Exam #642-801: Building Scalable Cisco Internetworks (Routing) Vendor Cisco Systems Status Live. Available at Pearson Vue and Prometric testing centers worldwide. Reviewer's Rating "You'll need to have a solid grasp of routing protocols and be prepared to face the two or three simulation-based questions you may receive." Test Information 55 to 65 questions, passing score needed is apx. 776 on a scale of 300 to 1,000. Cost: $125 (U.S.). Who Should Take This Exam? Candidates for Cisco's CCNP, CCDP and CCIP. Test Objectives Click here

The main objectives of the Routing exam are implementation and configuration of routing protocols, NAT, LANs and WANs. Since you must hold a valid CCNA to obtain the CCNP, that's where you should start to obtain the fundamental knowledge of distance vector, link state and hybrid routing protocols. The CCNA will also introduce you to NAT and, of course, LANs and WANs. The Routing exam objectives are broken down into three main areas: Implementation and Configuration, Design and Troubleshooting. One of the best online references you'll find on IP routing protocols -- which is about 70 percent of the exam -- is the Cisco documentation found here.

Beyond this information, there are self-study guides and even the official Cisco BCSI course, if you prefer instructor-led training. For self-study I prefer the CCNP Preparation and CCNP Certification Libraries from Cisco Press. There's a lot of overlap between the two, but I like to study more than I'll ever need to pass a particular exam.

A CCNP requires knowledge of many networking concepts, and specifics as they relate to Cisco products. The Routing exam covers these concepts from an implementation and configuration perspective. In this article, I address some of the main areas to study for this new exam by mapping to the official exam objectives, which you'll find here.

Implementation and Configuration
Understanding the routing process is core knowledge for any network engineer. Routers pass both routed and routing protocol traffic to connect networks of hosts whether they're running IP, IPX or AppleTalk. The exam only focuses on IP at the Network layer. To perform their jobs correctly, routers need to know about the different network routes in the internetwork. They can learn about these through interface connections (directly connected), static routes (administratively defined) or dynamic routes (learned through routing protocol updates).

Routers maintain routing tables with the entries to networks. Each entry includes the source of the entry as defined above, a network destination, administrative distance, metric value and the interface or next hop address to reach the network.

The Administrative Distance (AD) can be defined in several ways, but it's usually defined by the type of route entry in the routing table. If the entry is via a routing protocol update, the default is based on the routing protocol. RIP has a default AD of 120; IGRP 100; Internal EIGRP 90; OSPF 110; and Internal BGP is 200. If a static route is added to the routing table, the distance is 1; the value of 0 is assigned to connected routes. Metric values, on the other hand, are calculated by routing protocol algorithms, and they can include hop count (the number of routers to pass through from point A to point B) used by RIP; a combination of bandwidth and delay used by IGRP; a composite metric used by EIGRP; a cost value used by OSPF and IS-IS; and path vectors or attributes used by BGP. The lower the administrative distance, the more preferred the route.

Routing Information Protocol (RIP) v1 and Interior Gateway Routing Protocol (IGRP) are classful routing protocols, meaning they always assume the network mask is the same throughout the internetwork. Hence, they're limited in that they can't support summarized routing information Variable Length Subnet Masks (VLSM) or Classless Inter-Domain Routing (CIDR). RIPv2, Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First (OSPF), IS-IS, and BGP are all classless routing protocols, meaning they don't assume the network mask and do support VLSM and Classless Interdomain Routing (CIDR). EIGRP is a hybrid routing protocol that can use both distance and link state, OSPF and Intermediate System-to-Intermediate System (IS-IS) also link-state routing protocols, meaning they send routing updates only when a change in the internetwork has occurred. EIGRP uses DUAL; OSPF and IS-IS use the Dijkstra algorithm for route calculations. More on this later.

Tip: To display a routers routing table, show ip route is used. Debugging can also be critical when routing tables are incomplete or incorrect. Debugging commands include debug ip rip and debug ip igrp transactions.

EIGRP
EIGRP supports many of the same technologies OSPF does, such as VLSM, no limitation of network reachability, better use of network bandwidth for routing updates, plus the support for multiple protocols IP, IPX and AppleTalk. EIGRP is much more sophisticated than Cisco's IGRP and has no real limitations except that it's Cisco proprietary and can only be used by Cisco routers. It's oftentimes referred to as a hybrid routing protocol since it uses the metrics of hop count and those seen in pure link-state routing protocols, neighbor and topology tables.

Tip: EIGRP uses the Diffusing Update Algorithm (DUAL) and supports up to four unequal paths for load balancing.

Some of the must-know EIGRP commands include show ip eigrp neighbors, ip eigrp hello-interval and ip eigrp hold-time (the latter two commands to enable the exchange of hello packets). EIGRP also uses IP multicast, address 224.0.0.10, for updates.

The six steps for a route update between routers are:

1. Hello
2. Update
3. Topology Table update
4. ACK
5. Update
6. ACK

The routers exchange what they have in their topology tables, then each router updates its own routing table. EIGRP makes use of learned routes using the DUAL algorithm and the advanced metric of Bandwidth and Delay (by default), Reliability, Load and MTU. My favorite anagram for this is Big Dogs Like Red Meat. DUAL selects routes to be added to the routing table based on feasible successors. A successor is a neighboring router used for packet forwarding that has a least-cost path to a destination. Successors are chosen much the same way; they have the next lowest-cost route. In case an EIGRP router loses its primary route, it chooses a feasible successor to the destination network. Many feasible successors can exist.

EIGRP also supports route summarization, which allows for smaller routing tables and updates while still allowing it to scale to larger networks. The command no auto-summary causes EIGRP to behave less like RIP or IGRP and more like a hybrid routing protocol with the support of link-state routing. You must also configure for summary routes by using the ip summary-address eigrp as-number address mask command on the interface that will provide the summary to the rest of the network. Load balancing across multiple links can be established with EIGRP by using the maximum-paths number command for up to six equal-cost paths and the variance command for unequal-cost paths. Verifying EIGRP operation would include the show ip eigrp neighbors, show ip eigrp topology, show ip eigrp route, show ip eigrp traffic and a series of debug commands like debug ip eigrp summary.

Tip: If two or more EIGRP routers have different k values, they won't exchange route updates.

OSPF
OSPF is a vendor-neutral routing protocol that's scalable for large internetworks, unlike RIP. OSPF also supports VLSM, has no limitation of network reachability, makes better use of network bandwidth for routing updates, provides faster routing convergence, and allows for a much smarter path selection criteria method. OSPF-configured routers use the Hello protocol to establish and maintain neighbor relationships using the IP multicast address of 224.0.0.5. The Hello protocol packet contains many things such as Router ID, intervals, neighbors, Area ID, router priority and DR and BDR IP addresses. These values are critical when it comes to discovering, choosing and maintaining OSPF routes.

Tip: The Router ID value is a 32-bit binary number that uniquely identifies the router in the OSPF autonomous system. This value is the highest IP address on any active interface and is also used to break a tie between OSPF routers when selecting the designated router (DR) and backup designated router (BDR).

To configure an OSPF router in a single Non-Broadcast Multiple Access (NBMA) area, you must be familiar with OSPF neighbor subinterface configuration. Here's where the metal meets the road. As I mentioned at the beginning of this article, my Routing exam included a few simulation questions, and one of them required the knowledge and skills to configure OSPF in an NBMA network. One interesting note: Unlike the new CCNA exam simulators, the Routing exam simulation did support the use of the (?) for simulator-supported commands. That is, you could type the question mark to get a list of supported commands that included the command you were required to use to solve the configuration issue. The exam notifies you that this is a supported feature, but reminds you that it only displays the top-level type commands. What it displays is helpful when you're working against the clock and your mind goes blank. I tried the ? command many times during my simulator but only received the necessary help for first-level commands such as show or router ospf. So while the software operates like a real router, because it's a simulator, it only supports a subset of the actual commands you can type in at the command prompt.

For OSPF configuration in a NBMA mode, the commands used are:

interface serial number.subinterface-number multipoint
router ospf process-id
network address wildcard-mask area area-id

In a NBMA mode, OSPF operates very much like it does in a broadcast network where the routers exchange update traffic to identify their neighbors and elect a DR and BDR. Configuration of neighbors is required, however, with the neighbor ip-address command, and neighbors must belong to the same subnet. Once configured, the OSPF operation can be verified with the commands show ip protocols for routing protocol configuration, show ip route ospf for routing table updates, show ip ospf neighbor and show ip ospf database.

OSPF Areas
OSPF in a multi-area internetwork creates some challenges such as frequent SPF calculations, larger routing tables and link-state tables. OSPF was designed to operate under such conditions and adds the use of hierarchical routing and intra-area routing to reduce the SPF calculations and routing table sizes. This also adds to the network new types of OSPF routers; Internal, Backbone, ABR (Area Border Router), and ASBR (Autonomous System Boundary Router). You also have to consider the six LSA types, five area types, and internal vs. external route updates types. (For brevity, I have to cut this topic short since an entire article still may not do it justice.)

Tip: There's so much to learn when it comes to OSPF, that it should probably have an exam of its own. Take the information in stride and study it many times over. Refer to multiple study resources and don't forget the hands-on.

IS-IS
IS-IS is also a vendor-neutral routing protocol, which shares similarities with OSPF and BGP. IS-IS doesn't have a backbone area like the OSPF area 0. The IS-IS backbone is a contiguous collection of Level 2-capable routers, each of which can be in a different area. An IS-IS routing domain is similar to a BGP autonomous system. A routing domain is a collection of areas under an administration that implements routing policies within the domain. A two-level hierarchy is used to support large IS-IS routing domains. A large domain may be administratively divided into areas. Each system resides in exactly one area. Routing within an area is referred to as Level 1 routing. Routing between areas is referred to as Level 2 routing. A Level 2 IS keeps track of the paths to destination areas. A Level 1 IS keeps track of the routing within its own area. For a packet destined for another area, a Level 1 IS sends the packet to the nearest Level 2 IS in its own area, regardless of what the destination area is. Then the packet travels via Level 2 routing to the destination area, where it may travel via Level 1 routing to the destination.

Tip: Be sure you understand the link cost calculation used by IS-IS, L1 and L2 router types, and the format of NSAP addresses.

To enable IS-IS and specify the area for each instance of the IS-IS routing process on a Cisco router, the followin commands are required to assign the routing process to an interface instead of a network:

router isis [area tag]
net network-entity-title
interface interface-type interface-number
ip router isis [area tag]
ipaddress ip-address-mask

Routers running IS-IS will send hello packets out all IS-IS-enabled interfaces to discover neighbors and establish adjacencies if their hello packets contain information that meet the criteria of matching authentication, IS-type and MTU size. Routers may build a link-state packet (LSP) based upon their local interfaces that are configured for IS-IS and prefixes learned from other adjacent routers, and all routers will construct their link-state database from these LSPs. Then a shortest-path tree (SPT) is calculated by each IS, and from this SPT the routing table is built.

Tip: IS-IS also supports multi-area design routing. You should be familiar with the operation and basics of configuration.

BGP
For many, border gateway protocol (BGP) has been one of the greater challenges on the Routing exam. The study resources and features surrounding BGP seem limitless. I had a vague understanding of BGP before my CCNP studies, and I'm still learning. Perhaps after years of working for a service provider or in an enterprise network, one could master the depths of this protocol.

BGP is used to connect larger networks that make up the backbone of the Internet by connecting autonomous systems. Each BGP design engineer must apply for his or her own. The Autonomous System (AS) numbers range from 1 to 65536, and the range between 64512 and 65535 are reserved for private use. BGP's uses are specific. Unless you have good understanding, multiple connections to the Internet or plenty of bandwidth, it's recommended that you use ip route prefix mask address/interface distance to create static routes when your network doesn't meet the above requirements.

BGP uses many of the familiar terminologies as mentioned for OSPF, such as internal routing and neighbors or peers. BGP between peers can be internal in an AS or between two different autonomous systems; this is referred to as external BGP (EBGP). Policy-based routing in BGP allows for definitions of data flow and the exchange of BGP routes by autonomously controlled BGP systems, such as by each service provider of the Internet. There are two types of BGP attributes used when configuring a network: well-known and optional. Of these, there are the AS-path mandatory, next-hop mandatory, local preference, and the optional MED and community. The AS-path attribute is used to identify the source of route updates and gets prepended to the route, much like a passport would show your travels. The next-hop attribute defines the neighbor responsible for the received update. The local preference attribute provides a preferred path to exit the AS. The MED or metric attribute is exchanged between autonomous systems and indicates the preferred path into the AS.

For the exam, basic BGP configuration knowledge and experience is a must. To configure routers within an AS and define the neighbor relationships, for instance, use:

router bgp 65520
neighbor 10.10.0.10 remote-as 65510
network 10.10.10.10

The aggregate-address command is used to signal the router to summarize BGP routes reducing the routing table sizes and update traffic. For verifying BGP operation, use:

show ip bgp
show ip bgp summary
show ip bgp neighbors
debug ip bgp updates

Tip: The best book on BGP is still "Internet Routing Architectures" by Sam Halabi (Cisco Press; 2000).

Extending IP Addresses
As stated earlier, EIGRP, OSPF, IS-IS and BGP are all classless routing protocols. They support CIDR and VLSM, which means hierarchical addressing and route summarization. These methods along with private addresses and NAT are the means to support IP address depletion.

Tip: VLSM works by allowing network designers and engineers to use IP addresses with variable masks because each routing update includes the mask. VLSM knowledge is required to pass this exam.

Many people refer to VLSM as the process of subnetting a subnet. Hierarchical addressing ties directly to VLSM; it works very much like a phone number, in that each number isn't maintained by each phone switch. Finally, route summarization is the last component required to minimize the depletion of IP addresses and is a means to have a single IP address represent a collection of IP addresses. The result of these methods and technologies is to minimize the size of routing tables, thereby reducing protocol traffic passed throughout the internetwork by the routers.

Tip: To pass this exam, you need to know when to use route summarization.

Everything Else
Finally, here's everything else I haven't mentioned plus topics Cisco doesn't list within the official exam objectives as posted on its Web site!

One of the more challenging topics is controlling route updates using route maps. Although they remind me of Access lists, there are differences that can cause confusion. Route maps use match commands to allow route updates between routers if the permit command is used or prevent updates if the deny statement is used. There are many different match commands such as as-path, community, interface, ip address and ip next-hop, to name a few. Then there is the series of set commands, much like that of the match commands, which allow you to configure values of the route map. An example command for BGP is neighbor ip-address/peer-group-name route-map map-name in/out to control neighbor updates. I recommend Cisco Connection Online (a private area on the Cisco Web site) for more information.

Redistribution deserves an article of its own. Cisco wants to be sure you can configure the routing protocols I've mentioned to interoperate with each other. There are many reasons to redistribute route updates from one routing protocol to another: Migration from IGRP to EIGRP, integrating a RIP and OSPF network, and enabling non-Cisco and Cisco routers to use a common routing protocol. There are the considerations to be aware of when redistributing, routing feedback or loops, incompatible routing information and inconsistent convergence times. Some of the solutions include Seed Metric and modification of the administrative distance values. You can configure redistribution between RIP for IP and OSPF since they both use the IP protocol stack. Redistribution between IGRP and EIGRP occurs automatically. Configuration is performed with the command:

redistribute protocol process-id metric metric-type route-map subnets tag

The passive-interface command can also be used here to prevent updates from exiting an interface but still allow that interface to listen for updates. Finally, the ip default-network command specifies the outside world when different major network numbers are in place.

I thought Cisco had abandoned the topic of its infamous three-layer network design model a couple of years ago when it did a major overhaul on the CCDA and introduced us to the newer more comprehensive Enterprise Composite Network Model (ECNM). Nevertheless, be sure and brush up on the three layers: Core, Distribution and Access.

IPv6 is making inroads to both the real world and the exam world. You didn't know there were two worlds? Anyhow, study the basics of IPv6 using the resource here.

Don't forget NATs. No, not those pesky creatures that are everywhere this time of year in North America, but Network Address Translation. (Ha! I'm about as funny as those Cisco engineers who wrote: "If you are reading this, you are most likely connected to the Internet and there's a very good chance that you are using Network Address Translation (NAT) right now!" It's everywhere, run for your life!) Anyway, study the resource here and you'll be ready for those pesky NAT questions.

The Routing exam is the toughest in the series for most people. It covers a ton of concepts and theory. After you pass it, the remainder of your CCNP studies will be fun and rewarding. Good luck!

Andy Barkl, CCNP, CCDP, CISSP, MCT, MCSE:Security, MCSA:Security, A+, CTT+, i-Net+, Network+, Security+, Server+, CNA, has over 19 years of experience in the IT field. He's the owner of MCT & Associates LLC, a technical training and consulting firm in Phoenix, Arizona. He spends much of his time in the classroom but has also been responsible for many Microsoft Windows 2000, Exchange 2000, and Cisco networking deployments for many clients across Arizona. He's also the online editor for MCPMag.com, TCPMag.com, CertCities.com, and a contributing author and editor for Sybex and Cisco Press. He hosts a multitude of exam preparation chats monthly on MCPmag.com, TCPmag.com and CertCities.com. You can reach him at .

More articles by Andy Barkl:

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• Securing Virtual Private Networks (642-511)