required, you can use the ntp disable command to prevent the router from providing NTP services on a particular interface: Router#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router(config)#interface Serial0/1 Router(config-if)#ntp disable Router(config-if)#end Router# You can also prevent the router from providing NTP services on an individual interface with access control lists: Router#con..