[Cisco Networking Academy] Del Mar College
ITNW 1392-Beginning Router Configuration
 Instructor:Michael P. harris
Sem2Les12

Semester 2, Lesson 12 Notes:

TCP/IP Address Overview and Configuring Router Addresses

Each node using the TCP/IP protocol suite has a unique '32-bit logical address'. This address is known as the "IP address".

Each company listed on the internetwork is seen as a 'single unique network' that must be reached before an 'individual host' within that company can be contacted. Each company network has an address; the hosts that live on that network share that same "network address", but each host is identified by the unique "host address" on the network.

"Broadcast" - Data packet that will be sent to all nodes on a network. Broadcasts are identified by a "broadcast address" a 'host address' of all ones in the 'IP address'.

The Cisco IOS software supports two kinds of broadcasts:

  1. "Directed broadcasts" - Broadcasts directed into a specific network are allowed and are forwarded by the router. These directed broadcasts contain all ones in the host portion of the address.
  2. "Flooding" - 'Flooding broadcasts' (255.255.255.255) are not propagated, but are considered local broadcasts.

"Flooding" - Traffic passing technique used by 'switches' and 'bridges' in which traffic received on an interface is sent out to all of the interfaces of that device except the interface on which the information was originally received.

"Network Addresses" - An address of all zeros means 'this network' or 'the wire itself'. The "routing table" contains entries for the 'wire' or 'network addresses'; it usually does not contain any information about hosts.

An 'IP address' and 'subnet mask' on an interface achieves three purposes:

  1. It enables the system to process the receipt and transmission of packets.
  2. It specifies the device's local address.
  3. It specifies a range of addresses that share the cable with the device.

1. If a router has:

A serial interface SO with IP address 172.16.1.2
An Ethernet interface EO with IP address 172.31.4.1
A Token Ring interface TO with IP address 172.31.16.1
and if all interfaces use a mask of 255.255.25.0, find the subnet (wire) number for each interface. 

SO: 172.16.1.0		(172.16.1.2	AND	255.255.255.0)
EO: 172.31.4.0		(172.31.4.1	AND	255.255.255.0)
TO: 172.31.16.0		(172.31.16.1	AND 	255.255.255.0)

2. What is the result of the command:

"Router(config-if)#   ip address   ip-address subnet-mask"

This command establishes the 'logical network address' (ip-address) and subnet-mask of the specified interface. Specifically, it (1) assigns an address and a subnet-mask and (2) starts IP processing on that interface.

"Router(config)# term ip netmask-format"
Command used to specify the format of network masks for the current session. Format options are:
Bit count
Dotted decimal (the default)
Hexdecimal
What does the following command do?
    "Router(config)#   ip host name ip-address"
The 'ip host' command makes a "static name-to-address entry" in the router's configuration file. Hosts and interfaces then become selctable by either their 'name' or their 'IP address'.

    "Router(config)#   ip name-server server-address [...]"
Command used to define which hosts can provide the 'name service'. A maximum of six IP addresses can be specified as name servers in a single command.

    "Router(config)#   ip domain-lookup"
The DNS (name service) is enabled by default with a server address of 255.255.255.255, which is a local broadcast.

    "Router(config)#   no ip domain-lookup"
Command used to turn off name-to-address translation in the router.
4. What type of information is obtained from the command:
"Router# show hosts"
This command displays host names, their associated IP addresses, and type and time status indicators about how and why the host name became associated with those IP addresses (Cache of host name-to-address mappings).

The Cisco IOS software maintains a 'cache' of 'host name-to-address mappings' for use by EXEC commands. This cache speeds the process of converting names to addresses.

5. Distinguish amongst the three commands which allow you to 'verify address configuration' in your internetwork.

  1. "Telnet" (a layer 7 test) verifies the allplication layer software between source and destination stations (this is the most complete test mechanism available).

  2. "Ping" (a layer 3 test) uses the IMCP protocol to verify the hardware connection and the logical address of the network layer (this is a very basic testing mechanism). The 'ping' command sends ICMP echo packets and is supported in both user and privileged EXEC mode. These are the commands that may be returned by the "ping" test (ICMP Echo Request): 
    
Character    Definition
   !	     Successful receipt of an echo reply
   .	     Times out waiting for datagram reply
   U	     Destination unreachable error
   C	     Congestion-experienced packet
   I	     Ping interupted (Ctrl-Shift-6 x)
   ?	     Packet type unknown
   &	     Packet Time To Live exceeded
    "Extended Ping" is supported only from privileged EXEC mode. You can use the extended command mode of the ping command to specify the supported internet header options. To enter the extended mode, enter 'Y' at the extended commands prompt.

  3. "Trace" uses Time-To-Live (TTL) values to generate messages from each router used along the path (this is very useful for locating path failures). 'Host names' are shown if the addresses are translated dynamically or via static host table entires. The 'times' listed represent the time required for each of three probes to return.

When the trace reaches the target destination, an asterisk (*) is reported at the display. This normally is caused by the receipt of a port -unreachable packet and the time out in responce to the probe packet. Other responses include: 


!H    -		The probe was received by the router,
		but not forwarded, usually due to an 
		access list.
 P    -		The protcol was unreachable.
 N    -		The network was unreachable.
 U    -		The port was unreachable.
 *    -		Time out.
[Previos]Lesson 11         [Index]Index         [Next]Next
[Top of Page]     This page is maintained by:   Michael P. Harris
[Viking Home Page] viking.delmar.edu
Last updated April 2		 [E-mail] mpharris@surf.delmar.edu
Copyright © 1999