Cisco

What is Network Address Translation?

The new Network Address Translation (NAT) functionality in the Cisco routers allows privately addressed networks to connect to public networks such as the Internet. When the privately addressed network (the “inside”) sends a packet through the NAT router, the addresses are converted to legal (registered) IP addresses before being passed to the “outside”.

Many sites have been using pass-through firewall gateways to provide this functionality. Well, it’s now available in your Cisco router!

The acronym RMON stands for Remote Network Monitoring. The RMON MIB documents are SNMP standards documents specifying information that an RMON agent can collect for eventual retrieval by RMON network management software. The probe setup and actual data collection uses SNMP. The RMON agent may be embedded in other network hardware (hub, switch, router), or it may be embedded in dedicated hardware (a probe), or it may run on host computers on network segments.

Last article we discussed route caching, the loopback interface, SNMP configuration, time and NTP, and using syslog to capture router console messages.

This month: converting names to addresses: host table and DNS. Then a couple of words about CDP and passwords. Central control of passwords across multiple routers or NAS’s brings us to XTACACS, with a brief nod to TACACS+. We’ll finish with some random related ideas on things you might want to configure into your Cisco routers.

Route Caching

First, more details concerning interfaces.

If a WAN interface is less than 256K, you may want to add “no ip route-cache” to make more buffers available. When process switching (i.e. using the CPU to make the forwarding decisions), the main memory buffers are used (as opposed to shared memory allocated to an interface, or memory elsewhere in the system).

On fast LAN interfaces in 7000 models with Silicon Switch Processor (SSP), you may wish to add per-protocol commands such as:

What Is Cisco Discovery Protocol?

Cisco Discovery Protocol, also known as CDP, is something Cisco has quietly added to its entire product line. If you haven’t read your release notes carefully, you might not have noticed this feature. It’s quietly there on your links, consuming a very small amount of bandwidth for a pretty good purpose.

The CDP protocol is media and network protocol independent. It works with Cisco bridges and switches. (Review question: what layer must it be operating at?) It provides a mechanism for two neighboring devices to learn about each other, even if they don’t both speak the same network protocol. At the end of this article, we’ll see what that might be useful for.