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Routing Eng. Rania Adel Computer Network Dep. Outline Operating Cisco IOS – ICND1 -> CH: 13 Routing Protocol Concepts -> ICND1 -> CH:14 Routing – ICND2 CH: 8 Integrated Service Router (ISR) The ISR combines features such as routing and LAN switching functions, security, voice, and WAN connectivity into a single device. The Cisco 1841 is a relatively low cost ISR designed for small to medium-sized businesses and small enterprise branch offices. Integrated Service Router (ISR) System Power LED (SYS-PWR) System Activity (SYS ACT) Indicates power is received and that the internal power supply is functional. LED is solid green. A blinking LED indicates the system is actively transferring packets. Integrated Service Router (ISR) Modular Slot 1 with a High-speed WAN Interface Card (HWIC): Modular slots can be used for different types of interfaces. The HWIC shown here provides serial connectivity over a wide-area network. Integrated Service Router (ISR) Compact Flash Module: This removable module is used to store the Cisco IOS and other operating software for the ISR. Integrated Service Router (ISR) Single Slot USB Port: The USB Flash feature allows users to store images and configurations and boot directly via USB Flash memory. Integrated Service Router (ISR) Fast Ethernet Ports: These ports provide 10/100 Mbps connectivity for local area networks. Integrated Service Router (ISR) Console Port: This port is used to configure the ISR via a directly connected host. Integrated Service Router (ISR) Auxiliary Port: This port is used to configure the ISR via a modem connection. Integrated Service Router (ISR) Modular Slot 0 with a Four Port Ethernet Switch: Modular slots can be used for different types of interfaces. The four port Ethernet card shown here provides LAN connectivity to multiple devices. Cisco Router Components Bootstrap ◦ Stored in ROM ◦ Brings up the router during initialization ◦ It will boot the router and then load the IOS. POST (power-on self-test) ◦ Stored in ROM ◦ Checks the basic functionality of the router hardware and determines which interfaces are present. Cisco Router Components ROM monitor ◦ Stored in ROM ◦ Used for testing and troubleshooting Mini-IOS ◦ Called the RXBOOT or boothelper ◦ The mini-IOS is a small IOS in ROM ◦ It can be used to bring up an interface and load a Cisco IOS into flash memory Cisco Router Components ROM (read-only memory) ◦ Used to start and maintain the router ◦ Holds the POST and the bootstrap program, as well as the mini-IOS RAM (random access memory) ◦ Used to hold packet buffers, ARP cache, routing tables, and also the software and data structures that allow the router to function. ◦ Running-config is stored in RAM, and most routers expand the IOS from flash into RAM upon boot. Cisco Router Components Flash memory ◦ Stores the Cisco IOS by default ◦ Flash memory is not erased when the router is reloaded ◦ It is EEPROM (electronically erasable programmable read-only memory) NVRAM (nonvolatile RAM) ◦ Used to hold the router and switch configuration ◦ NVRAM is not erased when the router or switch is reloaded. Cisco Router Components Configuration register ◦ The configuration register is stored in NVRAM ◦ Used to control how the router boots up ◦ By default is set to 0x2102, which tells the router to load the IOS from flash memory as well as to load the configuration from NVRAM The Router Boot Sequence 1- Router performs a POST 2- Bootstrap looks for & loads the Cisco IOS 3- IOS software looks for a valid configuration file 4- Startup-config file (from NVRAM) is loaded ◦ If startup-config file is not found, the router will start the setup mode The Router Boot Sequence The Router Boot Sequence The Router Boot Sequence The Router Boot Sequence Configuration Register Register ◦ 16-bit software written into NVRAM Configuration Register Bits ◦ 16 bits read 15-0, from left to right ◦ default setting: 0x2102 Register Bit number Binary 2 15 14 13 12 0 0 1 0 1 11 10 9 8 0 0 0 1 0 7 6 5 4 0 0 0 0 2 3 2 1 0 0 0 1 0 NOTE: 0x means the digits that follow are in hexadecimal Configuration Register Bit 6 can be used to ignore the NVRAM contents (This bit is used for password recovery) The boot field, which consists of bits 0–3 in the configuration register, controls the router boot sequence Boot Field Meanings Changing the Configuration Register Force the system into the ROM monitor mode Select a boot source & default boot filename Enable or disable the Break function Set the console terminal baud rate Load operating software from ROM Enable booting from a TFTP server Changing the Configuration Register Router(config)#config-register 0x2142 Router(config)#^Z Router#sh ver Configuration register is 0x2102 (will be 0x2142 at next reload) Recovering Passwords 1- Boot the router & interrupt the boot sequence by performing a break 2- Change the configuration register to turn on bit 6 (0x2142) 3- Reload the router 4- Enter the privileged mode 5- Copy the startup-config to running-config 6- Change the password 7- Reset the configuration register to the default value 8- Reload the router Cisco IOS Programs There are two methods to connect a PC to a network device to perform configuration and monitoring tasks: ◦ out-of-band management ◦ in-band management. Cisco IOS Programs Out-of-band Management ◦ Out-of-band management requires a computer to be directly connected to the console port or auxiliary port (AUX) of the network device being configured. ◦ This type of connection does not require the local network connections on the device to be active. ◦ Technicians use out-of-band management to initially configure a network device, because until properly configured, the device cannot participate in the network. Cisco IOS Programs Out-of-band Management ◦ Out-of-band management is also useful when the network connectivity is not functioning correctly and the device cannot be reached over the network. ◦ Performing out-of-band management tasks requires a terminal emulation client installed on the PC. Cisco IOS Programs In-band Management ◦ Use in-band management to monitor and make configuration changes to a network device over a network connection. ◦ For a computer to connect to the device and perform in-band management tasks, at least one network interface on the device must be connected to the network and be operational. Cisco IOS Programs In-band Management ◦ Either Telnet, HTTP or SSH can be used to access a Cisco device for in-band management. ◦ A web browser or a Telnet client program can be used to monitor the network device or make configuration changes. Cisco IOS Programs Cisco IOS Programs The Cisco IOS command line interface (CLI) is a text-based program that enables entering and executing Cisco IOS commands to configure, monitor, and maintain Cisco devices. The Cisco CLI can be used with either in-band or out-of-band management tasks. Cisco IOS Programs Use CLI commands to alter the configuration of the device and to display the current status of processes on the router. For experienced users, the CLI offers many timesaving features for creating both simple and complex configurations. Almost all Cisco networking devices use a similar CLI. When the router has completed the power-up sequence, and the Router> prompt appears, the CLI can be used to enter Cisco IOS commands. Cisco IOS Programs In addition to the Cisco IOS CLI, other tools are available to assist in configuring a Cisco router or ISR. Security Device Manager (SDM) is a web-based GUI device management tool. Unlike CLI, SDM can be used only for in-band management tasks. Routing Basics A router uses a routing table to determine where to send packets. The routing table contains a set of routes. Each route describes which gateway or interface the router uses to reach a specified network. A route has four main components: ◦ ◦ ◦ ◦ Destination value Subnet mask Gateway or interface address Route cost or metric Routing Basics When a router receives a packet, the router examines the destination IP address in that packet to determine where to forward the packet. The router then looks for a matching destination value in the routing table. Routing Basics On a Cisco router, the Cisco IOS command show ip route displays the routes in the routing table. Several types of routes can appear in the routing table. ◦ ◦ ◦ ◦ Directly Connected Routes Static Routes Dynamically Updated Routes (Dynamic Routes) Default Route Routing Basics IP Routing process IP Routing process Routes to Directly Connected Subnets A router automatically adds a route to its routing table for the subnet connected to each interface Configuring an Interface There are different types of interfaces on a router. Serial and Ethernet interfaces are the most common. Local network connections use Ethernet interfaces. WAN connections require a serial connection through an ISP. Configuring an Interface Configuring an Interface Secondary IP Addressing Secondary IP Addressing ISL and 802.1Q Configuration on Routers ISL and 802.1Q Configuration on Routers ISL and 802.1Q Configuration on Routers Static Routes Configuring Static Routes ◦ Enter global configuration mode. ◦ Use the ip route Cisco IOS command to configure the static route, with the following format. ◦ ip route [destination_network] [subnet_mask] [gateway_address] Or ip route [destination_network] [subnet_mask] [exit_interface] Static Routes Configuring Static Routes Static Routes Configuring Static Routes Static Routes Static Routes Static Routes Static Routes Static Routes Static Default Routes Static Default Routes Classful and Classless Routing Classful and Classless Routing Classful and Classless Routing Classful and Classless Routing Dynamic Routing Dynamic routing is when protocols are used to find networks and update routing tables on routers. Dynamic routing makes it possible to avoid the time-consuming process of configuring static routes. Dynamic routing use more CPU processing and network bandwidth than static routing Routing protocol A set of messages, rules, and algorithms used by routers for the overall purpose of learning routes. This process includes the exchange and analysis of routing information. Each router chooses the best route to each subnet (path selection) and finally places those best routes in its IP routing table. Examples include RIP,EIGRP, OSPF, and BGP. Routed protocol A protocol that defines a packet structure and logical addressing, allowing routers to forward or route the packets. Routers forward, or route, packets defined by routed protocols. Examples include IP and IPX (a part of the Novell NetWare protocol model). Routing Protocol Functions 1. Learn routing information about IP subnets from other neighboring routers. 2. Advertise routing information about IP subnets to other neighboring routers. 3. If more than one possible route exists to reach one subnet, pick the best route based on a metric. 4. If the network topology changes—for example, a link fails—react by advertising that some routes have failed, and pick a new currently best route. (This process is called convergence.) Routing Protocol Functions convergence might occur if the link between R1 and R2 failed. In that case, R1 should stop using its old route for subnet 172.16.3.0/24 (directly through R2), instead sending packets to R3. Interior and Exterior Routing Protocols IGP ◦ Interior Gateway Routing Protocol ◦ Exchange routing information between routers in the same autonomous system AS ◦ Example: RIP, OSPF, and EIGRP EGP ◦ Exterior Gateway Routing Protocol ◦ Designed for use between different autonomous systems ◦ EGP is used to exchange routes between routers in different autonomous systems ◦ Example: BGP Autonomous system (AS) An AS is an internetwork under the administrative control of a single organization. Each AS is identified by a unique AS number (ASN). ASNs are controlled and registered on the Internet. Interior and Exterior Routing Protocols Classful Routing Protocols Classful routing protocols do not include the subnet mask with the route advertisement ◦ Within the same network, consistency of the subnet masks is assumed. ◦ Summary routes are exchanged between foreign networks. ◦ Examples of classful routing protocols: RIP Version 1 (RIPv1) IGRP Classless Routing Protocols Classless routing protocols include the subnet mask with the route advertisement ◦ Classless routing protocols support variablelength subnet masking (VLSM). ◦ Summary routes can be manually controlled within the network. ◦ Examples of classless routing protocols: RIP Version 2 (RIPv2) EIGRP OSPF Metric Assigns a cost to each available route so that the most cost-effective path can be chosen Routing protocols choose the best route to reach a subnet by choosing the route with the lowest metric. Metric Each routing protocol uses different metrics. The metric used by one routing protocol is not comparable to the metric used by another routing protocol. Two routing protocols might choose different paths to the same destination because they use different metrics. For example, RIP chooses the path with the fewest number of hops, whereas EIGRP chooses the path based on the highest bandwidth and least delay. Metric Metric Administrative Distance It is possible to have more than one routing protocol enabled on a single router. Additionally, a network administrator may choose to configure static routes to a specific destination. If a router has two different paths to a destination based on two different routing protocols and their metrics, how does the router know which path to use? Administrative Distance The router uses what is known as the administrative distance (AD). The AD represents the "trustworthiness" of the route. The lower the AD, the more the trustworthy the route. Integer value from 0 to 255 0 used for the most trusted Administrative Distance Routing Protocols Classes Three main branches of routing protocol algorithms exist for IGP routing protocols: ◦ Distance vector ◦ Link-state ◦ Balanced hybrid Distance Vector Concepts Routers add directly connected subnets to their routing tables, even without a routing protocol. Routers send routing updates out their interfaces to advertise the routes that this router already knows. These routes include directly connected routes, as well as routes learned from other routers. Distance Vector Concepts Routers listen for routing updates from their neighbors so that they can learn new routes. The routing information includes the subnet number and a metric. The metric defines how good the route is; lower metric routes are considered better routes. Distance Vector Concepts Routers use broadcasts or multicasts to send routing updates. If a router learns multiple routes to the same subnet, it chooses the best route based on the metric. Routers send periodic updates and expect to receive periodic updates from neighboring routers. Distance Vector Concepts Failure to receive updates from a neighbor in a timely manner results in the removal of the routes previously learned from that neighbor. A router assumes that, for a route advertised by Router X, the next-hop router in that route is Router X. Distance Vector Concepts The term distance vector describes what a router knows about each route. At the end of the process, when a router learns about a route to a subnet, all the router knows is: ◦ Measurement of distance (the metric) ◦ The next-hop router and outgoing interface to use for that route (a vector, or direction). Distance Vector Concepts Distance Vector Concepts Distance Vector Operation in a Stable Network Routing Loops The slow convergence of distance vector routing protocols can result in ◦ inconsistent routing tables ◦ routing loops. Routing loops can occur because every router isn’t updated simultaneously Route Poisoning Distance vector protocols spread the bad news about a route failure by poisoning the route. Route poisoning refers to the practice of advertising a route, but with a special metric value called infinity. Routers consider routes advertised with an infinite metric to have failed. Route Poisoning Route Poisoning Counting to Infinity Problem Counting to Infinity Problem Split Horizon In routing updates sent out interface X, do not include routing information about routes that refer to interface X as the outgoing interface. Split horizon means that when router R1 learns a route from router R2, R1 has no need to advertise that same route back to router R2. Split Horizon Poison Reverse and Triggered Updates Distance vector protocols ensures that every router learns that the route has failed as quickly as possible. ◦ Triggered update: When a route fails, do not wait for the next periodic update. Instead, send an immediate triggered update listing the poisoned route. ◦ Poison reverse: When learning of a failed route, suspend split-horizon rules for that route, and advertise a poisoned route. Poison Reverse and Triggered Updates Counting to Infinity in a Redundant Network Counting to Infinity in a Redundant Network Holddown Timer After hearing a poisoned route, start a holddown timer for that one route. Until the timer expires, do not believe any other routing information about the failed route, because believing that information may cause a routing loop. However, information learned from the neighbor that originally advertised the working route can be believed before the holddown timer expires. Holddown Timer RIP Routing Information Protocol Use hop count as metric Can load balance up to 6 equal cost paths (default = 4) Maximum hop count 15 RIPv1 use default subnet mask (classful) RIPv2 supports VLSM and Discontiguous networks RIP Timers Route Update Timer ◦ 30 seconds Route Invalid Timer ◦ 90 seconds Hold-down Timer ◦ 180 seconds Route Flush Timer ◦ 240 seconds ◦ Remove the route from the routing table Configuring RIP Routing Router(config)#router rip Router(config-router)#network network-number* 10.3.5.0 172.16.10.0 router RIP router RIP network 172.16.0.0 network 10.0.0.0 network 172.16.0.0 network 192.168.10.0 *Network is a classful network address. Passive Interface Maybe you don’t want to send RIP updates out your router interface connected to the Internet. Use the passive-interface command: Router(config)#router rip Router(config-router)#passive-interface serial0 Internet X S0 Updates Gateway This allows a router to receive route updates on an interface, but not send updates via that interface RIP version 1 Example 1 RIP Version 2 Allows the use of variable length subnet masks (VLSM) by sending subnet mask information with each route update Distance Vector – same AD, and timers. Easy configuration, just add the command “version 2” under the router rip configuration router rip network 10.0.0.0 version 2 Discontiguous Addressing Two networks of the same classful networks are separated by a different network address 172.16.10.0/24 172.16.11.0/24 10.1.1.0/24 – RIPv1 and IGRP do not advertise subnet masks, and therefore cannot support discontiguous subnets. – OSPF, EIGRP, and RIPv2 can advertise subnet masks, and therefore can support discontiguous subnets. RIPv1 vs. RIPv2 Verifying RIP Router#show ip route Router#show ip protocols Router#debug ip rip Router#undebug all Verifying RIP Verifying RIP R1# show ip protocols Verifying RIP IGRP Interior Gateway Routing Protocol Cisco proprietary Use bandwidth and delay as default composite metric Can use also another metrics as load, reliability and MTU Load balance up to 6 routes (default = 4) Use bandwidth to determine how to load balance between routes (not equal cost) IGRP Timers Route Update Timer ◦ 90 seconds Route Invalid Timer ◦ 3 * 90 seconds Hold-down Timer ◦ 3 * 90 + 10 seconds Route Flush Timer ◦ 7 * 90 seconds ◦ Remove the route from the routing table IGRP vs. RIP Thank you