Cisco® ROUTERS STARTUP SEQUENCE
ROM Load Bootstrap
Flash TFTP Locate & load operating system ROM
NVRAM Locate & load configuration file TFTP Server or enter "setup" mode Console
1. The bootstrap program is stored in and executed from ROM on the CPU card 2. The operating system source is determined from the boot field setting in the router's configuration register. Flash memory is the default. Once a valid Cisco® IOS image is loaded, it then searches for a configuration file 3. The operating system image is loaded into low-addressed memory 4. The saved configuration file in NVRAM is then loaded into main memory and executed one line at a time 5. If no valid configuration exists in NVRAM, the operating system will respond by deploying a "question-driven initial configuration dialog," referred to as the system configuration dialog (setup dialog) THE USER INTERFACE User Mode * To check the router's status * Make temporary changes to terminal settings * View basic system information Privileged Mode * All those in user mode, plus * Setting operating system parameters * Get detailed information on router's status * Test and debug operations * Access global configuration modes
Cisco® ROUTERS Logging In Router> Exec Mode Prompt To exit from user mode type logout To enter privileged mode: Router>enable Password: (not shown) To exit from privileged mode and return to user mode type disable
To leave either mode and logout type exit or quit Help If you need to set the clock but don't know the commands type Router#clock ? Editing Commands CTRL+A Move to the beginning of the command line CTRL+E Move to the end of the command line CTRL+F Move forward one character CTRL+B Move back one character CTRL+P Repeat previous command entry CTRL+N Most recent command recall ESC+B Move back one word Esc+F Move forward one word Router> show history Show command buffer Router> terminal history size Set command buffer size Tab Completes entry for you
show startup-config to see the configuration in NVRAM config t changes amend this file in DRAM the type Router#copy running-config startup-config
Cisco® ROUTERS Passwords Enable Secret - a one-way cryptographic secret password for versions 10.3 and up Router#config t Router(config)#enable secret _______ Router(config)#^Z Enable Password - when there is no secret password with older versions Router#config t Router(config)#enable password _______ Router(config)#^Z Virtual Terminal Password - used for Telnet sessions into the router Router#config t Router(config)#line vty 0 4 Router(config-line)#login Router(config-line)#password ________ Router(config)#^Z Auxiliary Password - to set a password for the auxiliary port Router#config t Router(config)#line aux 0 Router(config-line)#login Router(config-line)#password ________ Router(config)#^Z Console Password - to set the console port password Router#config t Router(config)#line con 0 Router(config-line)#login Router(config-line)#password ________ Router(config)#^Z Banners * Must be started with a delimiting character Router(config)#banner motd # Enter TEXT message. End with the character '#'. Mind your business! # [enter] Hostnames * Changes the name of your router Router#config t Router(config)#hostname RouterC RouterC(config-line)#^Z
Cisco® ROUTERS Shutdown shutdown turns the administrative state of the interface down no shutdown turns the administrative state of the interface up Switch and VIP Interfaces * Modular devices, Catalyst 5000, number their interfaces using the syntax type slot/port (e 4/2 for Ethernet card 4, port 2) * Cisco® 7000 and 7500 have Versatile Interface Processor (VIP) cards and have one or two slots per port adapter and each port adapter can have a number of interfaces so their interfaces use the syntax type slot/port adapter/port * Configuring a port on the third Ethernet VIP card, first port (0), second Ethernet interface type e 2/0/1 DTE/DCE Cable * By default Cisco® routers are DTE devices, but when you have routers connected together (WAN link) you can define a serial interface as a DCE device * Because we don't have a CSU/DSU to handle clocking we must add the clock rate command to the DCE serial ports on our routers * Type the command RouterC#sh controllers serial [port number] To see if the interface sees a DCE or DTE cable
ROUTING BASICS IP Routing * The process of sending data from a host on one network to a remote host on another network through a router or routers Static Routing * Requires that tables be built and updated manually * Can be configured using the ip route command line Ip route network mask address/interface [distance] where * Network destination network or subnet * Mask subnet mask * Address IP address of next hop router * Interface name of interface to use to get to destination network * Distance the administrative distance (expressed as a value from 0 to 255 with the lower the number the higher the trustworthiness Default Routing * Should be set in each router by creating a default route entry using the network and subnet mask of all 0s so that if a router doesn't know the path to a certain network it can use the default route IP Classless Command * If a router receives packets destined for a network that doesn't have a network default route, you need the ip classless global configuration command to get the Cisco® IOS to forward packets to the best route * If you are using static routing you should use the ip classless command
DYNAMIC IP ROUTING Routed Vs Routing Protocols * Routed and routing protocols practice ships-in-the-night routing because they are focused and pay no attention to each other's protocols
Routed (IP or IPX) * Used between routers to direct user traffic, specifying the type of fields and how they're used within the packet to send data from sending to destination machines Routing Protocols (RIP, OSPF, NLSP, IGRP or EIGRP) * Maintains routing tables that are used between routers Autonomous System * A portion of an internetwork under common administrative authority, routers that share information using the same routing protocol INTERIOR ROUTING PROTOCOLS A - Distance-Vector (RIP, IGRP & EIGRP) * Listens to secondhand information to get its updates and understands the direction and distance to any network connection on the internetwork * The time it takes for all routers to update their tables when a change occurs is convergence time * Update every 30 to 90 seconds causing all routers to pass their entire routing tables to all other known routers and paths are calculated by and based on the number of hops the routers are from each neighbour Routing Loops * Because every router is not updated at close to the same time when an interface fails not all routers will receive this information in their updates * Its caused by wrong information being communicated and propagated throughout the internetwork Counting to Infinity * A maximum hop count of 15 ensures that any requirement of 16 hops is deemed unreachable Split Horizon * Reduces incorrect routing information and overhead by enforcing the rule that information cannot be sent back in the direction from which it was received Route Poisoning * Speeds up convergence time because neighbouring routers don't have to wait 30 seconds before advertising the poisoned route DYNAMIC IP ROUTING Hold-Downs * Work with route poisoning to prevent regular update messages from reinstating a downed route and uses triggered updates which reset the hold-down timer to let all routers know of a change in the network Routing Information Protocol (RIP) * A distance-vector routing protocol which uses classfull routing, summarizing routing information by major network numbers, to discover the cost of a given route in terms of hops and store that information in the routing table * RIP routing tables provide: * IP destination address * A metric (1-15) indicative of hop count * IP address of the next router * A marker signaling changes to a route * Timers used to regulate performance * Flags indicating recent changes to a route * Hold-downs, split horizon and poison reverse Interior Gateway Routing Protocol (IGRP) * Proprietary to Cisco®, IGRP builds routing tables using: * Metrics (1-255) set by an administrator * Delay being the speed of the media * Bandwidth * Reliability, fractions of 255 where 255 is optimal * Multipath routing, hold-downs, split horizon and poison reverse updates * IGRP advertises three types of routes * Interior, routes between subnets * System, routes to directly connected interfaces, other IGRP routes and access servers * Exterior, routes to networks outside of the autonomous system
Enhanced Interior Gateway Routing Protocol (EIGRP) * A balanced hybrid routing protocol which employs distance vectors to determine the best paths to destination networks and uses topology changes to trigger routing database updates * EIGRP features * Fast convergence * Variable-length subnet masks * Partial bounded updates * Multiprotocol support DYNAMIC IP ROUTING B - Link State (OSPF) * Maintains in its tables a complete understanding and view of all the links of distant routers and how they interconnect by: * exchanging link state packets (LSPs) or "hello packets" with one another communicating only its directly connected links * compiling all of the LSPs received and build a topological database * using the shortest path first (SPF) algorithm computes the shortest, most efficient path to each participating link-state network * In order to converge each router in a link-state network must: * remember its neighbour's name, when it's up/down and the cost of the path to that router * create an LSP that lists its neighbour's name and relative costs * send the LSP to all other routers * receive LSPs from other routers and update its own database * build a complete topological map and compute the best route to each network destination * Routers require more power, memory and bandwidth but after the initial deluge of LSPs updates occur only every two hours unless a new router comes online or a link drops * Routers can be configured to use a designated router (DR) as the target to consult for all changes * In large internetworks routers can implement LSP time stamps, sequence numbers and aging schemes to avoid spreading misinformation Open Shortest Path First (OSPF) * Based on link-state algorithms, it's deployed within an autonomous system with each router retaining its own topological database * Network administrators are free to assign costs to a particular link * Link-state routing advertisements are broadcasted only when a change is detected * Link-state routing packets can carry information for more than one router, i.e. neighboring routers, at the same time * OSPF can receive and send routes to other autonomous systems * Additional features include Type of Service routing (TOS), support for one or more metrics and variable-length subnet masks (VLSMs) Distance-Vector vs. Link-State
Distance-Vector Link-State Topological Data Source Secondhand or net gossip Compiles LSPs Determining Best Path Counting hops Bandwidth analysis, plus Updates 30-second intervals slower convergence Triggered by topology changes Faster convergence DYNAMIC IP ROUTING Default Administrative Distances Directly Connected Interface 0 Static Route 1 External BGP (Exterior) 20 Direction Enhanced IGRP (Balanced Hybrid) 90 of IGRP (Distance-Vector, Interior) 100 Reliability OSPF (LinkState, Interior) 110 IS-IS (Balanced Hybrid) 115 RIP (Distance-Vector, Interior) 120 EGP (Distance-Vector, Exterior) 140 EXTERIOR ROUTING PROTOCOLS Exterior Gateway Protocol (EGP) * Distance-vector protocol that allows Ass to communicate through s core routing network * Routing updates specify only that certain networks are available
through certain routers * Establish a set of neighbors and test whether they are alive using polling and neighbor acquisition messages * Use neighbor reachability messages to see if neighbor is "down" * Use poll messages to acquire accessibility information about networks on which remote hosts reside * Use error messages to identify various error conditions Border Gateway Protocol (BGP) * Inter-autonomous protocol which can be used both between and within Ass and determine routing loops * Router coming online receives a complete GGP routing table from its neighbor * Updates are sent out incrementally through update messages which advertise only what is considered the best or optimal path * Other types of messages include: * Open - the first message sent after a transport protocol connection is established * Notification - the message sent when an error occurs * Keepalive - messages sent often enough to keep the hold timer from expiring
DYNAMIC IP ROUTING CONFIGURING RIP ROUTING * Take out all static and default entries in the routing tables RouterA#config t RouterA(config)#no ip route 172.16.50.0 * Connect the console cable to each router, one at a time * Add the RIP protocol in RouterA and tell the router the networks we want to advertise RouterA#config t RouterA(config)#router rip RouterA(config-router)#network 172.16.0.0 RouterA(config-router)#^Z RouterA#copy run star Passive RIP * Stops the router from sending out any updates on the specified interface RouterA#config t RouterA(config)#router rip RouterA(config)#network 172.16.0.0 RouterA(config)#passive ? Ethernet IEEE 802.3 Null Null Interface Serial Serial RouterA(config-router)#passive serial 1 RouterA(config-router)#exit CONFIGURING IGRP ROUTING * Since you can have multiple IGRP routing protocols running between the routers, you have to enter the autonomous system number RouterA#config t RouterA(config)#router igrp ? RouterA(config)#router igrp 10 RouterA(configrouter)#network 172.16.0.0 RouterA(config-router)#^Z RouterA#copy run star