IOS Commands

Privileged Mode

   enable - get to privileged mode

   disable - get to user mode

Configuring the Router

   sh running-config - details the running configuration file (RAM)

   sh startup-config - displays the configuration stored in NVRAM

   setup - Will start the the automatic setup; the same as when you first boot the router

   config t - use to execute configuration commands from the terminal

   config mem - executes configuration commands stored in NVRAM; copies startup-config to running-config

   config net - used to retrieve configuration info from a TFTP server

   copy running-config startup-config - copies saved config in running config (RAM) to NVRAM or "write memory" for IOS under ver.11

   copy startup-config running-config - copies from non-volatile (NVRAM) to current running config (RAM)

   boot system flash <filename_here> - tells router which IOS file in flash to boot from

   boot system tftp - tells router which IOS file on the tftp server to boot from

   boot system rom - tell router to boot from ROM at next boot

   copy flash tftp - Copies flash to tftp server

   copy tftp flash - Restores flash from tftp server

   copy run tftp - Copies the current running-config to tftp server

   copy tftp run - Restores the running-config from tftp server

General Commands

   no shutdown - (enables the interface)

   reload - restarts the router

   sh ver - Cisco IOS version, uptime of router, how the router started, where system was loaded from, the interfaces the POST found, and the configuration register

   sh clock - shows date and time on router

   sh history - shows the history of your commands

   sh debug - shows all debugging that is currently enabled

   no debug all - turns off all debugging

   sh users - shows users connected to router

   sh protocols - shows which protocols are configured

   banner motd # Your_message # - Set/change banner

   hostname <router_name_here> - use to configure the hostname of the router

   clear counters  - clear interface counters

Processes & Statistics

   sh processes - shows active processes running on router

   sh process cpu - shows cpu statistics

   sh mem - shows memory statistics

   sh flash - describes the flash memory and displays the size of files and the amount of free flash memory

   sh buffers - displays statistics for router buffer pools; shows the size of the Small, Middle, Big, Very Big, Large and Huge Buffers

   sh stacks - shows reason for last reboot, monitors the stack use of processes and interrupts routines

CDP Commands (Cisco Discovery Protocol uses layer 2 multicast over a SNAP-capable link to send data):

   sh cdp neighbor - shows directly connected neighbors

   sh cdp int - shows which interfaces are running CDP

   sh cdp int eth 0/0 - show CDP info for specific interface

   sh cdp entry <cdp_neighbor_here> - shows CDP neighbor detail

   cdp timer 120 - change how often CDP info is sent (default cdp timer is 60)

   cp holdtime 240 - how long to wait before removing a CDP neighbor (default CDP holdtime is 180)

   sh cdp run - shows if CDP turned on

   no cdp run - turns off CDP for entire router (global config)

   no cdp enable - turns off CDP on specific interface

Miscellaneous Commands

   sh controller t1  - shows status of T1 lines

   sh controller serial 1 - use to determine if DCE or DTE device

   (config-if)#clock rate 6400 - set clock on DCE (bits per second)

   (config-if)#bandwidth 64 - set bandwidth (kilobits)

IP Commands

Configure IP on an interface:

    int serial 0

    ip address 157.89.1.3 255.255.0.0

    int eth 0

    ip address 2008.1.1.4 255.255.255.0

Other IP Commands:

    sh ip route - view ip routing table

    ip route <remote_network> <mask> <default_gateway> [administrative_distance] - configure a static IP route

    ip route 0.0.0.0 0.0.0.0 <gateway_of_last_resort> - sets default gateway

    ip classless - use with static routing to allow packets destined for unrecognized subnets to use the best possible route

    sh arp - view arp cache; shows MAC address of connected routers

    ip address 2.2.2.2 255.255.255.0 secondary - configure a 2nd ip address on an interface

    sh ip protocol

Routing Protocols

Configure RIP:

    router rip

    network 157.89.0.0

    network 208.1.1.0

Other RIP Commands:

    debug ip rip - view RIP debugging info

Configure IGRP:

    router IGRP 200

    network 157.89.0.0

    network 208.1.1.0

Other IGRP Commands:

    debug ip igrp events - view IGRP debugging info

    debug ip igrp transactions - view IGRP debugging info

Access Lists (see notes below for details)

sh ip int ser 0 - use to view which IP access lists are applies to which int

sh ipx int ser 0 - use to view which IPX access lists are applies to which int

sh appletalk int ser 0 - use to view which AppleTalk access lists are applies to which int

View access lists:

    sh access-lists

    sh ip access-lists

    sh ipx access-lists

    sh appletalk access-lists

Apply standard IP access list to int eth 0:

    access-list 1 deny 200.1.1.0 0.0.0.255

    access-list 1 permit any

    int eth 0

    ip access-group 1 in

Apply Extended IP access list to int eth 0:

    access-list 100 deny tcp host 1.1.1.1 host 2.2.2.2 eq 23

    access-list 100 deny tcp 3.3.3.0 0.0.0.255 any eq 80

    int eth 0

    ip access-group 100 out

Apply Standard IPX access list to int eth 0:

   access-list 800 deny 7a 8000

    access-list 800 permit -1

    int eth 0

    ipx access-group 800 out

Apply Standard IPX access list to int eth 0:

    access-list 900 deny sap any 3378 -1

    access-list 900 permit sap any all -1

    int eth 0

    ipx access-group 900 out

 

Wan Configurations (see notes below for more details)

PPP Configuration

   encapsulation ppp

   ppp authentication <chap_or_pap_here>

   ppp chap hostname <routername_here>

   ppp pap sent-username <username_here>

   sh int ser 0 - use to view encapsulation on the interface

Frame-Relay Configuration

   encapsulation frame-relay ietf - use IETF when setting up a frame-relay network between a Cisco router and a non-Cisco router

   frame-relay lmi-type ansi - LMI types are Cisco, ANSI, Q933A; Cisco is the default; LMI type is auto-sensed in IOS v11.2 and up

   frame-relay map ip 3.3.3.3 100 broadcast - if inverse ARP won't work, map Other IP to Your DLCI # (local)

   keepalive 10 - use to set keepalive

   sh int ser 0 - use to show DLCI, LMI, and encapsulation info

   sh frame-relay pvc - shows the configured DLCI's; shows PVC traffic stats

   sh frame-relay map - shows route maps

   sh frame-relay lmi - shows LMI info

Keyboard Shortcuts

   CTRL-P - show previous command

   CTRL-N - show next command

   SHIFT-CTRL-6 - Break

Notes  

Static and Dynamic Routing

Static Routing - manually assigned by the Admin user entering the routes (Routed Protocols - IP, IPX and AppleTalk)

Dynamic Routing - generated/determined by a Routing Protocol (Routing Protocols - RIP I, RIP II, IGRP, EIGRP, OSPF, NLSP, RTMP) Dynamic

     1) With Dynamic Routing, routers pass information between each other so that routing tables are regularly maintained.

     2) The routers then determine the correct paths packets should take to reach their destinations.

     3) Information is passed only between routers.

     4) A routing domain is called an Autonomous System, as it is a portion of the Internetwork under common admin authority.

     5) Consists of routers that share information over the same protocol. Can be split into routing areas. 

 

Distance Vector and Link-State Routing

Routing Protocols

     I) Interior (within an autonomous system - AS - group of routers under the same administrative authority)

      a) Distance Vector - understands the direction and distance to any network connection on the internetwork. Knows how

    many hops (the metric) to get there. All routers w/in the internetwork listen for messages from other routers, which are sent

    every 30 to 90 seconds. They pass their entire routing tables. Uses hop count for measurement. 1) Used in smaller networks

    that are have fewer than 100 routers.  2) Easy to configure and use.  3) As routers increase in number, you need to consider

    CPU utilization, convergence time, and bandwidth utilization.  4) Convergence is due to routing updates at set intervals.  5) When

    a router recognizes a change it updates the routing table and sends the whole table to all of its neighbors.

            1) RIP - 15 hop count max

            2) IGRP - 255 hop count max, uses reliability factor (255 optimal), and bandwidth

            3) RTMP

      b) Link State - understands the entire network, and does not use secondhand information. Routers exchange LSP?s (hello packets). Each router builds a topographical view of the network, then uses SPF (shortest path first) algorithm to determine the best route. Changes in topology can be sent out immediately, so convergence can be quicker. Uses Bandwidth, congestion for measurement; Dijkstra's algorithm;

         1) Maintains Topology Database. 
         2) Routers have formal neighbor relationship.
         3) Exchanges LSA (Link State Advertisement) or hello packets with directly connected interfaces.
         4) These are exchanged at short intervals (typically 10 sec).
         5) Only new info is exchanged.
         6) Scales well, however link?state protocols are more complex.
         7) Requires more processing power, memory, and bandwidth.

              1) OSPF - decisions based on cost of route (metric limit of 65,535)

              2) EIGRP - hybrid protocol (both Distance-Vector and Link State), Cisco proprietary

              3) NLSP

              4) IS-IS

II) Exterior

            1) EGP (Exterior Gateway Protocol)

            2) BGP (Border Gateway Protocol) 

Routing Protocols used for each Routed Protocol

IP - RIP, IGRP, OSPF, IS-IS, EIGRP

IPX - IPX RIP, NLSP, EIGRP

AppleTalk - RTMP, AURP, EIGRP

Problems with Routing Protocols

   1) Routing Loops - occur when routing tables are not updated fast enough when one of the networks becomes unreachable. Due to the slow convergence (updates of routing table between all routers), some routers will end up with incorrect routing table and will broadcast that routing table to other routers. This incorrect routing tables will cause packets to travel repeatedly in circles.

   2) Counting to infinity - occurs when packets end up in a routing loop; hop count increases with every pass through a router on the network

Solutions to Problems with Routing Protocols

   1) Define the maximum number of hops - When the number of hops reaches this predefined value, the distance is considered infinite, thus the network is considered unreachable. This does stop routing loops, but only limit the time that packet can travel inside the loop.

   2) Split horizon - The packets can not be sent back to the same interface that they originally came from. During the updates, one router does not send updates to the router that it received the information from.

   3) Route poisoning - The router sets the cost/distance of routes that are unreachable to infinity.  Used with hold-down timers

   4) Triggered updates - The router sends updates of the routing table as soon as it detects changes in the network.  Does not wait for the prescribed time to expire.

   5) Hold-Downs - After the router detects  unreachable network, the routers waits for a specified time before announcing that a network is unreachable. The router will also wait for a period of time before it updates its routing table after it detects that another router came online (Router keeps an entry for the network possibly down state, allowing time for other routers to re-compute for this topology change).  Hold-downs can only partially prevent counting to infinity problem. Prevents routes from changing too rapidly in order to determine if a link has really failed, or is back up