IP

IP (Internet Protocol) is an identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 10.5.25.180.

Every computer that communicates over the Internet is assigned an IP address that uniquely identifies the device and distinguishes it from other computers on the Internet. Within an isolated network, IP addresses can be assigned at random if each one is unique. However, to connect a private network to the Internet, registered IP addresses must be used (called Internet addresses) to avoid duplicates. The four numbers in an IP address are used in different ways to identify a particular network and a host on that network.

Four regional Internet registries—ARIN, RIPE NCC, LACNIC, and APNIC—assign Internet addresses from the following three classes.

Class A - supports 16 million hosts on each of 126 networks
Class B - supports 65,000 hosts on each of 16,000 networks
Class C - supports 254 hosts on each of 2 million networks

The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR (Classless Inter-Domain Routing) is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6. ICMP (Internet Control Message Protocol) is an extension to the IP defined by RFC 792. ICMP supports packets containing error, control, and informational messages. For example, the ping command uses ICMP to test an Internet connection.

The IP implements all components required for IP forwarding. The various components of the IP include ARP, RARP, RTM, ICMP, IRDP, IGMP, InARP, BOOTP, TFTP, TRACE ROUTE, PING and UDP.

arp
To add a static entry in the ARP cache or set the ARP (Address Resolution Protocol) cache timeout, use the command arp in Global Configuration Mode. The no form of this command resets ARP cache timeout to its default value or deletes a static entry from the ARP cache.
clear ip arp
To clear dynamically learnt ARP entries, use the command clear ip arp in Global Configuration Mode.
ip aggregate-route
To set the maximum number of aggregate routes, use the command ip aggregate-route in Global Configuration Mode. The no form of this command sets the maximum number of aggregate routes to its default value. Aggregate Route-based IP switching is achieved by creating a virtual circuit along the network by selecting the forwarding paths used by routers that use OSPF (Open Shortest Path First Protocol). The data is sent through these virtual circuit to the destination. The routing process is skipped along this circuit. The data is tagged with a label that is read by the switches and forwarded to the destination.
ip arp max-retries
To define the maximum number of ARP requests that the switch generates before deleting an unresolved ARP entry, use the command ip arp max-retries in Global Configuration Mode. The no form of this command sets the maximum number of ARP request retries to their default value.
ip default-distance
To configure the default administrative distance for static IPv4 routes, use the command ip default-distance in Global Configuration Mode.
ip default-ttl
To set the Time-To-Live ( TTL) value, use the command ip default-ttl in Global Configuration Mode. The no form of this command sets the TTL to the default value.
ip directed-broadcast
To enable forwarding of directed broadcasts, use the command ip directed-broadcast in Interface Configuration Mode. The no form of this command disables the forwarding of directed broadcasts. The IP directed broadcast is an IP packet whose destination is a valid IP subnet address, but with a source from a node outside the destination subnet. The routers from outside the subnet forward the IP directed broadcast like any other IP packet. When the directed packet reaches a router in the destination subnet, the packet is exploded as a broadcast in the subnet. The header information on the broadcast packet is rewritten for the broadcast address in the subnet. The packet is sent as link-layer broadcast.
ip echo-reply
To enable sending ICMP Echo Reply messages, use the command ip echo-reply in Global Configuration Mode. The no form of this command disables sending ICMP Echo Reply messages. The “ip echo reply” is a message sent by a device in response to a request sent by another device. This message is used to check if a device is able to communicate (send and receive data) with the destination device.
ip mask-reply
To enable sending ICMP Mask Reply messages, use the command ip mask-reply in Global Configuration Mode. The no form of this command disables sending v Mask Reply messages. The IP mask reply is an ICMP message sent with the subnet mask of the network by the router to the host. This reply is in correspondence to a request sent by the host seeking the subnet mask of the network.
ip path
To initiate path MTU (Maximum Transmission Unit) discovery and configure the MTU for usage in path PMTU (PMTU) discovery, use the command ip path in Global Configuration Mode. The no form of this command sets MTU for usage in PMTU Discovery and resets PMTU discovery to its default value.
ip proxy-arp
To enable proxy ARP for the interface, use the command ip proxy-arp in Interface Configuration Mode. The no form of this command disables proxy ARP for the interface.
ip proxyarp-subnetoption
To enable proxy ARP subnet check, use the command ip proxyarp-subnetoption in Global Configuration Mode. When subnet check is enabled, iSS acts as ARP proxy for target address in different subnet. The no form of this command disables proxy ARP subnet check. iSS acts as ARP proxy for target address in same or different subnet that is used in IP-DSLAM (Digital Subscriber Line Access Multiplexer) case, when subnet check is disabled.
ip rarp client
To enable RARP (Reverse Address Resolution Protocol) client, use the command ip rarp client in Global Configuration Mode. The no form of this command disables the RARP client. The RARP resolves an IP address from a given hardware address. The client that requests for the IP is the RARP client. The IP address of the default interface is obtained through RARP, when the IP address configuration mode is dynamic. After finishing the RARP Max retries, IP is obtained through DHCP (Dynamic Host Configuration Protocol).
ip redirects
To enable sending Internet Control Message Protocol ( ICMP Redirect) messages, use the command ip redirects in Global Configuration Mode. The no form of this command disables sending ICMP Redirect messages. The Redirect Message is an ICMP message which notifies a host to update its routing information to send packets on an alternate route when a packet enters an IP interface and exits the same interface. The redirect message is sent to inform the host of the presence of alternative route.
ip unreachables
To enable the router to send an ICMP unreachable message to the source if the router receives a packet that has an unrecognized protocol or no route to the destination address, use the command ip unreachables in Global Configuration Mode. The no form of this command disables sending ICMP unreachable messages. ICMP provides a mechanism that enables a router or destination host to report an error in data traffic processing to the original source of the packet. This informs the source that the packet is dropped.
ipv4 enable
To enable IPv4 processing on the interface that has not been configured with an explicit IPv4 address, use the command ipv4 enable in Interface VLAN Configuration Mode. When subnet check is enabled, the switch acts as an ARP proxy for target address in different subnet. The no form of this command disables IPv4 processing on the interface.
maximum-paths
To set the maximum number of paths that can be connected to a host, use the command maximum-paths in Global Configuration Mode. The no form of this command sets the maximum number of paths to its default value. The command provides multiple forwarding paths for data traffic and enables load balancing. It improves the overall network fault tolerance, as a failure in one instance does not affect the other instances.
ping
To send echo messages, use the command ping in Privileged EXEC Mode. The Packet Internet Groper ( PING) module is built based on the ICMP echo request and ICMP echo response messages. The network administrator uses ping on a remote device to verify its presence. PING involves sending ICMP echo messages repeatedly and measuring the time between transmission and reception of message. The output displays the time taken for each packet to be transmitted, number of packets transmitted, number of packets received, and packet loss percentage.
show ip default-distance
To display the default administrative distance for static IPv4 routes, use the command show ip default-distance in Privileged EXEC Mode.
show ip proxy-arp
To display the status of the proxy ARP for all created interfaces, use the command show ip proxy-arp in Privileged EXEC Mode.
traffic-share
To enable enables traffic sharing (load sharing of IP packets), use the command traffic-share in Global Configuration Mode. The no form of this command disables traffic sharing. Traffic sharing is the process by which the protocols select the route for traffic flow with regard to path cost calculation and load distribution. EIGRP (Enhanced Interior Gateway Routing Protocol) provides intelligent traffic sharing. Traffic sharing is controlled by selecting the mode of distribution. Traffic-share balanced distributes the traffic proportionately to the ratio of the metrics of different routes. The traffic-share min distributes the traffic in the route which has minimal cost path even if different paths are available.
debug ip arp
To set the debug level for ARP module and generate debug statements for the specified trace level or for all traces, use the command debug ip arp in Privileged EXEC Mode. The no form of the command disables the tracing in ARP module.
ip route
To add a static route, use the ip route command in Global Configuration Mode. The route defines the IP address or interface through which the destination can be reached. The no form of this command deletes a static route. If the static route is configured without any metric value, the route will be configured with metric value 1.
ip routing
To enable IP routing, use the command ip routing in Global Configuration Mode. The no form of this command disables IP routing. IP routing is the path defined by set of protocols for the data to follow across multiple networks from source to its destination. When an IP packet is to be forwarded, the router uses its forwarding table to determine the next hop address. The header in the IP packet has the next hop information.
show ip arp
To display the IP ARP table, use the show ip arp command in Privileged EXEC Mode.
show ip information
To display IP configuration information, use the command show ip information in Privileged EXEC Mode.
show ip pmtu
To display the configured PMTU entries, use the command show ip pmtu in Privileged EXEC Mode. The details include Destination IP address, Type of Service ( ToS), and PMTU.
show ip rarp
To display RARP configurations’ information such as maximum number of RARP request retransmission retries and RARP request retransmission timeout, use the command show ip rarp in Privileged EXEC Mode. The number of responses discarded are also displayed.
show ip route
To display the IP routing table, use the show ip route command in Privileged EXEC Mode.
show ip traffic
To display the IP protocol statistics, use the show ip traffic command in Privileged EXEC Mode.
traceroute
To trace a route to the destination IP, use the traceroute command in Privileged EXEC Mode.