Configuring IP Addressing Directory

List of Task for IP Addressing

Configuring IP Address at the Network Interface

Configuring Address Resolution

Configuring a router progress

Configuring Broadcast Packet Processing

Detecting and maintaining IP Addressing

Demonstration of IP Addressing 

 

 

List of Task for IP Addressing

The basic and necessary requirement for configuring IP is to configure IP address at the network interface of router. Only by doing so, the interface can be activated and can communicate with other systems through IP. At the same time, IP network mask shall be determined simultaneously.

In order to configure IP addressing, the following tasks shall be accomplished, of which the first task is necessary, the rest are optional.

Configuring IP Address at the Network Interface

Configuring Address Resolution

Configuring a router progress

Configuring Broadcast Packet Processing

Detecting and maintaining IP Addressing

The last part “Demonstration of IP Addressing” tells how to set up IP address on the network

Configuring IP Address at the Network Interface

   IP address determines that IP packet can be transmitted to destination address. Some IP addresses are reserved for their special purpose and  cannot be used as the address of host computer or network address. Form 1 lists the scope of IP address, the reserved address and usable IP address.

Form 1

Category

Address or Scope

Status

A

0.0.0.0

1.0.0.0 to 126.0.0.0

127.0.0.0

Reserved

Usable

Reserved

B

128.0.0.0 to 191.254.0.0

191.255.0.0

Usable

 Reserved

C

192.0.0.0

192.0.1.0 to 223.255.254

223.255.255.0

Reserved

 Usable

Reserved

D

224.0.0.0 to 239.255.255.255

Multi-list Broadcasting Address

E

240.0.0.0 to 255.255.255.254

255.255.255.255

 Reserved

Broadcast 

 

The description of IP address can be referred to RFC 1166 Internet numbers”. If the usable network address is needed, you can contact Internet service provider.

One interface can have only one IP primary address. The following command is used for configuring primary IP address of network interface and network mask under interface configuration model. 

Command

 Purpose

ip address ip-address mask

Configuring the primary IP address of interface

Mask means the sector of network in IP address


Note: We only support the network mask arranged in the order of consecutive setting from the top of network bit sequence .


Other additional and optional IP addressing will be introduced in the later part.

Configuring Multiple IP Addresses at Network Interface

Activating IP Processing Function at Serial Port

 

Configuring Multiple IP Addresses at Network Interface

Each interface can have multiple IP address, including a primary IP address and unlimited number of secondary IP address. Under the following cases, the secondary IP address needs to be configured:

When a specific network band does not have enough IP address, for example, some logic sub-network has only 254 valid IP addresses. But in real physical network, three hundred host computers need to be linked. By configuring secondary IP address at router or access server, a physical sub-network can be shared by two logic sub-networks.

Many early networks were based on the second layer bridge rather than divided into a lot of sub-networks. The right utilization of secondary IP address can transformed the early networks into multiple sub-networks based on router. Through configuring secondary IP address, the router on the network can understand the multiple  sub-networks in the physical network.

When two sub-networks of a network are divided by another network physically, the address of the network can be used as secondary IP address, thus the two physically divided networks in a logic network can be linked together logically.


Note: If either of routers at a network band is configured with a secondary address, the other routers at the same network band need to be configured with secondary IP address with same network band.


The following command is used for configuring multiple IP addresses under interface configuration model.

Command

Purpose

ip address ip-address mask secondary

Configuring multiple IP address at the network interface 


Note: When IP router protocol transmits the updated information, it may treat the secondary IP address in a different way.


 

Activating IP Processing Function at Serial Port

You may hope that serial port or a tunnel interface has IP Processing function without configuring IP address. When such interface produces a packet, for instance, when a router updates packet, the source address used by the interface is the valid IP address of other interface of your designated router. Such kind of interface is called unnumbered interface. The router still uses IP address whose interface is designated to determine the router that transmits the updated packet at the unnumbered interface. The following are rules:

By encapsulating the serial port of HDLCSLIPPPPLAPB and FR and tunnel interface, IP packet can be processed even without configuring IP address. For the encapsulated FR serial port, it shall be a point to point sub-interface. The IP processing function is not usable to the encapsulated X.25 and SMDS interface

Such kind of interface cannot be determined whether it works normally as it has no IP address. But its status can be detected remotely by using SNMP.


Note: It shall be very careful when this configuration is used on the serial link between the different main networks. The router protocol running on the link should be configured that does not broadcast any information of sub-networks .


Under the interface configuration model, the following command is used for activating IP processing function at unnumbered serial port:

Command

Purpose

ip unnumbered type number

Activating IP processing function without configuring IP address at serial interface or tunnel interface.

The interface designated by the said command shall be another interface of the router with IP address and shall not be an unnumbered interface. This interface shall be activated (indicated by “up” in the command “show interfaces).

The last part of this Chapter “Demonstration of Serial Configuration” shows how to configure serial port.

 

Configuring Address Resolution

IP implementation allows the control of IP address resolution and some other functions. The following is the introduction of how to configure address resolution.

Setting up Address Resolution

Mapping host name to IP Address 

 

Setting up Address Resolution

One IP equipment has two addresses: one is local address (the one that identify the equipment in local network band or LAN) the other is network address (it indicates the network band the equipment belong)  The local address is the link layer address as it contains at the head section of frame of link layer and is read and used by the equipment of link layer. The professionals call it MAC address because the sub-layer of Media Access Control in the link layer is used to process address.

For example, The communication with an equipment on Ethernet needs to know its 48 byte MAC or local data link layer address. The process of obtaining local data link layer address from IP address is called address resolution protocol (ARP). The process of obtaining IP address from local date link layer address is called reverse address resolution.

The system uses two kinds of address resolution: Address Resolution Protocol and Proxy ARP. The ARP and proxy ARP are defined in RFC 826 and 1027 respectively.

ARP is used to map IP address to media or MAC address. If IP address is known, ARP determines the corresponding MAC address. Once MAC address is determined, the relationship of IP address /MAC address will be saved at ARP cache so as to be obtained quickly. Then IP packet can be encapsulated in the frame of link layer and transmitted to the network.

The configuration of IP address resolution includes the following tasks:

Defining a static ARP Cache entity

Activating Proxy ARP

Defining a static ARP Cache entity

ARP and other address resolution protocol provide the dynamic mapping between IP address and media address. As most of host computers support dynamic address resolution, the static ARP cache entity does not need to be configured. If it is necessary to define static ARP cache entity, it can be defined under global configuration model by setting up a permanent list item in ARP cache. The system will use the list item to translate 32 byte IP address into 48 byte hardware address. In addition, a router can be designated to respond the ARP request.

The maximum entry of static ARP can be 2000. Because static ARP and dynamic ARP use the same cache, the sum of static ARP and dynamic ARP can not exceed 2000 entries。

If ARP is not preferred to exist permanently, the existing time of ARP list item can be set. The following two forms list how to configure the static IP address/media address mapping

Under global configuration model, one of the following commands is used for address mapping:

Command

Purpose

arp ip-address hardware-address

In ARP cache, global address maps an IP address to media address

arp ip-address hardware-address alias

Designating a router to respond to ARP request of IP address with its own media address.

The following commands are used under interface configuration model.

Command

Purpose

arp timeout seconds

Setting the timeout for ARP cache item in ARP cache

The command “show interfaces” are used to show ARP timeout of specific interface. The command “show arp” is used to check ARP content in cache. The command “clear arp-cache” is used to clear all list items in ARP cache. 

Activating Proxy ARP

The system uses proxy ARP (RFC 1027 definition) to help the host computer without the corresponding router obtain the media address located at other network. For example, When router receives an ARP request, it will make a proxy ARP response telling its local link layer address if router finds that its requested host computer and the host computer making the request are not linked to the same interface of router, and the router is linked to all the routers of host computer through other interface rather than the interface that receives ARP request. The host computer will transmit the packet to router, the router will retransmit the packet to destination host computer. Proxy ARP function default is activated.

Under interface configuration model, the following commands are used to activate ARP:

 

Command

Purpose

ip proxy-arp

Activating proxy ARP at the interface

 

Mapping host name to IP Address

An IP address can have a name of host computer to match. The system saved a host computer name that can be used by the command “telnetping” in the mapping cache.

Under global configuration model, the following command is used for designating the mapping from host computer’s name to address.

Command   

Purpose

ip host name address

Static mapping host computer’s name to IP address

Configuring a router progress

  Based on the said configurations, the user can configure one or multiple router protocols on the needs of respective network. Router protocol provides the information of topology related to Internet. IP router protocol configuration, such as BGPRIPOSPF, will be described in the later part of the document.

Configuring Broadcast Packet Processing

The destination address of broadcast packet is the whole host computers in a physical network. The network host identifies the broadcast packet through special address. Some protocols frequently uses broadcast packet, including some important Internet protocol. Controlling broadcast packet is a basic work of IP network administrator . The system supports special direct broadcast and does not support the broadcast of whole sub-networks in a network.

Some early IP implementation did not use the standard of current broadcast address. They used “0” rather than “1” to stand for broadcast address. Therefore, the system can identify and receive these two kinds of packet.

Allowing the translation from directional broadcasting to Physical broadcasting

Re-transmitting UDP Broadcasting Packet

Allowing the translation from directional broadcasting to Physical broadcasting

Under default status, IP direct broadcast packet will be discarded rather than retransmitted. The discarded of IP direct broadcast packet enables router to be free of such kind of attack of “deny of service”.

User can activate the retransmission function of IP direct broadcast at the interface where the direct broadcast is translated into physical broadcasting. If this retransmission is activated, all the direct broadcast packet of the network where the interface lie will be retransmitted to the interface, then the direct broadcast packet will be retransmitted as physical broadcasting frame.

User can designate an access list to control the retransmission of the broadcasting packet. When access list is designated, IP packet that is accepted by access list can be translated from direct broadcast to physical broadcast.

Under interface configuration model, the following command is used for activating the retransmission of IP direct broadcast.

Command

 Purpose

ipdirected-broadcast  [access-list-name]

Allowing the translation from direct broadcast to physical broadcast at an interface.

Re-transmitting UDP Broadcasting Packet

Sometimes, network host uses UDP broadcasting packet to determine the information of address, configuration, name and other information. If the network where the host is located has no corresponding server and these UDP packet can not be re-transmitted under general condition, the host will not obtain these information. In order to solve this issue, user can configure some type of broadcast packet at the corresponding interface to retransmit the broadcasting packet to a help address. An interface can be configured with multiple help addresses.

User can designate a UDP destination port to prevent these UDP packets from being retransmitted. Currently, the packet retransmitted by the system default to destination port is UDP packet of NetBIOS name service (port 137)

If the retransmission is allowed and destination address is designated, the following command is used under interface configuration model.

Command

 Purpose

ip helper-address address

Allowing the retransmission of UDP broadcasting packet and designating destination address.

Under global configuration model, the following command is used for designating the retransmission of the protocols.

Command

Purpose

ip forward-protocol udp [port]

Designating the UDPprotocol of the interfaces to be retransmitted.

Detecting and maintaining IP Addressing

In order to detect and maintain network, the following operation shall be carried out:

Clearing cache, Lists and Database

Showing System and Network Statistics 

 

Clearing cache, Lists and Database

User can clear a cache, lists and all the contents in the database. When some cache, list or the contents in the database is invalid, it shall be cleared.

The following command is used for the operation in the following form that is related to clearing cache, list and database.

Command

Purpose

clear arp-cache

Clearing IP ARP cache

Showing System and Network Statistics

The system can show the specific statistic, such as IP routing table, cache and database. This information can help to determine the utilization of system resources so as to settle the network issue. The system can show accessibility to the end-point and the course of the transmitted packet in the network.

These operations are listed in the following table. The specific method of using these commands can be referred to the chapter “The Command of IP Addressing”. The following command is used under management model.

Command

Purpose

show arp

Showing the content in ARP table

show hosts

Showing host name-IP address mapping cache table

show ip interface [type number]

Showing the status of interface

show ip route [protocol]

Showing the current status of router

ping {host | address}

Detecting the accessibility to network end-point

Demonstration of IP Addressing

The following is the example of IP configuration

 

Demonstration of Serial Port Configuration

Serial port (serial 1/0) uses the address of ethernet1/1 in the following example.

 

interface ethernet 1/1

  ip address 202.96.2.3 255.255.255.0

interface Serial 1/0

  ip unnumbered ethernet 1/1