Sunday 17 February 2013

Internet Layer Protocols

Posted by Puneet Sharma on 00:33 Networking No comments

The Protocols at the Internet Layer are:

Internet Protocol (IP):

IP is used for unique identification of a device within a network.
IP receives segments from the Host-to-Host layer and fragments them into datagrams (packets) if necessary. IP then reassembles datagrams back into segments on the receiving side.
IP is of two types: IPv4(32 Bit Address) and IPv6(128 Bit Address)
Port no.= For IPv4 is 0 and For IPv6 is 41
Protocol used= UDP(User Datagram Protocol) for both IPv4 and IPv6.

Internet Control Message Protocol (ICMP):

It works at the network layer and is used by IP for many different services.
ICMP is a management protocol ans messaging service provider for many different services.
ICMP messages are carried as IP datagrams.
Characteristics of ICMP packets are: They can provide hosts with information about network problems.They are encapsulated within IP datagrams.
Ping(Packet Internet Groper) uses ICMP echo request and reply messages to check connectivity of machines on an inter-network.
Traceroute using ICMP time-outs, Traceroute is used to discover the path a packet takes as it traverses an inter-network.
Port no.= 1 for IPv4 and 58 for IPv6

Address Resolution Protocol (ARP):

Address Resolution Protocol (ARP) finds the hardware address(mac address) of a host from a known IP address i.e ARP Reverse Address Resolution Protocol (RARP) IP address to Ethernet(MAC) addresses.
Working: When IP has a datagram to send, it must inform a Network Access protocol, Such as Ethernet or wireless, of the destination's hardware address on the local network. If IP doesn't find the destination host's hardware address in the ARP cache, it uses ARP to find this information. ARP interrogates the local network by sending a broadcast asking the machine with the specified IP address to reply with its hardware address.
ARP resolves 32 bit(IPv4) or 128 bit(IPv6) addresses into 48 bit(MAC) addresses.

Reverse Address Resolution Protocol (RARP):

Reverse Address Resolution Protocol (RARP) finds the IP address of a host form a known MAC address i.e Reverse Address Resolution Protocol (RARP) resolves Ethernet(MAC) addresses to IP addresses.
Working: RARP discovers the identity of the IP address for diskless machines by sending out a packet that includes its MAC address and a request for the IP address assigned to the MAC address.

Proxy Address Resolution Protocol (Proxy ARP):

Proxy ARP can actually help machines on a subnet reach remote subnets without configuring routing or even a default gateway.
Advantage of using Proxy ARP is that it can be added to a single router on a network without disturbing the routing tables of all the routers that live there too. But Proxy ARP will definitely increase the amount of traffic on your network segment.
Proxy ARP is configured on all CISCO routers by default.
Proxy ARP is not really a separate Protocol. It is a service run by routers.

Gratuitous ARP:

Gratuitous ARP mean both Gratuitous ARP request or Gratuitous ARP reply.
A Gratuitous ARP request is an ARP request packet where the source and destination IP are both set to the IP of the machine issuing the packet and the destination MAC is the Broadcast address ff:ff:ff:ff:ff:ff .Ordinarily, no reply packet will occur.
A Gratuitous ARP reply is a reply to which no request has been made.
They can help to detect IP conflicts.

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