Multicast Overview

I'm nearing the end of my CCNP Study Guide Book, with only this chapter on multicasting and the last chapter on IPv6 to go. Multicasting enables data to be sent over networks to a group of destinations in the most efficient way. The data is sent from the source as one stream; this single data stream travels through the network. Other network devices only replicate the data through the network if they have other members on their interfaces that are apart of this destination group.

Multicast groups are identified by Class D IP addresses, which are in the range from 224.0.0.0 to 239.255.255.255. Muticast uses the Internet Group Management Protocol (IGMP) and Cisco Group Management Protocol (CGMP) for determining which network devices require the multicast data stream. Protocol Independent Multicast (PIM) is used for determining the best way to route multicast traffic.

There are many differences between Multicast and Unicast packets. Unicast duplicates a packet for each reciever that it needs to send the data too (one copy for each reciver). Multicast sends one packet stream as mentioned previously, downstream routers replicate the packets only on links where receiving hosts exist. Multicast provides the following advantages over unicast:

• Enhanced efficiency
• Optimized Performance
• Support for distributed applications

The disadvantage of multicast is that it uses UDP (User Datagram Protocol) as it's transport protocol. This means that packets are only sent on "best-effort" delivery and that packets aren't sent reliably. In order to cut down on unreliable packets, the multicast applications them selves may need to provide some sort of reliability mechanisms to prevent huge data lost. This could mean more processing power needed on the hosts them selves.

Configure the Network Full CCNA Lab Preview

Hey all, I just wanted to give you a quick snippet of one of the labs that will be available when you purchase the full version of the Configure the Network Lab book. View the picture above for a peek at what Task 8 will have you configuring for your CCNA exam!

Don't forget to download the free CCNA ICND1 Lab book at www.configurethenetwork.com

End of Chapter BGP Labs

The end of chapter 8 consists of 3 BGP labs to test your knowledge of the material you've learned so far. I went through 2 labs today and will complete the last one tomorrow along with the end of chapter questions. The nice thing about setting up and configuring the network examples in the book is that by time you get to the end of chapter labs you will know how to configure everything with ease. I noted today than I configured a total of 75 network labs so far during my BSCI studies the last few months! I'm sure that I'm going to easily pass 100 labs by time I take the exam for the first time, I just want to be as prepped as possible going in.

BGP MED Configuration

When using BGP, sometimes the Autonomous System (AS) wants to influence another AS's routing decision on how incoming packets are routed to its AS. Multiexit-discriminator (MED) is used to configure this setting for BGP peers. Unfortunately MED is one of the last considered processes in the BGP routing process. That means that if local preference is used in the BGP process it can not knowingly override any MED settings you are sending to that remote AS.

Route maps can be used with MED to better load balance settings, using the command default-metric under the BGP configuration will set MED settings. However if two BGP peers in the same AS have different MED values, the lower cost will always be preferred. While the other peer will receive little to almost no routing traffic besides BGP updates. What would be better is creating a route map that specifies which networks should have lower metrics on each BGP peer as shown in the example above.

Multiple AS BGP Lab

I spent this evening creating one of the bigger labs I usually do. My task was to setup a BGP network with 5 AS's in which every AS should be able to reach other loop-free (requirement of BGP anyways). I was also supposed to make Router C choose Router A to send its packets destined for AS 65004. Well I was able to get the BGP network up without to many hitches which is a long way than just a week or two ago. I however could not get my route-map statement for Router A to set the local preference to AS 65004 higher than Router B to work. I'm not sure why but as i finish up this chapter i will review why this command didn't take. I think it might have been the way I applied it to the BGP router configuration (had the route-map set to in instead of out). All in all I would say it was a pretty good success setting up a lab of this size without having to really reference the book for command guidance.

Configure the Network Free Lab Book

Hey everyone, check out www.configurethenetwork.com to download your free ICND 1 lab book today!

BGP Peer Groups

I spent the better part of my morning learning how to configure BGP Peer Groups. Peer Groups provide a way to save router processing time by not having to send an individual update for each IBGP neighbor. If your Autonomous System has a rather large amount of routers (neighbors) running BGP, the processing time each router would have to run could be pretty intensive. Remember that when running IBGP within a transitive AS, all neighbors should be fully-meshed with one another due to the way BGP sends updates (unicast). I was also introduced to distribution lists and how they could be used to tune BGP updates. In the lab I created I used a distribution list to permit internal IP networks from being addressed outside the AS to other AS's.

As you see in the Router A BGP example, the commands to create a peer-group, distribution list, and creating updates for specific networks can be quite extensive compared to other routing protocols.