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.

iBGP

Scaling the iBGP mesh

• Two methods:

BGP Confederations 

BGP Route Reflectors

BGP Confederations

• Method to subdivide a single AS into multiple, internal sub-AS’s, yet still advertise a single AS to external peers
• Reduces iBGP mesh

BGP Confederation

• AS10
• AS20
• AS30
• AS300

BGP Route Reflectors (RR)

• Another method to reduce iBGP mesh
• iBGP re-advertisement restrictions are relaxed
• Single iBGP peer advertises (reflects) routes to subordinate iBGP peers
• Clients must not peer with RR’s outside of cluster

Route Reflectors

• (RR)
• AS300
• (RR)
• (RR)

Asymmetric Routing Paradigm

• In the Internet, it is impossible to control end-to-end routing and paths traversed
• Packets may not always traverse same downstream path as they do when forwarded upstream

Asymmetric Routing

Achieving stability

• Using loopbacks
• BGP/IGP Interaction
• Peer groups
• Route-flap dampening
• BGP soft reconfiguration

Stable iBGP Peering

• Peer with loop-back addresses
• iBGP session is not dependent on a single interface
• Loop-back interface does not go down

Peering to Loop-Back Address