DHCP Router Configuration

I spent this morning reviewing DHCP router configuration and the many options that you have as a DHCP server. From what I've seen in real networks most routers won't utilize DHCP configuration unless it's for a smaller network using a Cisco 1841 or something similar. The bigger enterprise routers are usually deployed in bigger environments where there are already dedicated DHCP server(s) in place. I did learn a command that would of helped me tremendously during my CCNA studies.

To all the people studying for the CCNA try out this command on a router and you'll get a nice surprise:

Router# show ip port-map

Yup that's right, you get a complete list of the most common TCP and UDP ports used, very handy for the CCNA exam or just for a quick reference!

IS-iS over Frame Relay

I knocked out the last of the IS IS topics in the CCNP Lab Portfolio finally. One interesting caveat about IS-IS and NBMA (Non-Broadcast Multi Access) networks is that it can only perform as point-to-point connections. Which is very different from OSPF that can use different NBMA technologies such as multi-point. Tomorrow I begin the different routing manipulation topics that's a HUGE part of the exam I hear.

CCNP Portfolio IS-IS Labs

I'm about half way through the CCNP lab portfolio book finally. I started on the first IS-IS lab presented in the book and it refreshed my memory on a lot of the IS-IS topics which I can honestly say that I forgot. The lab was focused on the basics and the end goal was to setup an IS-iS lab where the core network was running as an IS-IS level 2 network. The other goal was to implement security measures to prevent rouge outside networks/routers from trying to create an adjacency to the current IS-IS network which was pretty straight forward. I plan on completing the IS IS portion of this book within the next week or two, I'm working overtime at the NOC this upcoming week so we'll see how far will get by this time next week rolls around!

Finished the OSPF CCNP Portfolio Labs

All of this studying and labs (lots and lots of labs) are starting to pay off. I'm finally starting to grasp many of the CCNP routing topics without having to reference a book or look up how to configure certain commands. I went through the OSPF challenge lab and was able to knock it out in about 20 minutes which is pretty good. One thing about troubleshooting networks is that you can gain a lot of information just from looking at the running configurations and the ip routing table. Looking at the device log (show logging) helps you determine what happened and when, this is very helpful in real world environments. Next up is IS-IS and then the redistribution chapters which is gonna teach me a lot of new techniques I bet!

OSPF Over Frame Relay

Today worked through the CCNP Portfolio lab 3-4 which has to do with OSPF over frame relay. This lab was mostly review for though. I did finally bit the bullet and learn how to setup a Cisco router as a frame-relay switch finally. I always used the frame relay icon in GNS3 for all of my frame relay studies. It was fairly straight forward, just mainly pointing the DLCI's where they need to go and configuring the serial interfaces for frame DCE connections was all that was needed really. I also went through some of the different type of OSPF NBMA topologies you can configure, such as point-to-multipoint or creating neighbor connections through the OSPF configuration.

CCNP OSPF lab Portfolio

I finally finished up the EIGRP section and I'm now moving through some of the OSPF labs. Right now the labs are just going over basics but I have learned a few new things that I never thought about when it came to OSPF. When configuring loopbacks with IP addresses and using OSPF as your routing protocol, If their aren't any specific Router ID's (RID) set, OSPF will use the Loopback address as the RID.

For example if I configured the loopback 1 interface with the IP address 192.168.1.1 255.255.255.0, the router would use this as the RID as well. So when you run the show ip route command, it shows up as 192.168.1.1 /32 instead of the 192.168.1.1 /24 that you have actually configured on the lo1 interface. to circumvent this, you should type in the interface command ip ospf network point-to-point which tells the router to treat the loop back interface as routing destination rather than a routing ID.

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.

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