I've covered some of the basic elements of Multicasting, such as IGMP and the Layer 2 switching components in my previous posts (Part 2). This article will go into the technology behind Multicasts at Layer 3 and some of the issues limiting wider use of Multicast technology.

As you recall in my first post, I observed that Yahoo's transmissions of live NHL games would seem to be good candidates for Multicast, yet were being sent as unicast. Then I covered the simple issue of enabling Multicast within a local area network. Coming full circle, here we are diving into Multicast technology to understand why it isn't more widespread.

In my last post, I discussed multicasts and some of the basic concepts. This time, I'm going to discuss technologies used by switches and routers to enable and configure multicasts. Specifically, I'm going to dive into addressing and IGMP. Understanding the details behind multicasts helps understand configuring multicasts as well as the issues limiting the use of multicasts on the web.

With the growth of IPTV and other IP media streaming technologies, applications for multicast technology are increasing. Live Video broadcasts and VoIP applications are viable uses for real time transmissions over an IP network from a single source to multiple recipients.

Most data transmissions are unicasts, which are a one-to-one data stream sent from one device to another device. Email, web surfing, and file downloads are all examples of unicasts, even for the busiest sites or most downloaded files. Although a single web page may be visited thousands of times each day, each time it is viewed it is individually transmitted to the requestor's PC as a unicast.

In my last two posts on this subject, I've covered some of the basics and tools used to perform packet captures, highlighting the well known software from Wireshark. In this installment, I'm going to show how I used Wireshark packet captures to solve a real network problem.

Using packet papture software like Wireshark is a useful troubleshooting technique that can be used to examine packets and gather details to help find the root of a problem. In my previous post, I talked a little bit about how to use Wireshark and walked through some steps to run a simple packet capture from a PC. This time, I'm going to go a bit deeper into the how to for doing packet captures.

One of the features I've seen in newer small network routers is the inclusion of a packet sniffer/capture/trace tool within the diagnostic menus of the device. Routers I've recently tested with this functionality include the SonicWall TZ190W, D-Link DFLCPG310, and Netgear's newly released FVX538 and FVS336G.

In each case, these devices have the ability to capture packets on a specific WAN port and/or on the LAN interface. Some of these routers have more sophisticated filtering capabilities than the other, but they all seem to have the same basic functionality of capturing packets.