Multicast Protocol Overview

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.

Shawn Moore invites you to follow my study progress at http://shawnmoorecisco.blogspot.com/. I also invite you to download my free CCNA eBook lab book at: http://www.configurethenetwork.com.

Article Source: http://EzineArticles.com/?expert=Shawn_Moore

EIGRP Challenge Lab

I did my best to get through all of the tasks for the EIGRP Challenge Lab but I was unable to complete two tasks because I wasn't sure what they we really wanting me to do. The first was to filter a specific network from advertising out of a routers interface. The other task was to filter a network from entering a routers interface. I wasn't sure if I was just supposed summarize the network or create access-lists, route-maps, etc to deny the traffic. Besides that I managed to finish every other task successfully.

I had to change EIGRP settings such as manual summarization, change hello timers, and implement MD5 authentication which was all pretty straight forward. The weirdest task preventing EIGRP from sending multicast updates between the neighbors R1 and R2 (As shown above). I think I figured it out by entering the following command under my EIGRP AS 1

Router 1
router eigrp 1
neighbor 172.16.12.2 s0/0

Router2
router eigrp 1
neighbor 172.16.12.1 s0/0

If any one has any better suggestions on how to limit multicast addresses or if my method was completely wrong, please let me know haha!

A Few Different CCNA Lab Simulation Options

As all of us Cisco certified and future Cisco certified professionals know, the key to passing the CCNA is knowing your hands on configuration like the back of your hand. This presents a challenge to many of us who's budget is limited from buying the latest and greatest Cisco equipment that could cost anywhere from hundreds to thousands of dollars to create a decent lab!

Fortunately many simulation programs are out there to help replicate the hardware and software needed to pass the exam. Even newer to the Cisco world and in my opinion closer to the real thing is emulation software that uses the actual IOS to simulate working on a Cisco router.

Simulation programs provide a very affordable way to create labs to possibly pass the CCNA exam with the bare minimum requirements. There are many simulation programs to choose from. In particular you would want to look for something that has many different Cisco devices to play with along with being updates with the newest IOS commands.

This is something you should note because it's not uncommon for different IOS versions to use a slightly different set of commands to accomplish the same task. Before choosing a simulation program it is also valuable to note that you won't have access to every feature available with a real router and equipment so many commands will not be available to you.

There's also the option of using emulation software such as GNS3 which allows you to completely emulate a Cisco device without the actual hardware. You can also do cool things such as connect to a real Cisco device from the emulator program to help cut down on cost if you already have a few Cisco devices but not enough to create a full CCNA lab. There are a few downsides though as well. The main downside is that as of today, you aren't able to emulate Cisco Switches due to the way Cisco switch hardware works.

However emulators such as GNS3 has a simple Ethernet switch built in that you could use or you can connect your emulated network to an outside world to connect to your Cisco switches. The other downside is that you must have access to actual IOS images in order to use any of the emulator device. This can be particular hard to acquire unless you are a vendor or a CCIE with credentials to access these images from Cisco directly. There are many choices out there but always remember that nothing beats actual equipment and hardware!

Check Out My CCNA Lab Book At: http://www.configurethenetwork.com That Features Over 15 Scenario Based Real World Labs!

Article Source: http://EzineArticles.com/?expert=Shawn_Moore

EIGRP Configured on a Frame Relay Network

I spent a little time this afternoon going over the next EIGRP lab in the CCNP Lab Portfolio. I learned some useful types regarding EIGRP and how it works over Frame. For the most part you can configure EIGRP as normal but EIGRP works off of split-horizon rules. Split horizon pretty much tells a router not advertise a route out of the same interface that it learned the route from to begin with. There for in the diagram router West and East didn't know about each other due to not being able to advertise the same route back to HQ. To get past this, I had to turn of split horizon on the HQ router with the following command:

no ip split-horizon eigrp 1

Once I entered this command under the EIGRP configuration, sure enough all routes came right up!

EIGRP Configuration, Bandwidth, and Adjacencies

I was able to tackle the second lab in the BSCI Lab Portfolio and I can already say with confidence that this book will help me greatly with my studies. I learned a few things between this lab and he first lab that I wouldn't of ever known or thought about. Last week was a very simple two router lab with basic static route configuration. However I learned something that I didn't even know these Cisco routers could do, and that's programming scripts. The Lab Portfolio goes over a neat little script that allows you to test ping configurations without having to go through and ping every interface over and over on each router to verify connectivity. Check out a preview of the script I used for the first lab below, it's called TCL Script and you can access it by typing the tclsh command when you are in enabled mode:

foreach address { 10.1.1.1 10.1.2.1 10.1.3.1 10.1.4.1 10.100.12.1 10.2.1.1 10.2.2.1 10.2.3.1 10.2.4.1 10.100.12.2 } { ping $address }

It pretty much says for each IP address listed, ping it, as simple as that!


I finished my first EIGRP lab today and picked up some cool new commands such as the ping ip address repeat number of times command. Which you can ping an IP address as many times as needed, an example would be ping 10.1.1.1 repeat 1000. This tells the router to ping 10.1.1.1 1000 times, great for testing experiments with routing protocols while packets are being sent across the network!.

Check Out My FREE CCNA Lab Book Available At

www.configurethenetwork.com

Route Reflectors For BGP

BGP specifies that routes learned using Interior BGP should never be learned by other IBGP peers. Because of this rule, BGP requires that all IBGP networks to be complety fully meshed as shown in the picture above. Therefore if you had just 13 routers in your AS running IBGP, you would need 78 total connections in order for all 13 routers to connect to every other router! This causes a big problem with bandwidth due to sending redundant data across all of the routers at the same time.

To over come this, the creation of Route Reflectors (RR) were created. Route Reflectors allows an AS that's running IBGP to not have to use a complete full-mesh topology. Instead you can creat whats called clusters which can group sets of routers together. You can think of a cluster as a mini network that sits inside of your AS. But instead of a full-meshed topology, the cluster is designed in a hub and spoke fashion with one router being designated the Route Reflector (Hub) and the other routers being the spokes that connect to the RR. The Route Reflector then passes its updates to the AS, other clusters, or even other AS's depending on the configuration. This saves on the number of BGP TCP sessions that must be maintained and and also reduces the BGP routing traffic!

Check Out My FREE CCNA Lab Book Available At

www.configurethenetwork.com

BGP Communities

If we used just prefix-lists and distribute lists to filter BGP updates it would be a very manual intensive job due to the size of most BGP networks and the fact that you would have to configure each router one at a time! Today I learned that you can group routers running BGP into groups that can share the same filtering information. Therefore you would only need to configure one of the routers in the group for all of the other routers to know what updates should be filtered and what shouldn't.

"BGP communities function allows routers to tag routes with an indicator (the community) and allows other routers to make decisions (filter) based on that tag. BGP communities are used for destinations (routes) that share some common properties and that, therefore, share common policies; routers, therefore, act on the community, rather than on individual routes. Communities are not restricted to one network or autonomous system, and they have no physical boundaries."

the community attribute is considered an optional transitive attribute. If a router receives an update with community attribute information but doesn't use that attribute, it will ignore it but pass it along to other BGP neighbor peers. The community attribute consists of 32-bits, 16 for the Autonomous System number (AS) and the other 16 identifies the community number.

Don't Forget To Check Out My CCNA Lab Book Available At

www.configurethenetwork.com
This Is The LAST Day That It's Going To Available For The $9.95 Price!