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STUDY GUIDES SAMPLE TESTS FORUMS AUDIO TRAINING VIDEO TRAINING EXAMSHEETS HELP US OUT LINKS DIRECTORY NEWSLETTERS COLLEGE DEGREES FAQ ARTICLES BOOK REVIEWS ADVERTISE TIPS/TRICKS TOPSITES CONTACT		640-503 BSCN (Building Scalable CISCO Networks) This study guide is developed to provide you with an overview of the Cisco 503 BSCN subject. You are suggested to use this study guide to give yourself a “bird eye view” of the exam. For further study and more in-depth coverage of the topics, the following books are strongly recommended: Building Scalable Cisco Networks: Prepare for CCNP and CCDP Certification with the Official Cisco BSCN Coursebook by Catherine Paquet, Diane Teare, Thomas M. Kelly CCNP Building Scalable Cisco Networks Study Guide (Exam 640-503) by Syngress Media Inc(Editor) (Hardcover) =========================================================== Do NOT use this study guide as your sole study resource. Successful completion of the 503 exam requires both practical experience as well as lots and lots of reading. On the actual exam you will encounter questions on IOS commands. Cisco’s original documentation has very detailed coverage on these commands. You may follow the links we provide to read these original Cisco documents for more information on the commands. =========================================================== Readings from the Cisco Web Site Configuring IP Routing Protocols: http://www.cisco.com/univercd/cc/td/doc/product/software/ios11/acbook/aciprout.htm IP Routing Protocol Commands: http://www.cisco.com/univercd/cc/td/doc/product/software/ssr921/cscr/79711.htm Designing & Implementing an OSPF Network: http://www.cisco.com/cpress/cc/td/cpress/design/ospf/on0407.htm OSPF Design Guide: http://www.cisco.com/warp/public/104/2.html OSPF FAQ: http://www.cisco.com/warp/public/104/9.html BGP Information: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/bgp.htm BGP Case Study: http://www.cisco.com/warp/public/459/bgp-toc.html BGP Commands: http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_r/iprprt2/1rdbgp.htm EIGRP: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/en_igrp.htm EIGRP FAQ: http://www.cisco.com/warp/public/103/eigrpfaq.html Configuring EIGRP: http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/np1_c/1cprt1/1ceigrp.htm Skills Measured Simplifying IP address management and centralizing addresses Deploying link-state protocols and redistribution Deploying single or multihomed interconnection into a BGP network Interconnect the BGP clouds Using multiple routed and routing protocols Routing and Switching Switching forwards packets from an inbound interface to an outbound interface Routing forwards traffic to the destination network by passing packets to the next-hop router on the delivery path Routing table contains all the important routing information Within the routing table, entries can be listed in an efficient search order to simplify the search mechanism. Also, multiple paths to a destination are allowed. To refresh the routing entries, you may use the clear ip route command Lower administrative distance is always preferred Manually entered routes are preferred to dynamically learned routes in small environment Sophisticated metrics are preferred over simple metric structures in large environment RIP’s routing metric is determined by hop count, and by default supports IP load balancing IGRP’s composite routing metric is based on bandwidth, delay, reliability, load, and MTU. By default it supports IP load balancing Neighboring routers and routing protocols exchange frames by means of Hello packets or Routing update packets Route filtering is similar to packet filtering, as it is also based on access-lists You may restrict certain routing information to and from particular neighbors by deploying: Distribute lists Prefix lists Provider Connections · 3 major types of provider connections: o Default routes from all providers Provider sends BGP default route, while AS sends all routes to provider Low memory consumption Low CPU usage o Customer routes and default routes from all providers The shortest AS-path is the best path You can override the path choice Medium memory consumption Medium CPU usage o Full routes from all providers Consumes lots of memory and CPU time The shortest AS-path is the best path You can override the path choice Classful Operation Based on the distance vector method of route calculation Examples include RIPv1 and IGRP With the distance vector method, routing updates are propagated to only the directly connected neighbors Routing masks are not carried with the periodic routing updates, and that sub-net routes are shared by devices within the same network All router interfaces on the same network must use the same subnet mask - waste of host addresses Classless Operation Routing masks are carried with the route advertisement Examples include OSPF, EIGRP, RIPv2, IS-IS and BGP With the link state method, announcements are propagated to all devices in the routing domain Router interfaces on the same network can have different subnet masks Variable-length subnet masking VLSM is supported to maximize the allocation of available host addresses Addressing The current problem with addressing is that IP addresses are going to exhaust soon. Also, the fast growth in the size of routing table makes routing inefficient IP addresses are represented in 32-bit dotted decimal, with a total of 5 classes available: --Class A 001 - 126 --Class B 128 - 191 --Class C 192 - 223 --Class D 224 - 239 --Class E 240 - 254 OSPF uses 224.0.0.5 and 224.0.0.6 RIPv2 uses 224.0.0.9 EIGRP uses 224.0.0.10 VLSM does not have the limitation of the classful structure Routing protocols can summarize addresses of several networks into one address to reduce the burden of route processing, given the conditions that: Multiple IP addresses have the same highest-order bits Routing protocols carry the subnet mask length Since RIPv1 and IGRP do not advertise subnets, they cannot support discontiguous subnets OSPF, EIGRP, and RIPv2 can advertise subnets and support discontiguous subnets With CIDR Classless Interdomain Routing, blocks of Class C addresses are assigned to the ISPs, and the ISPs assign subsets of address space to different organizations. Also, blocks are summarized in the routing tables. With hierarchical addressing, you can have a contiguous address assignment to allow the efficient use of addresses. Also, you can reduce the number of routing table entries for participating routers. OSPF Link-state protocol Types of Link-State Advertisements include: Type 1: Router link entry Type 2: Network link entry Type 3: Summary link entry Type 4: Same as Type 3 Type 5: AS external link entry Uses protocol number 89 Fast convergence VLSM compatible Supports path selection based on bandwidth Supports equal cost multi-path During the election of DR and BDR, hello packets are exchanged via IP multicast (with the address of 224.0.0.5), and then the router with the highest OSPF priority is elected In large areas, problems can include: Too much LSA SPF runs too often Routing table too big Solutions for large area: Use OSPF Hierarchical Routing Deploy the concept of areas and autonomous systems to minimize routing update traffic In general there is a single exit point into an area If multiple exit points exist, nonoptimal paths may be selected Why would you prefer OSPF rather than RIP Version1? In general Link-State protocols have faster convergence. OSPF will select paths based on available bandwidth, effectively avoid the hop count limitation. OSPF supports VLSM, while RIP V1 does not. RIP v1 updates are not compatible with VLSM because it does not have a subnet field in its update packet An OSPF ASBR can redistribute routing information with routers in other areas NBMA Nonbroadcast Multiaccess Single interface interconnects multiple sites Multiple routers without broadcasting OSPF has certain restrictions in an NBMA environment: Neighbors must be manually configured Hellos not sent to 224.0.0.5 Note that OSPF treats NBMA as other broadcast media DR and BDR need to have complete connectivity with all other routers, plus a list of neighbors Subinterfaces (physical interface split into multiple logical interfaces) are typically used in NBMA topologies that are point-to-point or multipoint On low-speed NBMA media, the default EIGRP hello interval is 60 seconds Virtual Links for Backbone Area Provide path to backbone Can be used to link discontiguous backbone for Merged networks, Redundancy or Point-to-point links To view the status of all OSPF virtual links, use the sh ip ospf virtual-1 command EIGRP Advanced distance vector protocol which is 100% loop free and supports incremental updates Supports VLSM, discontiguous networks and classless routing Uses 32bit metric (IGRP uses 24 bit) Composite metric for picking the best path: Metric = bandwidth + delay by default Compatible with IGRP networks Supports multi protocols Uses multicast Does not use broadcast Supports unequal cost path load balancing Supports different types of WAN links, including Point-to-point, NBMA Multipoint and Point-to-point Route summarization has a default mode of classful network boundaries. However, you may manually configure the arbitrary network boundaries mode Types of packets: Hello – for establishing neighbor relationships Update – for sending routing updates Query – for asking the neighbors for routing information Reply – for responding to query on routing information ACK – for acknowledging reliable packet Reliable packets - packets that require explicit acknowledgement, such as Update, Query and Reply. Router has a neighbor list and a retransmission list. Reliable packets will be retransmitted when there is no acknowledgment received Neighbor relationship is reset when the max retry limit of 16 is reached Unreliable packets - packets that do not require explicit acknowledgement, such as Hello and ACK Automatic Summarization Subnetworks are summarized to a single classful network It is on by default Manual Summarization Based on a per-interface basis Immediately creates a route pointing to null zero Includes Loop prevention mechanism Load Balancing Routes with metric = minimum metric (equal cost) will be installed in the routing table Max 6 entries in the routing table for the same destination, although the default is 4 Unequal-cost load balancing can be achieved with the variance command You are encouraged to limit the size, the scope of Updates, and the queries by using summary address and filters For EIGRP to be scalable, good design methods are needed to ensure that each region can have a contiguous address space to make route summarization possible. Also, a tiered network design model is recommended EIGRP: is not considerably a very complex protocol, does not provide client address conflict resolution, and does not support compression over the WAN link DUAL Diffusing Update Algorithm Tracks all the routes advertised by neighbors and select the loop-free path using a successor, plus remembering any feasible successors If the successor is lost, uses a feasible successor. If there is no feasible successor, queries the neighbors and re-computes for any new successor BGP Border Gateway Protocol Enhanced distance vector protocol Runs on top of TCP port 179 Uses Incremental triggered updates Uses path vectors or attributes as metrics Uses TCP for reliable session management Uses the concept of autonomous system (AS) - collection of networks under single administration IGP works within an autonomous system EGP works within different autonomous systems BGP work between autonomous systems for exchange of loop-free routing information Avoid using BGP when there is only a single connection to the Internet or other AS; there is a lack of memory or processor power; there is not enough bandwidth between autonomous systems You may use the ip route prefix mask {address \| interface } [distance] command to create static route in place of BGP The concept of Communities - tag routes to ensure consistent filtering as well as route-selection policy. Note that any BGP router can tag as well as filter routes in incoming and outgoing routing updates. However, communities are stripped in outgoing BGP updates with the default setting. With Cisco router we have the weight attribute which call for paths with the highest weight value to be the most desirable route. This attribute is configured on the routers on a per-neighbor basis, and is not sent from / to any BGP neighbors. Peer Group allows you to define a template with parameters set for a group of neighbors. This can be pretty useful if there are many neighbors that share the same outbound policies --- outbound only, as the members can still have different inbound policies. A BGP peer is a BGP neighbor that the router has formed a TCP connection with A BGP peer can also be another BGP router You may use the aggregate-address ip-address mask [summary-only] [as-set] command to create an aggregate entry. The summary-only option allows you to advertise only the summary routes. The as-set option allows you to include the list of AS numbers that the more specific routes have passed through. In the case of providers, redistribution into IGP is required if not all routers are running BGP, and that external route knowledge is required. IBGP is being used within an AS EBGP is being used between different ASs Route Reflector BGP split horizon implies that those routes that are learned via IBGP are not propagated to other IBGP peers, meaning you will need to have a full-mesh IBGP Full mesh IBGP can have way too many sessions with the increase in the number of routers – this is not desirable Configuring BGP for full mesh will kill your router’s RAM and CPU, if your routing environment is large Fully meshed with IBGP Modifies the BGP split horizon rule to solve the IBGP full-mesh problem No negative impact on packet forwarding You can deploy multiple route reflectors You can deploy multiple levels of route reflectors Can work with regular BGP peers Route reflector works by dividing AS into multiple clusters There must be a minimum of one route reflector per cluster Uses only a single IGP to carry next-hop as well as local routes One of the most common BGP commands for configuring a Route Reflector is bgp cluster-id [cluster-id] Note that setting the route reflectors peer ID has nothing to deal with BGP MED 3 valid ways for routing information from an AS into the BGP table include: Redistribution from existing IGP Redistribution from static route Commands Redistribution Can take place only in multi protocol environment Routes can be learned from another routing protocol during the redistribution process The seed metric for a route is derived from being directly connected to an interface on the router Redistributed routes are NOT connected in a physical way You can run the default-metric command to establish the seed metric for the route The established metric will increment automatically You should set the default metric to be larger than the largest native metric available Typical protocol selection factors: Determine the administrative distance Decide on which metric is the best for you Protocols supported include: Border Gateway Protocol (BGP) Connected Exterior Gateway Protocol (EGP) Enhanced Interior Gateway Routing Protocol (EIGRP) Interior Gateway Routing Protocol (IGRP) ISO IS-IS IGRP for OSI networks Mobile routes On Demand stub Routes Open Shortest Path First (OSPF) Routing Information Protocol (RIP) Static routes The Seed Metric being used when performing route redistribution in EIGRP include: Bandwidth Load MTU Delay Reliability Route Map Numbered For use with Policy Based Routing Similar to complex access lists Statements included the route maps are numbered You may always insert and delete statements in a route map You may edit the match conditions in a statement Matched route can be modified with the set command Commands needed to create a Route Map include: Match Set route-map When a Match is made, the route will be changed with the set command The Match command is in a format similar to the access-list statements Policy Based Routing Available since IOS Release 11 Implemented with route maps To selectively cause packets to take different paths To mark traffic with different TOS TOS is usually used with queuing Supports load sharing Multiple paths are used based on the many different traffic characteristics Policies are applied to incoming packets This study guide is developed in Year 2001 by Yu Chak Tin Michael. His personal web site is located at: http://michaelyu.freeservers.com. You may also email him at: ycthk@i-cable.com Copyright 2000 http://www.CERTguide.com/