Cisco Certification Topics

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EIGRP associates five different metrics with each route:

K1 = Bandwidth modifier

* Minimum Bandwidth (in kilobits per second)

K2 = Load modifier

* Load (number in range 1 to 255; 255 being saturated)

K3 = Delay modifier

* Total Delay (in 10s of microseconds)

K4 = Reliability modifier

* Reliability (number in range 1 to 255; 255 being the most reliable)

K5 = MTU modifier

* Minimum path Maximum Transmission Unit (MTU) (though not actually used in the calculation)

I also spent time learning about the neighbor table, topology table, and routing tables EIGRP use to determine the best route or Successor route. I spent time going through the 5 types of packets EIGRP uses for making this routing protocol works. Hello's, Updates, Queries, Replies, and ACK (Acknowledgements) are all used in conjunction to make EIGRP work. Today I'm going to be going through many different EIGRP configuration scenarios along with learning more about the DAUL algorithm.

I learned exactly how DUAL works within EIGRP by reading through the CCNP Study Guide along with creating lab scenarios and watching EIGRP debugs. Seeing it in action through the debugs and reading the study-guide book examples gave me a way better understanding of exactly what's going on when the EIGRP AS topology changes. Using the EIGRP Packets it sends EIGRP Queries, Updates, and Replies when the topology changes. I have a fuller understanding of why this protocol is considered a hybrid protocol.Because it does distant-vector tendencies like split-horizon and hold-down timers while it does link-state tendencies such as using the metrics too determine the best path rather than hop count.

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: Configure the Network.

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I started the last chapter of the CCNP Study Guide book today which is about implementing IPv6 (IP Version 6).IPv6 is a technology developed to overcome the limitations of the current standard, IP Version 4 (IPv4). The major shortcoming of IPv4 is its limited amount of address space. With the amount of IP enabled devices growing at a steady rate, many regions throughout the world are seeing a need for more IP addresses. In the United States, the Department of Defense (DoD) is a primary driver for the adoption of IPv6 and has set a date of 2008 for all systems with the US government to be set to this standard.

IPv6 allows for better scalability with networks and supplies what seems like a limitless amount of IP addresses to use. IPv6 provides the following enhancements:

* Larger address space - IPv6 address are 128 bits which is 4 times larger than IPv6's size of 32 bits. IPv4 had approximately 4,200,000,000 possible address while IPv6 has 3.4 x 10(38) possible addresses. The number is so big that it is alot simpler to see it in arithmetic form!
* Simplified header - IPv6 has a simpler header compared to IPv4 which allows for fast processing. IPv6 is designed in a way that check-sums aren't needed to be computed at every node unlike IPv4.
* Support for mobility and security - Mobility and security help ensure compliance with mobile IP and IP security (IPsec) standards. IPv6 provides a standard that allows IP addresses to move across areas without breaking the established connection. IPsec is also enabled by default for all IPv6 devices. IPv4 doesn't provide either mobility or IPsec security options by default.

IPv6 has three main types of addresses that are similar and different from IPv4:

* Unicast - Similar to an IPv4 unicast address, an IPv6 unicast address is for a single interface. Like IPv4, a subnet prefix is associated with each address. The two different types of unicast addresses are global aggregatable and link-local
* Anycast - Is a new address type that is assigned to a set of interfaces on different devices using IPv6. A packet that is sent to an anycast address goes to the closest interface identified by thr anycast address. Therefore all nodes using the same anycast addess should provide the same type of service.
* Multicast - An IPv6 multicast address identifies a set of interfaces on different devices. A packet sent to a multicast address is delivered to all the interfaces that is apart of that multicast group similar to IPv4.

IPv6 doesn't have broadcast address like IPv4 does. Broadcasts are replaced by multicasts and anycasts. Multicast enables efficient network operation by using a number of specific multicast groups to send requests to a limited number of computers on a network. Multicast groups prevent most of the problems that happens with broadcast storms on IPv4.

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: Configure the Network.

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

Today I studied the different BGP Attributes that are used to determine routes. There are Well-Known Attributes and then there are Optional Attributes. Well-Known attributes must be recognized and propagated to BGP neighbors. Optional Attributes may be propagated to neighbors depending on the attributes meaning. Within these two types of attributes, there are sub attributes.

Well-Known Mandatory Attributes (Must be included in BGP Updates): - AS-path - Next hop - Origin

Well-Known Discretionary Attributes (Not mandatory to be included in BGP Updates): - Local preference - Atomic aggregate

Optional Transitive Attributes (Must be passed to other AS's even if attribute isn't used): - Aggregator - Community

Optional Nontransitive Attibutes: (Doesn't have to be passed to other AS's): - Multiexit-discriminator (MED)

I've also reviewed how BGP Synchronization works along with the many BGP message types. Synchronization tells BGP to wait until all routers have the same IGP information before updating other AS's with the info when using redistribution of BGP into IGP. From what I've been reading synchronization is outdated as most BGP updates are to large to be redistributed into IGP's anyways (scalability). BGP message types are used for establishing BGP neighbors along with providing keep-alives and BGP router updates.

Path Vector is like an updated scalable version of distance-vector routing. However it has one main difference than any other distance-vector or IGP. BGP doesn't use broadcasts or multicasting since it uses TCP as it's transport protocol. TCP is used because it's able to send a large amount of data reliably, the BGP table has over 190,000 entries in the full routing table currently! This size would actually be in the millions but thanks to technologies such as CIDR, the table size has been reduced considerably. Since BGP doesn't use any type of broadcasting mechanism, an AS being use to transit BGP routes between other AS's must be fully meshed within the transit AS. In other words every router running BGP in a transit AS must be seen by every other BGP router in that AS. this is becuase the BGP updates are sent as unicast messages which aren't forwarded in a multicast manner i.e. one-to-one messages.

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: Configure the Network.

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

Unlike your typical home router/switch devices, most Cisco business class routers and switches allow device configuration through the Command Line Interface (CLI). But just how do you get to this CLI to implement the network settings you desire? You do so by usually connecting to the device via console, VTY, or sometimes auxiliary (AUX) access.

When connecting by console, the device is physically located next to you and you connect what's called a roll-over cable or more commonly a console cable. you connect one end to your serial port (DB9 Port) on your PC and the other RJ45 port into the console port labeled on your Cisco router or Switch. Once you have physically connected to your device you can then use a terminal emulator such as Hyper terminal or Putty to access the Command Line Interface and communicate with your device.

Most times physical access to a business class Cisco Router or Switch isn't possible so you will usually connect to the CLI via the VTY settings. The Telnet and more commonly used Secure Shell (SSH) is used to remotely connect to a Cisco device. By using the device's IP address, one can access the device using Telnet or SSH from virtually any location. SSH is most often used due to its secure nature when sending information and commands across the vast Internet.

One other way to access a Cisco device is by using the AUX port which provides dial-in access similar to how a modem works. This type of access is particularly useful when the device looses IP connectivity but you still need to access the device to make configuration changes. Usually these configuration changes consists of configuring an alternate route for the device to route packets while it's normal IP route is down for whatever reason (e.i. T1 circuit looses physical connectivity).

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

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