A few days ago I posted some of my thoughts about the lack of entry/mid-level bloggers out there. Although not overwhelming, the response was rather positive and results were unexpected. What’s unexpected? I didn’t expect anyone to actually reply much less, introduce their own blog. Well I’m glad they did. We certainly need to see more of this.

Here are some of the new CCNA/CCNP blogs to note:

• Cisco Fun – This from a guy who calls himsef Suffah. He’s currently studying for his CCNP. A regular poster on the techexams.net forums. Interestingly, we both passed our CCNA exam on the exact same day. Will we repeat the same feat (hey that rhymes!) for BSCI? We shall see…
• Network Bit – An engineer by the name Joey Boyer. He just recently started a new CCNP blog and will be joining us in the same journey. He is actually still working on Security+, but soon plans to move on to CCIP on his way to CCIE
• CCNP2B – Another budding engineer by the name of Michael Hocutt currently working on BSCI. His goal is to endure the fun and exciting journey through CCNP and beyond.
• CCNP Adventure – “I have started this blog as a direct response to a call from popular CCNP Blogger, Aragoen Celtdra” is the first sentence on his first post. I didn’t realize I was popular . Nevertheless, let’s encourage him to continue posting and help each other out on our quest.

These are just some of the few new ones. Let’s also not forget some of the CCNA/CCNP bloggers that have been out there for a while.

• Network Ninja – Here, Deon Botha, our brotha’ from another motha’… and fatha’ , who hails from South Africa blogging about his journey towards attaining his CCNP. He passed CCNA in March 2008 and has already made a mark in the blogging world with his excellent write ups and lab tutorials. He works for a Cisco Partner in South Africa as a Solutions Manager. He hopes to ultimately attain his R&S CCIE.
• CCNP Pursuit – A network engineer from Columbus. Ohio. He blogs about his pursuit for the CCNP and hopes to achieve a CCIE. Not much is known from him but he writes a pretty good blog.
• Cisco Black Belt – Currently a cisco white belt, this dude will someday achieve the top level from the Cisco dojo. Just a few weeks away from attaining his CCNA so let’s give him some love and drop some notes of encouragement on his blog.
• Common Abnormality – Currently studying for the ISCW, Jeremy L. Gaddis is no stranger to technology. A self-proclaim technological swiss-army knife, his experience extends from working on high-speed fiber optic networks to occasionally hacking some perl and php scripts to teaching as an adjunct faculty at a post-secondary institution. He also owns his own consulting firm and his favorite color is sushi. huh!
• IT Daddy – A cool guy, blogging about his CCNA experience. I’ve never met this guy but if there ever was a person I’d want watching my back (in case I trip on an ethernet cable in the data center or something ) , it’s this fellow right here. I’ve known him since I started my studies and a frequent poster at techexams forums. A real class act who always checked up on me regularly by sending me flowers (oops), I meant email messages reassuring me that I “gots that baby down!” Check him out in all his craziness.

Lastly I have to mention this blog, that even though it’s owner is no longer with us, is still one of us. He has served to inspire us and show us commitment in what he does through his own accounts:

• Jonathan Kintner

Well there you have it folks. Our list of CCNA/CCNP candidates is growing. And hopefully as this list crosses over to the CCIE list more bloggers and Cisco hopefuls out there join the fray.

By the way if you happened to have contacted me before and I left off your blog, I humbly apologize. I’d like to promote as many of you out there so please let me know if I didn’t catch yours (or if you have a new blog or existing blog focused on Cisco certification) and I’ll surely add yours next. You may go to the about page and fill out the “Contact Me” form. If not I can always steal your links from someone else who has it

Basic Configuration

• The AS number on the router eigrp command must match against other routers.
• The network-number on the network command indicates which networks will be part of the same EIGRP autonomous system.
  • This can either be a network number, a subnet, or a specific address of an interface
  • Determines which links on the router to advertise to and which links to listen advertisements on.
• The wildcard-mask is optional. The wildcard bits 0 means to match the bits, 1 means don’t care.
  • If wildcard mask is not used, EIGRP will include the whole classful network of the configured network-number.
  • To illustrate the point:

• In the above table, because no wildcard mask was used in the original configuration, RouterA changes the network command to show classful networks.
• Following is an example using a wildcard mask:

routerA(config)#router eigrp 109
routerA(config-router)#network 10.1.0.0 0.0.255.255
routerA(config-router)#network 10.4.0.0 0.0.255.255
routerA(config-router)#network 172.16.2.0 0.0.0.255
routerA(config-router)#network 172.16.7.0 0.0.0.255

• The example above matches all four interfaces.

The ip-default network Command

ip default-network network-number

• The network-number is considered the last-resort gateway that will be announced to other routers.
• Before the router (on which this command is configured) announces the candidate default route, that network must be reachable by this router.
• The network number specified in the command must also be passed to other EIGRP routers so that those routers can use this network as their default network and set as their gateway of last resort to this network.
  • meaning the network must be EIGRP-derived network in the routing table, or
  • must be generated with a static route and then redistributed into EIGRP.
• Multiple default networks can be configured.
  • downstream routers then use the EIGRP metric to determine the best default route.

Route Summarization

• EIGRP has autosummarization on by default and therefore summarizes on the major network boundary by default. This can be disabled. EIGRP summary routes allows you to summarize on any bit boundaries within the network as long as a more specific route exists in the routing table.
  • Note: Classful routing protocols (RIPv1 and IGRP) automatically summarize routes on the classful network boundary and do not support summarization on any other bit boundaries. Classless routing protocols support summarization on any bit boundary.
  • Distance vector protocols’ drawback has always been the inability to create summary routes at arbitrary boundaries of the network. EIGRP, although based on a distance vector protocol IGRP, added the functionality to do so.
• When configuring summarization on a router’s interface, a summary route is added to the routing table and next hop interface is set to null0 (a directly connected, logical interface)
  • This is to prevent loops by preventing the router from forwarding a packet destined to an unknown subnet from being forwarded to other routers. If the destination subnet is unknown but the packet matches the summary route, the packet is forwarded to null0 and subsequently gets dropped (it goes to the bit bucket).
• An effective summarization design is to have contiguous subnets configured on all interfaces of a router.
• The number of subnets that can be represented by a summary route is directly related to the difference in the number of bits between the subnet mask and the summary mask.
  • The formula to calculate the number of subnets that can be represented by a single summary route is [2ⁿ] where n is the difference in the number of bits between the summary and the subnet mask.
  • for example, if the summary mask contains 3 fewer bits than the subnet mask, eight subnets (2³ = 8 ) can be summarized into one advertisement.
• When configuring summary routes, the IP address of the summary route and the summary mask must be specified.

Configure Manual Route Summarization

• As mentioned above, although EIGRP autosummarizes by default, there are cases you may want to turn it off.
  • One such case is if you have a discontiguous network.
• After you turn off the autosummarization, you can then configure a manual summarization and create a summary route on any bit boundary.

• The parameters for the manual summarization configuration are:
  • as-number – the EIGRP autonomous system number
  • address – the summary address. It does not have to be aligned on Class A, B, or C boundaries
  • mask – the subnet mask for the summary address
  • admin-distance – an optional parameter to configure the Administrative distance (0 to 255).

Consider the following example:

• The figure above shows a discontiguous network (172.16.0.0 -> 10.0.00 -> 192.168.4.0.
• Under the default settings, Router1 and Router2 summarizes routes to the classful address 172.16.0.0. As a result, Router3 has 2 equal routes to network 172.16.0.0. If there are packets intended to any specific router, there is a good possibility that the packets will get lost because Router3 sees the routes to either networks as equal and would load balance between the two.
• In order to prevent this, automatic route summarization should be turned off on both Router1 and Router2 as shown below:

Router1(config)#router eigrp 100
Router1(config-router)#network 10.0.0.0
Router1(config-router)#network 172.16.0.0
Router1(config-router)#no auto-summary

Router2(config)#router eigrp 100
Router2(config-router)#network 10.0.0.0
Router2(config-router)#network 172.16.0.0
Router2(config-router)#no auto-summary

• As a result of the above configurations, the networks will not be autosummarized at the major network boundary and all the subnet routes will be carried into Router3′s routing table.
• An EIGRP router autosummarizes routes only for networks to which it is attached to. Because Router3 does not own the 172.16.0.0 network, it will not autosummarize 172.16.1.0 and 172.16.2.0 it learned from Routers 1 and 2. Router 3 will therefore send routing information about 172.16.1.0 and 172.16.2.0 to the world.
• However, a manual summary route can be configured out of Router3′s s0 interface in order to reduce route advertisements about network 172.16.0.0 to the world:

Router3(config)#router eigrp 100
Router3(config-router)#network 10.0.0.0
Router3(config-router)#network 192.168.4.0

Router3(config)#interface s0
Router3(config-if)#ip address 192.168.4.2 255.255.255.0
Router3(config-if)#ip summary-address eigrp 100 172.16.0.0 255.255.0.0

• For manual summarization, the summary is advertised only if a component (a more specific entity that is represent in the summary) of the summary route is present in the routing table.

• Summary routes have an administrative distance of 5. The administrative distance will only show on the local router performing the summarization by using the show ip route network command, where network is the specified summary route.
• Standard EIGRP routes have administrative distance o 90.
• External EIGRP routes have administrative distance of 170.

Resources

1. Configuring EIGRP – Cisco IOS IP Routing Protocols Configuration Guide, Release 12.4
2. Configuring a Gateway of Last Resort Using IP Commands
3. EIGRP – Summarization

This entry is not an authoritative guide. These are merely notes and rehash of the primary text materials and resources that I use. For a thorough guide of the BSCI course, consider purchasing Building Scalable Cisco Internetworks (BSCI) (Authorized Self-Study Guide) (3rd Edition) by Diane Teare and Catherine Paquet, as well as following the links on the resources section of this entry.