Quick Notes – IOS COMMANDS

Posted by on July 13, 2010 No comments | 2,148 views

What two EXEC modes are supported in the Cisco IOS?

The two EXEC modes are:

  • User EXEC mode (user mode)
  • Privileged EXEC mode (enable or privileged mode)

In the IOS, what is User EXEC mode?

User EXEC mode is the first mode you enter when you log into the IOS. This mode is limited and is mostly used to view statistics. You cannot change a router’s configuration in this mode. By default, the greater-than sign (>) indicates that you are in user mode. This is how the router prompt looks in user mode: Router>

In the IOS, what is privileged EXEC mode?
In privileged EXEC mode, you can view and change the configuration in a router. To enter privileged mode, enter the enable command while in user mode. The pound symbol (#) indicates that you are in privileged mode. This mode is usually protected with a password. You also see the output of the prompt:

Router>enable
Password:
Router#

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OSPF Summary

Posted by on July 12, 2010 No comments | 930 views

The characteristics of OSPF follow

  • Link-state routing protocol.
  • Uses IP protocol 89.
  • Classless protocol (supports VLSMs and CIDR).
  • Metric is cost, based on interface bandwidth by default (10^8 / BW in bps).
  • Sends partial route updates only when there are changes.
  • Send hello packets every 10 sec with dead timer of 40 sec over P-P & BC networks.
  • Send hello packets every 30 sec with dead timer of 120 sec over NBMA networks.
  • If the network is stable and there have been no updates within 30 min, a compressed update is sent.
  • Routes labeled as intra-area, interarea, external Type 1, or external Type 2.
  • Support for authentication.
  • Uses Dijkstra algorithm to calculate SPF tree.
  • Default administrative distance is 110.
  • Uses multicast address 224.0.0.5 (ALLSPFRouters).
  • Uses multicast address 224.0.0.6 (ALLDRouters).
  • Recommended for large networks.
  • For 2 routers to be adjacent :
    • 1st. Hello packets must be sent & received.
    • 2nd They must have the same hello & dead timers Also & same Net ID with subnet mask.
    • 3rd They must be in the same area.

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RIPv2 Summary

Posted by on July 11, 2010 No comments | 1,016 views

The characteristics of RIPv2 follow:

  • Distance-vector protocol.
  • Use UDP port 520.
  • Makes Automatic summarization on network Class boundary.
  • Classless protocol (supports VLSMs).
  • Have the power to shut the Auto-summarization And make a configured manual Summarization.
  • Supports VLSMs.
  • Metric is router hop count.
  • Maximum hop count is 15; infinite (unreachable) routes have a metric of 16.
  • Periodic route updates sent every 30 seconds to multicast address 224.0.0.9.
  • 25 routes per RIP message (24 if authentication is used).
  • Invalid route marked after 180 sec.
  • Flush timer is 280 sec.
  • Hold-down timer 180 sec.
  • Supports authentication.
  • Implements split horizon with poison reverse.
  • Implements triggered updates.
  • Subnet mask included in route entry.
  • Administrative distance for RIPv2 is 120.
  • Used in small, flat networks or at the edge of larger networks.

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EIGRP Summary

Posted by on July 11, 2010 No comments | 2,483 views

The characteristics of EIGRP follow:

  • Hybrid routing protocol (distance vector that has link-state protocol characteristics).
  • Use DUAL, first proposed by E. W. Dijkstra and C. S. Scholten, to perform distributed shortest-path routing while maintaining freedom from loops at every instant. Although many researchers have contributed to the development of DUAL, the most prominent work is that of J. J. Garcia-Luna-Aceves.
  • Cisco Proprietary created in 1994.
  • First released in IOS 9.21
  • Uses IP protocol 88.
  • Makes Automatic summarization on network Class boundary.
  • Classless protocol (supports VLSM).
  • Have the power to shut the Auto-summarization And make a configured manual Summarization.
  • Default composite metric of bandwidth and delay.
  • You can factor load, MTU and reliability into the metric.
  • Eigrp metric is the same as IGRP*256, It uses the smallest B.W,Reliablity,Load & MTU with the Comulative delay upon the path…..The MTU doesn’t actually used in the Metric calculations, But is included in the EIGRP Routing updates.
  • Sends route updates to multicast address 224.0.0.10, and nei. Reply’s back with Unicast Address.
  • Sends non-periodic, partial, and bounded updates.
  • Send Hello packets every 5 sec. and Hold down timer is 15 sec.
  • For Low speed Hello is every 60 sec. with hold down time 180 sec.
  • By default, EIGRP uses no more than 50 percent of the bandwidth of a link.
  • Support for authentication via MD5 Only.
  • Uses DUAL for loop prevention, and generating Succ./Fesible Succ.
  • Maximum paths for Load-balancing are 6 & default is 4 , maximum are 16 in IOS 12.3(2)T and later IOS releases
  • By default, Equal-Metric load balancing. If Unequal-Metric load sharing is used the router will load share inversely proportional to the metrics of the paths.
  • Administrative distance is 90 for EIGRP internal routes, 170 for EIGRP external routes, and 5 for EIGRP summary routes.
  • Potential routing protocol for the core of a network; used in large networks.
  • For neighbor relation to be established, both routers must send and receive Hello or Ack packets from each other, they must have the same AS #, and the same Metric K values.
  • Eigrp doesn’t restrict that neighbors must have the same Hello & dead interval timers, Unlike OSPF.
  • Has a Maximum hop count of 255, the default is 100 in the last IOS releases.

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OSPF Basics

Posted by on July 11, 2010 No comments | 890 views

Introduction

The Open Short Path First (OSPF) is defined in RFC 2328.It is an interior Gateway Protocol used to distribute routing information within a single Autonomous system. It is a most common routing protocol using by Service Providers, because unlike EIGRP it is an Open Standard protocol.

Why we are calling OSPF is a link state routing protocol. Unlike RIP, OSPF is not only sending the Routing updates to its neighbors. It is sending all the information about the link like IP address of the Interface and subnet mask, the type of network it is connected to (P2P or P2Multi-point or FR) and the routers which is connected to it. The collection of these link states will form a Link state Database.

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Configuring a Router

Posted by on July 7, 2010 No comments | 1,002 views

Router Modes

Router> User mode
Router# Privileged mode
Router(config)# Global configuration mode
Router(config-if)# Interface mode
Router(config-subif)# Subinterface mode
Router(config-line)# Line mode
Router(config-router)# Router configuration mode

Global Configuration Mode

Router> Can see config, but not change
Router# Can see config and move to make changes
Router#config t Moves to global config mode
Router(config)# This prompt indicates that you can start making changes

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Distance Vector and Link State Routing Protocol

Posted by on July 1, 2010 No comments | 1,304 views

There are two major differences between Distance Vector routing protocols and Link State routing protocols. Distance Vector exchanges the routing updates periodically whether the topology is change or not, this will maximize the convergence time which increases the chance of routing loops while the Link State routing protocols send triggered change based updates when there is a topology change. After initial flood, pass small event based triggered link state updates to all other routers. This will minimize the convergence time that’s why there is no chance of routing loops. Secondly, the Distance Vector routing protocols rely on the information from their directly connected neighbours in order to calculate and accumulate route information. Distance Vector routing protocols require very little overhead as compared to Link State routing protocols as measured by memory and processor power while the Link State routing protocols do not rely solely on the information from the neighbours or adjacent router in order to calculate route information. Instead, Link State routing protocols have a system of databases that they use in order to calculate the best route to destinations in the network. An extra feature of Link State routing protocol is that they can detect media types along with other factors. This could increase the overhead as compare to Distance Vector routing protocols in order to measure by processor power and memory. Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP) are the examples of Distance Vector routing protocols while the Open Shortest Path First (OSPF) is a classic example of Link State routing protocols.

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RIPv2 – Things to Remember

Posted by on June 25, 2010 No comments | 849 views

1. The RIP process operates from UDP port 520.

2. The metric used by RIP is hop count, with 1 signifying a directly connected network of the advertising router and 16 signifying an unreachable network.

3. RIP sends periodic updates every 30 seconds minus a small random variable that prevents the updates of neighboring routers from becoming synchronized.

4. Default route can be advertised in the RIP domain several ways: e.g. (1) static route to 0.0.0.0, with the “redistribute static” command, (2) “default-information originate” command, and (3) “ip default-network” command.
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Static Routing Tutorial

Posted by on June 20, 2010 No comments | 1,006 views

In studying for your CCNA exam and preparing to earn this valuable certification, you may be tempted to spend little time studying static routing and head right for the more exciting dynamic routing protocols like RIP, EIGRP, and OSPF.

This is an understandable mistake, but still a mistake. Static routing is not complicated, but it’s an important topic on the CCNA exam and a valuable skill for real-world networking.

To create static routes on a Cisco router, you use the ip route command followed by the destination network, network mask, and either the next-hop IP address or the local exit interface. It’s vital to keep that last part in mind – you’re either configuring the IP address of the downstream router, or the interface on the local router that will serve as the exit interface.

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Static Routing

Posted by on June 20, 2010 No comments | 3,796 views
Static Routing
Static routing is the term used to refer to a manual method that is used to set up routing between networks. The network administrator configures static routes in a router by entering routes directly into the routing table of a router. Static routing has the advantage of being predictable and simple to set up. It is easy to manage in small networks but does not scale well. Compare this with dynamic routing. Read more »
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