ICND 1 (CCENT) Section 13

ARP (Address Resolution Protocol)

A layer 2 protocol that is used to map an IP address to a MAC address. Defined in RFC 826.

Default gateway

A router interface that is connected to a local network that has a network layer address that matches the network address of the hosts. Hosts are also configured to recognize that network address.

Telnet

A standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log into remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854.

"ipconfig" utility

A utility that is ran from the Windows command prompt. This utility allows you to get the IP address information of a Windows computer.

What happens when you ping the local host during toubleshooting?

If the ping is successful, your NIC is functioning. If it fails, there is a problem with the NIC. If the ping is successful, it does not mean that a cable is plugged into the NIC, but only that the IP protocol stack on the host can communicate to the NIC (via the LAN driver).

What happens when you ping the default gateway during toubleshooting?

If the ping works, it means that the NIC is plugged into the network and can communicate on the local network. If it fails, you have a local physical network problem that could be anywhere from the NIC to the router.

What happens when you ping a loopback address during toubleshooting?

If you get a successful ping, your IP stack is considered to be initialized. If it fails, you have an IP stack failure, and you need to reinstall TCP/IP on the host.

What services does ARP provide?

- Address resolution: Mapping IP addresses to MAC addresses on a network - Caching: Locally storing MAC addresses that are learned via ARP

What are the four recommended troubleshooting steps that you should perform from the host?

1. Ping the loopback address. 2. Ping the local host. 3. Ping the default gateway. 4. Ping the remote server.

ICMP(Internet Control Message Protocol)

A Network layer Internet protocol that reports errors and provides other information that is relevant to IP packet processing. Documented in RFC 792.

SSH (Secure Shell Protocol)

A Protocol that provides a secure remote connection to a route through a TCP application.

"Traceroute"

A command that can return useful information about TCP/IP connectivity across your network. IT sends out either ICMP echo request (Microsoft Windows) or UDP (most implementations) messages with gradually increasing IP TTL values to probe the path by which a packet traverses the network.

"Tracert"

A command that is the same as Traceroute, but it is a Windows command and will not work on a Cisco router.

"Ping" Command

A command that uses the IP ICMP echo request and echo reply messages to test reachability to a remote system. It simply confirms that an IP packet is capable of getting to and getting back from a destination IP address. It generally returns two pieces of information: whether the source can reach the destination (and, by inference, vice versa) and the RTT

" Show IP ARP" command

A command used to display the ARP table on a Cisco IOS router. (Must be in EXEC mode to execute)

"arp -a" command

A command used to displays the current ARP table for all interfaces on a PC using the Microsoft Windows operating system.

"(arp -a -N) (ip_address)" command

A command used to limit the output of the arp command to a single interface

telnet "EXEC" command

A command used to log on to a host that supports Telnet

SSH user "EXEC" command

A command used to start an encrypted session with a remote networking device.

(ARP Table) Cache

Contains an ARP table whose purpose is to cache recent IP addresses and MAC address bindings. When a host wants to transmit data to another host on the same network, it searches the ARP table to see if there is an entry. If there is an entry, the host uses it. If there is no entry, the IP host sends an ARP broadcast requesting resolution.

mac-address (ARP table syntax)

Displays 48-bit MAC address

ip-address (ARP table syntax)

Displays ARP entries matching this IP address

interface type number (ARP table syntax)

Displays ARP entries that are learned via this interface type and number

host-name (ARP table syntax)

Displays hostname

DOS (Disk Operating System)

The original operating system for the PC from Microsoft Corporation

(ARP) Address resolution (Where you at?)

The process of binding the IP address of a remote device to its MAC address. ARP sends a broadcast message to all devices on the local network. This message includes its own IP address and the destination IP address. The message is basically asking the device on which the destination IP address resides to respond with its MAC address.

"ipconfig" /all utility

This utility option displays the IP address, network mask, and gateway for all physical and virtual network adapters. Also, it displays DNS and WINS settings for each adapter.

WINS

Windows Internet Name Service

What is the proper syntax to display the ARP table?

show ip arp [ip-address], [host-name], [mac-address] ,[interface type number].