Presentation on theme: "ITEC 275 Computer Networks – Switching, Routing, and WANs"— Presentation transcript:
1 ITEC 275 Computer Networks – Switching, Routing, and WANs Week 7Robert D’AndreaSome slides provide by Priscilla Oppenheimer and used with permission
2 Agenda Learning Activities Domain Name Server (DNS) Summarization Root Owner DNSRouting tablesSpanning Tree ProtocolRapid Spanning Tree ProtocolStatic versus Dynamic RoutingRouting Protocols and Characteristics
4 Interpreting a DNS domain names DNS has a method of noting and interpreting the fully qualified path to a DNS domain name similar to the way full paths to files or directories are noted or displayed at a command prompt. For example, a directory tree path helps point to the exact location of a file stored on your computer. For Windows computers, the back slash (\) indicates each new directory that leads to the exact location of a file. For DNS, the equivalent is a period (.) indicating each new domain level used in a name.
5 Interpreting File Names UNIX uses the concept of relative and absolute file names. If a file name is preceded by a forward slash (e.g. /bin), the name is absolute. If the name is without a leading slash, it is considered relative to your current working directory. Example1: Present location is /abc/xyz, I am want to remove /abc/xyz/read/hello.txt file. Using relative path: rm read/hello.txt
6 Interpreting a DNS domain names For DNS, an example of a domain name with multiple levels is the following, a fully qualified domain name (FQDN): host-a.example.microsoft.com. Unlike the file name example, a DNS FQDN, when read from left to right (/proc/bus/usb), moves from its most specific information (the DNS name for a computer called "host-a") to its highest or most general piece of information (the trailing period (.) that indicates the root of the DNS name tree). This example shows the four separate DNS domain levels that lead away from the specific host location of "host-a":
7 Interpreting a DNS domain names 1. The "example" domain, which corresponds to a subdomain where the computer name "host-a" is registered for use. 2. The "microsoft" domain, which corresponds to the parent domain that roots the "example" subdomain. 3. The "com" domain, which corresponds to the top-level domain designated for use by business or commercial organizations that roots the "microsoft" domain. 4. The trailing period (.), which is a standard separator character used to qualify the full DNS domain name to the root level of the DNS namespace tree.
8 Root ServersWhen a computer on the Internet needs to resolve a domain name, it uses resolver software to do the lookup. A resolver breaks the name up into its labels from right to left. The first component is queried using a root server to obtain the responsible authoritative server. Queries for each name are performed until a name server returns the answer of the original query.
9 Interpreting a DNS domain names As of 2013, there are 13 root name servers, with names in the form letter.root-server.net. This does not mean that there are only 13 physical servers; each site uses redundant computer equipment to provide reliable service in when hardware and software fail on occasion.
14 Bridge Protocol Data Unit (BPDU) What are BPDUs? BPDUs are data messages that are exchanged across the switches within an extended LAN that uses a spanning tree protocol topology. BPDU packets contain information on ports, addresses, priorities and costs and ensure that the data ends up where it was intended to go. BPDU messages are exchanged across bridges to detect loops in a network topology. The loops are then removed by shutting down selected bridge interfaces and placing redundant switch ports in a backup, or blocked, state.
17 Stateless Auto-configuration Stateless Auto Configuration is an important feature offered by the IPv6 protocol. It allows the various devices attached to an IPv6 network to connect to the Internet using the Stateless Auto Configuration without requiring any intermediate IP support in the form of a Dynamic Host Configuration Protocol (DHCP) server. A DHCP server holds a pool of IP addresses that are dynamically assigned for a specified amount of time to the requesting node in a Local Area Network (LAN).
18 Stateless Auto-configuration Stateless Auto Configuration is a boon for the Network Administrators since it has automated the IP address configuration of individual network devices. Earlier, configuration of the IP addresses was a manual process requiring support of a DHCP server. However, IPv6 allows the network devices to automatically acquire IP addresses and also has provision for renumbering/reallocation of the IP addresses en masse. With a rapid increase in the number of network devices connected to the Internet, this feature was long overdue. It simplifies the process of IP address allocation by doing away with the need of DHCP servers and also allows a more streamlined assignment of network addresses thereby facilitating unique identification of network devices over the Internet.
19 Switching and Routing Choices Layer 2 transparent bridging (switching)Multilayer switchingSpanning Tree Protocol enhancementsVLAN technologiesRoutingStatic or dynamicDistance-vector and link-state protocolsInterior and exteriorEtc.
20 Selection Criteria for Switching and Routing Protocols Network traffic characteristicsBandwidth, memory, and CPU usageThe number of peers supportedThe capability to adapt to changes quicklySupport for authentication
21 Making Decisions Goals must be established Many options should be exploredThe consequences of the decision should be investigatedContingency plans should be madeA decision table can be used. Decision tables are composed of rows and columns. Each row corresponds to a single rule, with the columns defining the conditions and actions of the rules.
23 Transparent Bridging (Switching) Tasks Ethernet switches and bridges use transparent bridging.A transparent bridge connects one or more LAN segments so that end systems on different segments can communicate with each other transparently. An end system sends a frame to a destination without knowing whether the destination is local or on the other side of the bridge.
24 Transparent Bridging (Switching) Tasks Forward frames transparentlyLearn which port to use for each MAC addressFlood frames when the destination unicast address hasn’t been learned yetFilter frames from going out ports that don’t include the destination addressFlood broadcasts and multicasts
25 STP DefinitionsSTP is a bridge protocol that uses the STA (Spanning Tree Algorithm) to find redundant links dynamically and create a spanning-tree topology database. Bridges exchange BPDU (Bridge Protocol Data Unit) messages with other bridges to detect loops.BPDU STP hello packet that is sent out at configurable intervals to exchange information among bridges in the network.
26 Transparent BridgingConnectivity to different segments
27 Switching Table on a Bridge or Switch MAC AddressPortB912C-60-7C-013C-02
28 Cisco Spanning Tree Protocol Enhancements PortFast is a Cisco feature. It supports the concept of a switch edge port.UplinkFast and Backbone Fast. UpLinkFast is a Cisco feature that is configured on access layer switches. Improves the convergence time of STP.Unidirectional link detection is a hardware failure detection between switches.Loop Guard is a Cisco product. Supports the prevention of loops caused by blocking port erroneously moving to the forwarding state.
29 Redundant UplinksCoreLayerXDistribution LayerSwitch BSwitch CPrimary UplinkXSecondary UplinkAccess LayerX = blocked by STPSwitch AIf a link fails, how long will STP take to recover?Use UplinkFast to speed convergence
30 Protocols for Transporting VLAN Information Inter-Switch Link (ISL)Tagging protocolCisco proprietaryIEEE 802.1QIEEE standardVLAN Trunk Protocol (VTP)VLAN management protocol is a switch-to-switch and switch-to-router configuration.
31 Protocols for Transporting VLAN Information VLAN Trunk Protocol (VTP)The VLAN management protocol exchanges VLAN configuration changes as they are made to the network. VTP manages additions, deletions, and renaming of VLANs on a campus network without requiring manual intervention at each switch.
32 Selecting Routing Protocols They all have the same general goal:To share network reachability information among routersThey differ in many ways:Interior versus exteriorMetrics supported hop count or bandwidth.Dynamic versus static and defaultDistance-vector versus link-sateClassful versus classlessScalability
33 Interior Versus Exterior Routing Protocols Interior routing protocols are used within an autonomous systemExterior routing protocols are used between autonomous systemsAutonomous system (two definitions that are often used):“A set of routers that presents a common routing policy to the internetwork”“A network or set of networks that are under the administrative control of a single entity”
34 Routing Protocol Metrics Metric: the determining factor used by a routing algorithm to decide which route to a network is better than anotherExamples of metrics:Bandwidth - capacityDelay - timeLoad - amount of network trafficReliability - error rateHop count - number of routers that a packet must travel through before reaching the destination networkCost - arbitrary value defined by the protocol or administrator
35 Routing Algorithms Static routing Default routing Calculated beforehand, offlineDefault routing“If I don’t recognize the destination, just send the packet to Router X”Cisco’s On-Demand RoutingRouting for stub networksUses Cisco Discovery Protocol (CDP)Dynamic routing protocolDistance-vector algorithmsLink-state algorithms
36 Routing AlgorithmsStub network has only one default path to non-local hosts and no outside network knowledge. Non-local stub network traffic uses a single logical path when traveling in and out of the network.A good example would be an individual or group that uses only one router to link to an internet service provider (ISP). The individual or group are considered stub networks by the ISP.
37 Routing AlgorithmsThe default route is the IP address of the next hop when no other routes are known.To configure the default route to be :config t ip routeAn interface can be used as an alternative to and IP address. To use serial0/0 for destinations not in the routing table, use:ip route serial 0/0
38 Routing AlgorithmsA default route of a computer that is participating in computer networking is the packet forwarding rule (route) taking effect when no other route can be determined for a given Internet Protocol (IP) destination address. All packets for destinations not established in the routing table are sent via the default route. This route generally points to another router, which treats the packet the same way: If a route matches, the packet is forwarded accordingly, otherwise the packet is forwarded to the default route of that router. The process repeats until a packet is delivered to the destination. Each router traversal counts as one hop in the distance calculation for the transmission path.
39 Routing Algorithms Cisco’s On- Demand Routing The Cisco Discovery Protocol (CDP) is a Cisco proprietary protocol that, among other things, is used to discover other Cisco devices on either broadcast or non-broadcast media. CDP provides administrators with information that includes the IP address, software version, as well as the capabilities of the neighbor device.On-Demand Routing (ODR) is an enhancement to Cisco Discovery Protocol that advertises the connected IP prefix or prefixes of a stub router via CDP. ODR also supports VLSM (Variable Length Subnet Mask), which means that it can be used in just about any network.
40 Routing AlgorithmsCisco’s On- Demand RoutingODR is a feature that provides IP routing for stub sites, with minimum overhead. The overhead of a general, dynamic routing protocol is avoided without incurring the configuration and management overhead of static routing.A stub router can be thought of as a spoke router in a hub-and-spoke network topology where the only router to which the spoke is adjacent is the hub router. In such a network topology, the IP routing information required to represent this topology is fairly simple. These stub routers commonly have a WAN connection to the hub router, and a small number of LAN network segments (stub networks) are directly connected to the stub router.
41 Routing Algorithms Cisco’s On- Demand Routing It is important to know that ODR is not a routing protocol. Instead, it is simply an enhancement to CDP that is used to dynamically propagate routing information at Layer 2. The primary reasons ODR is often incorrectly referred to as a routing protocol is because it allows routers to dynamically exchange routing information. The second reason is because ODR is enabled using the router odr global configuration command.
42 Routing AlgorithmsODR allows routing information from hub/spoke topology to be exchanged with hub and entered into hub routing table without running any standard routing protocol.ODR (On Demand Routing) is designed to be used in a partially meshed environment (e.g Frame Relay networks) where a hub router maintains one link each to multiple stub routers (spokes routers). Therefore, for any spoke to communicate with another spoke, such traffic must pass through the hub.If each stub networks is simply made up of the stub router and multiple hosts (much like remote location of a corporate organization). There is no need to run any routing protocols on the stub since all host are connected and the routes can be exchanged with hub router using ODR. Hub will henceforth install the routes in routing/forwarding tables as connected routes with next-hop address of each stub respectively.
43 Routing AlgorithmsODR uses CDP protocol that runs, by default on all cisco devices. CDP is used by cisco devices to learn & retrieve basic information about their connected neighbors. Therefore, disabling CDP on a router will also disable propagation of ODR traffic.
49 Default Routing Example Routing Protocols ProvideDiscovery of new networksAutomatic route updatingBest path determinationFailover – load balancingEliminates human error
50 Default Routing Example Distance Vector Routing Protocols Neighboring routers communicate with each other to keep their routing tables updated. A view of the entire network is through all routers connected together. Link State Routing Protocols Share link information (up or down) build a routing table based on the topology that has been built.
52 Default Routing Example Router ARouter BRouter Cs0s0s0s1e0e0e0Host AHost BHost CRouterA(config)#ip routeIf it’s not local, send it to (Router B)
53 Distance-Vector Routing Router maintains a routing table that lists known networks, direction (vector) to each network, and the distance to each networkRouter periodically (every 30 seconds, for example) transmits the routing table via a broadcast packet that reaches all other routers on the local segmentsRouters update their routing table, if necessary, based on received broadcasts
55 Link-State Routing Routers send updates only when there’s a change Router that detects change creates a link-state advertisement (LSA) and sends it to neighborsNeighbors propagate the change to their neighborsRouters update their topological database if necessary
56 Distance-Vector Vs. Link-State Distance-vector algorithms keep a list of networks, with next hop and distance (metric) informationLink-state algorithms keep a database of routers and links between themLink-state algorithms think of the internetwork as a graph instead of a listWhen changes occur, link-state algorithms apply Dijkstra’s shortest-path algorithm to find the shortest path between any two nodes
58 Choosing Between Distance-Vector and Link-State Choose Distance-VectorSimple, flat topologyHub-and-spoke topologyJunior network administratorsConvergence time not a big concernChoose Link-StateHierarchical topologyMore senior network administratorsFast convergence is critical
59 Choosing between Distance Vector and Link State Protocols Routing Information Protocol (RIP) Version 1 and 2Interior Gateway Routing Protocol (IGRP)Enhanced IGRPBorder Gateway Protocol (BGP)Link-StateOpen Shortest Path First (OSPF)Intermediate System-to-Intermediate System (IS-IS)
60 Routing ProtocolsRouters talk to routers on the network, sharing information with each other.Routed protocol: IPRouting protocol: A protocol used by a router.Distance Vector routing protocols includeRIP, RIPv1, RIPv2, IGRP, and EIGRPRouters communicate with neighboring routers.Distance = Metric
61 Routing Protocols Link State routing protocols include OSPF and ISIS Routers communicate with all other routers. They exchange link state information to build a topology of the entire network.What direction of interface are you going out of?Link State refers to the interface connections or “links” to other routers and networks.
62 Routing ProtocolsConvergence is when all routers in the network have the same picture of the network.
63 Routing Information Protocol (RIP) First standard routing protocol developed for TCP/IP environmentsRIP Version 1 is documented in RFC 1058 (1988)RIP Version 2 is documented in RFC 2453 (1998)Easy to configure and troubleshootBroadcasts its routing table every 30 seconds; 25 routes per packetUses a single routing metric (hop count) to measure the distance to a destination network; max hop count is 15
64 RIP V2 Features Includes the subnet mask with route updates Supports prefix routing (classless routing, supernetting)Supports variable-length subnet masking (VLSM)Includes simple authentication to foil crackers from sending routing updates.
65 IGRP Solved Problems with RIP 15-hop limitation in RIPIGRP supports 255 hopsReliance on just one metric (hop count)IGRP uses bandwidth, delay, reliability, load(By default just uses bandwidth and delay)RIP's 30-second update timerIGRP uses 90 seconds
66 EIGRP Adjusts to changes in internetwork very quickly Incremental updates contain only changes, not full routing tableUpdates are delivered reliablyRouter keeps track of neighbors’ routing tables and uses them as feasible successorSame metric as IGRP, but more granularity (32 bits instead of 24 bits)
67 Open Shortest Path First (OSPF) Open standard, defined in RFC 2328Adjusts to changes quicklySupports very large internetworksDoes not use a lot of bandwidthAuthenticates protocol exchanges to meet security goalsIs an IP routing protocol that is completely link state.
68 OSPF MetricA single dimensionless value called cost. A network administrator assigns an OSPF cost to each router interface on the path to a network. The lower the cost, the more likely the interface is to be used to forward data traffic.On a Cisco router, the cost of an interface defaults to 100,000,000 divided by the bandwidth for the interface. For example, a Mbps Ethernet interface has a cost of 1.
69 OSPF Areas Connected via Area Border Routers (ABRs) Area 0 (Backbone)ABRABRABRArea 1Area 2Area 3
70 IS-IS Intermediate System-to-Intermediate System. Link-state routing protocol.Designed by the ISO for the OSI protocols.Integrated IS-IS handles IP also.
71 IS-IS IS-IS is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this by determining the best route for datagrams through a packet-switched network. The protocol was defined in ISO/IEC 10589:2002 as an international standard within the Open Systems Interconnections (OSI) reference design
72 Border Gateway Protocol (BGP) Allows routers in different autonomous systems to exchange routing informationExterior routing protocolUsed on the Internet among large ISPs and major companiesSupports route aggregationMain metric is the length of the list of autonomous system numbers, but BGP also supports routing based on policies
74 Internet Protocol (EGP) During the early days of the Internet, EGP version 3 (EGP3) was used to interconnect Autonomous Systems. Currently, BGP version 4 is the accepted standard for Internet routing and has essentially replaced the more limited EGP3.
75 Internet Control Message Protocol (ICMP) ICMP works at the Network layer and is used by IP for many different services. ICMP is a management protocol and messaging service for IP. Its messages are carried as IP datagrams.
76 Routing Protocols Summary Distant vector:RIP and IGRPLink-state:OSPFHybrid:EIGRP
77 SummaryThe selection of switching and routing protocols should be based on an analysis ofGoalsScalability and performance characteristics of the protocolsTransparent bridging is used on modern switchesBut other choices involve enhancements to STP and protocols for transporting VLAN informationThere are many types of routing protocols and many choices within each type
78 Review QuestionsWhat are some options for enhancing the Spanning Tree Protocol?What factors will help you decide whether distance-vector or link-state routing is best for your design customer?What factors will help you select a specific routing protocol?Why do static and default routing still play a role in many modern network designs?
79 This Week’s Outcomes Spanning Tree Protocol Rapid Spanning Tree ProtocolStatic versus Dynamic RoutingRouting Protocols and Characteristics