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Week Ten AgendaAttendanceAnnouncementsData Center Design updateFinal exam 150 pointsNo class July 4 (Monday)Make-up class on Friday July 8.Review Week Nine InformationCurrent Week InformationUpcoming AssignmentsWeek Ten TopicsRouting ProtocolsRouting TableStatic versus dynamic routingInterior Versus Exterior Routing ProtocolsWhat is convergence?Autonomous SystemsDefinitionsLoop Free Path

Routing ProtocolsOne of the primary jobs of a router is to determine the best path to a given destination

A router learns paths, or routes, from the static configuration entered by an administrator or dynamically from other routers, through routing protocols

Routing Table PrinciplesThree principles regarding routing tables: Every router makes its decisions alone, based on the information it has in its routing table.Different routing table may contain different informationA routing table can tell how to get to a destination but not how to get back (Asymmetric Routing)Routing Table ObjectiveTo forward a packet towards its destination network, which is the destination IP address of the packet. To do this, a router needs to search the routing table for this stored information.

Routing TablesRouters keep a routing table in RAMA routing table is a list of the best known available routesRouters use this table to make decisions about how to forward a packetOn a Cisco router, the show IP route command is used to view the TCP/IP routing tableA routing table maps network prefixes to an outbound interface.

Routing Table Specifics

Routing TableWhen RTA receives a packet destined for 192.168.4.46, it looks for the prefix 192.168.4.0/24 in the routing tableRTA then forwards the packet out an interface, such as Ethernet0, as directed in the routing table

Routing LoopsA routing loop is a network problem in which packets continue to be routed in an endless circleIt is caused by a router or line failure, and the notification of the downed link has not yet reached all the other routersIt can also occur over time due to normal growth or when networks are merged togetherRouting protocols utilize various techniques to lessen the chance of a routing loop

Routing Table SpecificsDirectly connected networks-this occurs when a device is connected to another router interfaceRemotely connected networks-this is a network that is not directly connected to a particular router network/next hop associations-about the networks include source of information, network address & subnet mask, and Ip address of next-hop router

The show ip route command is used to view a routing table on a Cisco router

Routing Table Specifics

Routing ProtocolsDirectly Connected Routes-To visit a neighbor, you only have to go down the street on which you already live. This path is similar to a directly-connected route because the "destination" is available directly through your "connected interface," the street.

Static RoutingStatic Connected Routes-A train uses the same railroad tracks every time for a specified route. This path is similar to a static route because the path to the destination is always the same.

Application For Static Routing When network only consists of a few routersUsing a dynamic routing protocol in such a case does not present any substantial benefit. Network is connected to Internet only through one ISPThere is no need to use a dynamic routing protocol across this link because the ISP represents the only exit point to the Internet

Application For Static Routing Static routing is not suitable for large, complex networks that include redundant links, multiple protocols, and meshed topologiesRouters in complex networks must adapt to topology changes quickly and select the best route from multiple candidatesWhen an interface goes down, all static routes mapped to that interface are removed from the IP routing table

Application For Static RoutingHub and spoke topology is used on a large networkA hub-and-spoke topology consists of a central location (the hub or switch) and multiple branch locations (spokes), with each spoke having only one connection to the hub or switch. Using dynamic routing would be unnecessary because each branch has only one path to a given destination-through the central location.Static routing is useful in networks that have a single path to any destination network. Static Routes in Routing TableIncludes: network address and subnet mask and IP address of next hop router or exit interfaceDenoted with the code S in the routing tableRouting tables must contain directly connected networks in order to connect remote networks, before static or dynamic routing can be usedStatic Routing

Static RoutingThe corporate network router has only one path to the network 172.24.4.0 connected to RTYA static route is entered on RTZ

Static Routing

Routing ProtocolsDynamic Routes-When driving a car, you can "dynamically" choose a different path based on traffic, weather, or other conditions. This path is similar to a dynamic route because you can choose a new path at many different points on your way to the destination.

Dynamic Routing ProtocolAre used to add remote networks to a routing tableAre used to discover networksAre used to update and maintain routing tables

Dynamic Routing ProtocolAutomatic network discoveryNetwork discovery is the ability of a routing protocol to share information about the networks that it knows about with other routers that are also using the same routing protocol. Dynamic routing protocols are used to share routing information with other routers and to maintain an up-to-date routing table.Dynamic routing protocols not only make a best path determination to various networks, they will also determine a new best path if the initial path becomes unusable (or if the topology changes)

Dynamic Routing Protocol

Configuring Dynamic Routing ProtocolsDynamic routing of TCP/IP can be implemented using one or more protocols which are often grouped according to where they are used.

Routing protocols designed to work inside an autonomous system are categorized as interior gateway protocols (IGPs).

Protocols that work between autonomous systems are classified as exterior gateway protocols (EGPs).

Protocols can be further categorized as either distance vector or link-state routing protocols, depending on their method of operation.

Path CostsPath costs are an arbitrary value, based on hop count, bandwidth, or other calculation, that is typically assigned by a network administrator and used by the routing protocol to compare different routes through an internetwork. Routing protocols use cost values to select the best path to a certain destination: lowest cost identifies the best path.

Interior Versus Exterior Routing ProtocolsAn interior gateway protocol (IGP) is a routing protocol that is used within an autonomous system (AS). Two types of IGP.Distance-vector routing protocols each router does not possess information about the full network topology. It advertises its distances to other routers and receives similar advertisements from other routers. Using these routing advertisements each router populates its routing table. In the next advertisement cycle, a router advertises updated information from its routing table. This process continues until the routing tables of each router converge to stable values.Interior Versus Exterior Routing ProtocolsDistance-vector routing protocols make routing decisions based on hop-by-hop. A distance vector routers understanding of the network is based on its neighbors definition of the topology, which could be referred to as routing by RUMOR.

Route flapping is caused by pathological conditions (hardware errors, software errors, configuration errors, intermittent errors in communications links, unreliable connections, etc.) within the network which cause certain reach ability information to be repeatedly advertised and withdrawn.Interior Versus Exterior Routing ProtocolsIn networks, with distance vector routing protocols flapping routes can trigger routing updates with every state change. Cisco trigger updates are sent when these state changes occur. Traditionally, distance vector protocols do not send triggered updates.Interior Versus Exterior Routing ProtocolsLink-state routing protocols, each node possesses information about the complete network topology. Each node then independently calculates the best next hop from it for every possible destination in the network using local information of the topology. The collection of best next hops forms the routing table for the node.This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbors. In a link-state protocol, the only information passed between the nodes is information used to construct the connectivity maps.Routing ProtocolsInterior routing protocols are designed for use in a network that is controlled by a single organization

RIPv1 RIPv2, EIGRP, OSPF and IS-IS are all Interior Gateway Protocols

Link State AnalogyEach router has a map of the networkEach router looks at itself as the center of the topologyCompare this to a you are here map at the mallThe map is the same, but the perspective depends on where you are at the time You Link State Routing ProtocolThe link-state algorithm is also known as Dijkstra's algorithm or as the shortest path first (SPF) algorithm

The link-state routing algorithm maintains a complex database of topology information

The link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. They have a complete picture of the network

Link State Analogy

Distant Vector Versus Link State Distant Vectors Routing Protocols Link State Routing ProtocolsRIP (v1 and v2)OSPFEIGRP (hybrid)IS - ISExterior Gateway Routing ProtocolAn exterior routing protocol is designed for use between different networks that are under the control of different organizationsAn exterior routing routes traffic between autonomous systemsThese are typically used between ISPs or between a company and an ISPBGPv4is the Exterior Gateway Protocol used by all ISPs on the Internet

EGI and EGP Routing Protocol

What is ConvergenceRouters share information with each other, but must individually recalculate their own routing tables For individual routing tables to be accurate, all routers must have a common view of the network topology When all routers in a network agree on the topology they are considered to have converged

Why is Quick Convergence Important?When routers are in the process of convergence, the network is susceptible to routing problems because some routers learn that a link is down while others incorrectly believe that the link is still up

It is virtually impossible for all routers in a network to simultaneously detect a topology change.

Convergence IssuesFactors affecting the convergence time include the following:Routing protocol used Distance of the router, or the number of hops from the point of change Number of routers in the network that use dynamic routing protocols Bandwidth and traffic load on communications links Load on the router Traffic patterns in relation to the topology change What are Autonomous Systems?An Autonomous System (AS) is a group of routers that share similar routing policies and operate within a single administrative domain.

An AS can be a collection of routers running a single IGP, or it can be a collection of routers running different protocols all belonging to one organization.

In either case, the outside world views the entire Autonomous System as a single entity.

Autonomous System AS NumbersEach AS has an identifying number that is assigned by an Internet registry or a service provider. This number is between 1 and 65,535. AS numbers within the range of 64,512 through 65,535are reserved for private use. This is similar to RFC 1918 IP addresses.

Because of the finite number of available AS numbers, an organization must present justification of its need before it will be assigned an AS number.

An organization will usually be a part of the AS of their ISP

Autonomous System

Autonomous SystemEach AS has its own set of rules and policies.The AS number uniquely distinguish it from other ASs around the world.DefinitionsMetric is a numeric value used by routing protocols to help determine the best path to a destination.RIP uses the metric hop count number . The lower the numeric value, the closer the destination.OSPF uses the metric bandwidth.EIGRP uses bandwidthDefinitionsFlat routing protocol is when all routing information is spread through the entire network.Hierarchical routing protocol are typically classless link-state protocols. Classless link-state protocols route updates and subnet masks in their routing updates. Draw diagram Administrative distance is the measure used by Cisco routers to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol. Each routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. A lower numerical value is preferred.Administrative Distance

EIGRP Characteristics

EIGRP is an advanced distance vector protocol that employs the best features of link-state routing.

OSPF CharacteristicsOSPF is the standardized protocol for routing IPv4. Since its initial development, OSPF has been revised to be implemented with the latest router protocols.Developed for large networks (50 routers or more)Must be a backbone areaRouters that operate on boundaries between the backbone and non-backbone are called, Area Border Routers (ABR)OSPF is a link state protocolOSPF CharacteristicsWhen the OSPF topology table is fully populated, the SPF algorithm calculates the shortest path to the destination. Triggered updates and metric calculation based on the cost of a specific link ensure quick selection of the shortest path to the destination.

OSPF Characteristics

OSPF is link-state routing protocolRIP and EIGRP are distance-vector (routing by rumor) routing protocols, susceptible to routing loops, split-horizon, and other issues.OSPF has fast convergenceRIP hold-down timers can cause slow convergence.OSPF supports VLSM and CIDRRIPv1 does notOSPF CharacteristicsCiscos OSPF metric is based on bandwidthRIP is based on hop countOSPF only sends out changes when they occur.RIP sends entire routing table every 30 seconds, IGRP every 90 seconds OSPF also uses the concept of areas to implement hierarchical routingA large internetwork can be broken up into multiple areas for management and route summarizationOSPFCharacteristicsTwo open-standard routing protocols to choose from:

RIP, simple but very limited, or OSPF, robust but more sophisticated to implement.EIGRP is Cisco proprietary

OSPFCharacteristicsAutonomous System Boundary Router (ASBR) is an area border router placed between an OSPF autonomous system and a non-OSPF network that operates both OSPF and an additional routing protocol, such as RIP. ASBRs must be located in a non-stub OSPF area.OSPF Characteristics

OSPF CharacteristicsWhen all routers are configured into a single area, the convention is to use area 0(zero)If OSPF has more than one area, it must have an area 0Multi-area OSPF becomes more complicated to configure and understandOSPF Routing DomainSingle Area OSPF uses only one area, usually Area 0

OSPF Characteristics1. Flooding of link-state informationThe first thing that happens is that each router, on the network announces its own piece of link-state information to all other routers on the network. This includes who their neighboring routers are and the cost of the link between them.Example: Hi, Im Router A, and I can reach Router B via a T1 link and I can reach Router C via an Ethernet link.Each router sends these announcements to all of the routers in the network.OSPF Characteristics

OSPF Characteristics2. Building a Topological DatabaseEach router collects all of this link-state information from other routers and puts it into a topological database.3. Shortest-Path First (SPF), Dijkstras AlgorithmUsing this information, the routers can recreate a topology graph of the network.Believe it or not, this is actually a very simple algorithm and I highly suggest you look at it some time, or even better, take a class on algorithms.

OSPF Characteristics4. Shortest Path First TreeThis algorithm creates an SPF tree, with the router making itself the root of the tree and the other routers and links to those routers, the various branches.5. Routing TableUsing this information, the router creates a routing table.

Large OSPF NetworksLarge link-state tableEach router maintains a LSDB for all links in the areaThe LSDB requires the use of memoryFrequent SPF calculationsA topology change in an area causes each router to re-run SPF to rebuild the SPF tree and the routing table.A flapping link will affect an entire area.SPF re-calculations are done only for changes within that area.

Issues with large OSPFNetworksLarge routing tableTypically, the larger the area the larger the routing table.A larger routing table requires more memory and takes more time to perform the route look-ups.Solution: Divide the network into multiple areasLink-State Advertisement (LSA) is contained inside the link-state packets (LSPs), these advertisements are usually multicast packets, containing information about neighbors and path costs, that are employed be link-state protocols. Receiving routers use LSAs to maintain their link-state databases and, ultimately, routing tables.OSPF Uses Areas

Hierarchical routing enables you to separate large internetworks (autonomous systems) into smaller internetworks that are called areas.

With this technique, routing still occurs between the areas (called inter-area routing), but many of the smaller internal routing operations, such as recalculating the database re-running the SPF algorithm, are restricted within an area OSPF Uses Areas

Changes in one area are generally not propagated (spread) to another

Route summarization is extensively used in multi-area OSPFOSPF Router Types

OSPF Router TypesInternal: Routers with all their interfaces within the same area Backbone: Routers with at least one interface connected to area 0 ASBR:(Autonomous System Boundary Router): Routers that have at least one interface connected to an external internetwork (another autonomous system)ABR: (Area Border Router): Routers with interfaces attached to multiple areas. IS - IS CharacteristicsIS-IS is an Open System Interconnection (OSI) routing protocol originally specified by International Organization for Standardization (ISO)IS-IS is a dynamic, link-state, intra-domain, interior gateway protocol (IGP)IS-IS was designed to operate in an OSI Connectionless Network Service (CLNS) environmentIt was not originally designed to work with the IP protocol

IS - IS CharacteristicsExtensions were added so that IS-IS can route IP packetsIS-IS operates at Layer 3 (Network) of the OSI modelIS-IS selects routes based upon a cost metric assigned to links in the IS-IS networkA two-level hierarchy is used to support large routing domainsA large domain can be administratively divided into areas

OSPF and IS IS SimilaritiesClasslessLink-state databases an Dijkstras algorithmHello packets to form and maintain adjacenciesUse areas to form hierarchical topologiesSupport address summarization between areasLink-state representation, aging, and metricsUpdate, decision, and flooding processesConvergence capabilitiesDeployed on ISP backbonesIS IS and the OSI Protocol SuiteThe OSI suite of protocols were never widely implemented at the Layers 3-7 because the TCP/IP Protocols at these layers became the de-facto standard.

Layers 1 and 2 Protocols are widely used: IEEE 802.3, FDDI, IEEE 802.5, etc.

Link State Routing AnalogyThe Link State Database is similar to a map in a shopping mall. All maps in the mall is the same, just as the LSDB is the same in all routers within an area. The only real physical difference in the maps is you are at what dot. By looking at your position in relation to where you want to go, you can determine the best way to get to your destination. Link state routers calculate the best path to every network within the area, from their own perspective.

OSI TerminologyEnd system (ES) is any non-routing network node (host)Intermediate system (IS) is a routerAn area is a logical entity formed by a set of contiguous routers, hosts, and the data links that connect themDomain is a collection of connected areas under a common administrative authority(think AS)The areas are connected to form a backbone

IS IS is Designed to be HierarchicalAn OSI network is a hierarchy of these entities:Domain -any portion of an OSI network under a common administrationArea a part of a domain, broken up for easier managementBackbone areas connect to other areas through the backbone

IS IS is HierarchicalThere are four levels of routing:Level 0, routing between an ES (end system) and IS (intermediate system).Level 1, routing between ISs in the same areaLevel 2, routing between different areas in the same domainLevel 3, routing between separate domains

IS IS is Hierarchical

Why use IS IS instead of OSPF?IS-IS is more scalable than OSPF because it uses smaller LSPs (Link-State Protocol) for advertisementsUp to 1000 routers can reside in an IS-IS area versus several hundred for OSPFIS-IS is more efficient with its updates and requires less CPU powerIS-IS has more timers that can be fine-tuned to speed up convergence

EIGRP CharacteristicsCisco proprietary, released in 1994EIGRP is an advanced distance-vector routing protocol that relies on features commonly associated with link-state protocols. (sometimes called a hybrid routing protocol)Supports VLSM and CIDRUses multicasts for communication not broadcastsEstablishes adjacencies with its neighbor routers by using a Hello protocolKeeps all routes in a topology tableHas speed and efficiency of routing updates like a link-state protocol

EIGRP Metric CalculationBy default, EIGRP uses only these:Bandwidth (carrying capacity)Delay (end-to-end travel time)If these are the default:Bandwidth (default)Delay (default)When are these used?loadReliabilityThese values are used when the administrator manually enters them

EIGRP TerminologyEIGRP uses DUAL, the Diffusing Update Algorithm to calculate routes not Bellman-Ford algorithm.The lowest cost path to a destination is called the feasible distance (FD) The cost of the route as advertised by the neighboring router, is called reported distance (RD) The best (primary) route to a destination is called the successor route (successor)The next best route, (backup), if there is one, is called the feasible successor (FS)

EIGRP TablesThe following three tables are maintained by EIGRP:Neighbor table Topology table Routing table

BGP

BGP is a path vector routing protocol.Defined in RFC 1772BGP is a distance vector routing protocol, in that it relies on downstream neighbors to pass along routes from their routing table.BGP uses a list of AS numbers through which a packet must pass to reach a destination.BGP Basics

Exchange routing information between autonomous systems Guarantee the selection of a loop free path. BGP4 is the first version of BGP that supports CIDR and route aggregation. Common IGPs such as RIP, OSPF, and EIGRP use technical metrics. BGP does not use technical metrics. BGP makes routing decisions based on network policies, or rules (later)BGP does not show the details of topologies within each AS.BGP sees only a tree of autonomous systems.BGP BasicsBGP updates are carried using TCP on port 179. In contrast, RIP updates use UDP port 520OSPF, IGRP, EIGRP does not use a Layer 4 protocol Because BGP requires TCP, IP connectivity must exist between BGP peers. TCP connections must also be negotiated between them before updates can be exchanged. Therefore, BGP inherits those reliable, connection-oriented properties from TCP.

Loop Free Path

To guarantee loop free path selection, BGP constructs a graph of autonomous systems based on the information exchanged between BGP neighbors. BGP views the whole internetwork as a graph, or tree, of autonomous systems. The connection between any two systems forms a path. The collection of path information is expressed as a sequence of AS numbers called the AS Path. This sequence forms a route to reach a specific destinationBGP Operation

When two routers establish a TCP-enabled BGP connection between each other, they are called neighbors or peers.

Each router running BGP is called a BGP speaker.Upcoming DeadlinesMimic Simulator Lab Assignment 4-1-2, Basic Routing and LAN Switching Configuration due June 27, 2011Assignment1-4-3 Data Center Design ProjectPhase 3: Data Center Network Design due July 11, 2011.Assignement10-1 Concept Questions 7 is due July 4, 2011.