Caching Technique Case Study

In previous sections about Cisco switching techniques, we discussed how fast switching is performed, how cache is created from the routing table, and what information is kept in cache. You might be wondering how the cache is populated. During the case study, the text discusses what happens when a packet that must be fast-switched reaches the router.   The cache is built from the routing table. In the scheme prior to CEF, the routing table is built when the routing..

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..

Adjusting EIGRP Metrics

You can use the offset-list configuration command to modify the metrics of routes that EIGRP learns through a particular interface: Router1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z.Router1(config)#access-list 22 permit 192.168.30.0Router1(config)#router eigrp 55Router1(config-router)#offset-list 22 in 10000 Serial0.1Router1(config-router)#exitRouter1(config)#endRouter1# This command can also modify the EIGRP metrics of routes as the..

Configuring a DHCP Database Client

You can ensure your DHCP address assignments are not lost when a router reloads by configuring the router to periodically copy its DHCP database to a remote server. The first example configures a router to use FTP to copy the DHCP database to a remote server: Router1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#ip dhcp database ftp://dhcp:bindsave@172.25.1.1/dhcp-leases Router1(config)#end Router1# The second ex..

Analyzing ACL Log Entries

The Perl script in Example 19-1 parses a router syslog file and builds a detailed report of packets that were denied by logging ACLs. By default, the script will parse every ACL log message that it finds in the syslog file on a server. You can also look for messages associated with a particular ACL by specifying the ACL number or name as a command-line argument. Example 19-1. logscan.pl #!/usr/local/bin/perl##       logscan.pl -- a scrip..