Ccna

Introduction

This article continues the series on LAN switching and Cisco Catalyst switches.

MultiLayer Switching (MLS) is a key component of high performance at Layer 3 with the Catalyst 5000 switches. It also is a marvelous opportunity to review what happens when packets pass through a router. Understanding this is very useful in the understanding router and switch performance optimization(s), also in troubleshooting network design and configuration issues.

Prior articles on switching or related topics:

Introduction

This article continues the series on LAN switching and Cisco Catalyst switches. This article we’ll talk about dynamic VLAN’s, and explain what VQP and VMPS are, as well as how they work and how to configure them.

Prior articles in the series:

• Switching: VLAN’s
• Switching: Trunks and Dynamic Trunking Protocol (DTP)

What are VQP and VMPS

We talked in a prior article about configuring ports to belong to a VLAN. This is the static approach to VLAN’s, where a port is always a member of a specific VLAN. You can also configure a port to dynamically determine what VLAN to belong to. Initially (and fundamentally) this process is tied to the MAC address of the end station on the port. Cisco is in the process of making this much more administrator-friendly (and useful!) by tying it into directory servers — more on that later.

What is a Trunk?

We’ve seen in the previous article that a VLAN is a broadcast domain, a collection of ports or users that we wish to group together within an IP subnet, IPX network. We’ve also seen that VLAN’s work to control broadcast, multicast, unknown destination, and problem frame flooding. Our previous discussion centered on the concept of what a VLAN is, perhaps from the perspective of a single switch.

What is a LAN Switch?

Logically, we really need to start with the question, what is a LAN switch?

A LAN switch is a OSI model Layer 2 device, logically similar to a bridge. We’ll primarily focus on Ethernet (Fast Ethernet, Gigabit Ethernet) switches but much of what we say also applies to Token Ring and FDDI.

As you know, bridges learn where computers are by observing source MAC addresses in LAN frames as they pass through the bridge. After first powering on, a bridge forwards frames on all ports and is pretty much indistinguishable from a hub/repeater (except that it regenerates frames, so it does not count towards the Ethernet cable length limitation or hub/repeater 5-4-3 rule). As the bridge learns which MAC address was sourced on which port, it can then be selective about what port(s) a frame is forwarded to, only forwarding the frame to the port appropriate for the destination MAC address.

Introduction

This article follows up on last month’s article, Configuring SNMP in Cisco Routers. We’ll talk briefly about SNMP and switches, and also about Syslog.

previous article  Configuring SNMP in Cisco Routers

Syslog

Syslog is a UNIX process that handles error and status message logging on behalf of system and other processes (daemons). The Event Viewer subsystem on NT is a direct NT counterpart. And there are also free (and not-so-free) syslog daemons now available for NT. For example, Cisco Resource Manager Essentials  includes a syslog message receiver, and syslog reporting functionality.