Thursday, November 24, 2011

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
    int eth 0
    ip address 2008.1.1.4
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 <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 secondary - configure a 2nd ip address on an interface
    sh ip protocol

Routing Protocols
Configure RIP:
    router rip
Other RIP Commands:
    debug ip rip - view RIP debugging info
Configure IGRP:
    router IGRP 200
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
    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 host eq 23
    access-list 100 deny tcp 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 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

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 
         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

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


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