Cisco

What is a VPN?

A Virtual Private Network or VPN is a network implemented using a shared network infrastructure but so as to provide the security and privacy of a private leased-line network. Older examples would be Frame Relay and ATM. Lately, VPN has come to more often refer to IPSec tunnels over the Internet, or perhaps PPTP or L2TP dial VPN connectivity across a shared internetwork.

For our purposes in this article, the VPNs will be IP networks where the WAN core of a corporate network has been outsourced to a Service Provider. The IP VPN connectivity is provided across a shared IP network belonging to the Service Provider. It will turn out the BGP and MPLS-based VPNs we will talk about are powerful enough to provide secure connectivity (and relatively simple configuration) for both intranets and extranets.

What is SMDS?

Switched Multimegabit Data Service (SMDS) is a high-speed, connectionless, low-delay, packet switched, networking service that operates over public data networks. Think Frame Relay on steroids.

Bellcore developed the specifications for SMDS due to the demand for wide-area networking with LAN-like characteristics. (Pete comment: And some of us think it was a way to experiment with pre-ATM ATM-like data transport, anticipating an ISDN-like 15-year rollout of ATM).

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.