What are classless routing protocols

More commonly referred to as classless routing behaviour in reference to protocols. examples are ripv2, eigrp, ospf, isis etc. classless routing protocols submit subnet information in the data they send to other routers. therefore, variable subnet masks can be applied other than the default classful subnet mask. i.e, if the first two bits in the first octet are 0 then it is a class A address, and the first octet only, /8 or 255.0.0.0, is the network portion. hence why the private routing address 10.0.0.0 extends all the way to 10.255.255.255. with classless routing behaviour this can be any subnet mask.

Understanding Routing Protocols

The IP protocol is the most common of the routed protocols. AppleTalk and Novell IPX still exist in some networks but are no longer as common as they were a few years ago. How does a routed protocol behave? Let’s examine an IP packet in our fictitious Sprockets corporate network.
In this example, an Intel PC controlling robot, on the manufacturing floor segment of the Sprockets’ network, will make a database query to an IBM mainframe host, on the data center network segment. The manufacturing segment media is fast Ethernet and the IBM host segment is on token ring. A layer 3 IP datagram will have traverse different layer 2 encapsulations and layer 1 media.

Both the IBM mainframe and the manufacturing floor robot controller are configured to use the layer 3 IP routed protocol. The IP datagram, originating in the controller PC, assigns the destination address of 123.21.3.47, the IP address of the IBM mainframe. The IP datagram is encapsulated in a layer 2 Ethernet frame and placed onto the wire. The beauty of the IP protocol is that a datagram doesn’t know how to directly get to its destination. This is the work of a routing protocol.

Exterior routing protocols

Exterior Gateway Protocols (EGPs) route between separate autonomous systems. Examples include:
1.EGP (the original Exterior Gateway Protocol used to connect to the former Internet backbone network; now obsolete)
2.BGP (Border Gateway Protocol: the current version, BGPv4, dates from around 1995)
3.CSPF (Constrained Shortest Path First)

Interior routing protocols

1.IGRP (Interior Gateway Routing Protocol)
2.EIGRP (Enhanced Interior Gateway Routing Protocol)
3.OSPF (Open Shortest Path First)
4.RIP (Routing Information Protocol)
5.IS-IS (Intermediate System to Intermediate System)

shiyaaan [IGRP] Note that IGRP, a Cisco proprietary routing protocol, is no longer supported. EIGRP accepts IGRP configuration commands, but the internals of IGRP and EIGRP are completely different.

What is the use of proxy ARP?

When routers receive ARP requests from one network for hosts on the network, they will respond with a ARP reply packet with their MAC address. For example, let us say host A is in one network, host B is in another network and router C connects these two networks. When host A sends an ARP request to resolve the IP address of host B, the router C receives this packet. The router C sends an ARP reply with its MAC address. So host A will send all the packets destined for host B to the router C. Router C will then forward those packets to host B. Proxy ARP is also used if a host in a network is not able to understand subnet addressing. For example, if host A and host B are actually in two different subnets, but host A cannot understand subnet addressing. So host A assumes that host B is present in the same network. In this case a router, host C, can use proxy ARP to route packets between host A and host B.

What is proxy ARP?

Proxy ARP is the process in which one system responds to the ARP request for another system. For example, host A sends an ARP request to resolve the IP address of host B. Instead of Host B, Host C responds to this ARP request.

What happens when a host receives an ARP request packet?

The ARP request is received and processed by all the hosts in the network, since it is a broadcast packet.
The following steps are carried out when a ARP request packet is received by a host:
1.If the IP address to be resolved is for this host, then the ARP module sends an ARP reply packet with its Ethernet MAC address.
2.If the IP address to be resolved is for this host, then the ARP module updates its ARP cache with the source Ethernet MAC address to source IP address mapping present in the ARP request packet. If the entry is already present in the cache, it is overwritten. If it is not present, it is added.
3.If the IP address to be resolved is not for this host, then the ARP module discards the ARP request packet.

When is an ARP request packet generated?

The following steps results in the generation of an ARP request packet:
1.The IP module sends a packet, destined for another host in the network, to the ARP module.
2.The ARP module looks up the ARP table (cache) to resolve the IP address.
3.If the supplied IP address is present in the ARP cache, it is resolved into its Ethernet address.
4.If the ARP module is not able to find an entry for this IP address in the ARP cache, then it sends an ARP
request packet to the Ethernet driver, to resolve the IP address to the Ethernet address.
5.After the IP address is resolved by the ARP module, the packet is sent to the Ethernet driver for transmission.

What is an ARP cache?

ARP maintains the mapping between IP address and MAC address in a table in memory called ARP cache. The entries in this table are dynamically added and removed

What is the use of ARP?

A host in an Ethernet network can communicate with another host, only if it knows the Ethernet address (MAC address) of that host. The higher level protocols like IP use a different kind of addressing scheme (like IP address) from the lower level hardware addressing scheme like MAC address. ARP is used to get the Ethernet address of a host from its IP address. ARP is extensively used by all the hosts in an Ethernet network.

What is ARP?

Address Resolution Protocol (ARP) is a network protocol, which maps a network layer