What is Routing:-
1.routing is the process of taking packet from one network to another.
2.this is done by routing protocol.
3.to work with routing protocol a router must need minimum information to select the best path.:destination address, source address,possible route to destination and shortest and best path to reach the destination.
4.Before to understand the working of routing protocol it is very important to understand how packet move from one network to another.
Host A want to send packet to Host B.:-
1.icmp protocol will make the echo request.(data payload).
2.icmp handover this echo to ip
3.ip then build up the packet.
4.At minimum ip contain source ip ,destination ip and protocol.
5.ip will check the destination address .
6.since destination is not local packet will go to default gateway.(router A)
7.mac address of router A should be resolved.this process is done by arp protocol.
8.once mac and ip resolved packet will send for framing.mac is used to provide access to media and frame will send to each device for error detection.once the frame process is complete packet is pulled from frame. and frame is discarded.
9.router will check the routing table for destination address.if found then process to next interface. if not found
message is sent by icmp that destination is not reachable.
10.now at exit interface packet again encapsulate with WAN technology like PPP frame. from router A source layer 2 will be router A exit interface. destination layer 2 will be router B incoming interface.where as layer 3 s and destination will remain the same.that is source layer 3 host A and destination layer 3 is host B.
11.now packet reach at router B. same process will occur here LAN technology is used with Ethernet frame.
12.now host b mac and ip should be resolved. if not arp process again resolve the addresses.
13.finally packet will reach at host B.
14.icmp will send the echo reply ack. if there is any problem then message will go request time out.this shows that packet while returning with ack having problem. check destination router. for solve the problem.
Focus on these points:-
Routing Process from Host A to Host B
Remember frame address(layer 2) change at each Link of router where as packet address( layer 3)remain the same.
1.routing is the process of taking packet from one network to another.
2.this is done by routing protocol.
3.to work with routing protocol a router must need minimum information to select the best path.:destination address, source address,possible route to destination and shortest and best path to reach the destination.
4.Before to understand the working of routing protocol it is very important to understand how packet move from one network to another.
Host A want to send packet to Host B.:-
1.icmp protocol will make the echo request.(data payload).
2.icmp handover this echo to ip
3.ip then build up the packet.
4.At minimum ip contain source ip ,destination ip and protocol.
5.ip will check the destination address .
6.since destination is not local packet will go to default gateway.(router A)
7.mac address of router A should be resolved.this process is done by arp protocol.
8.once mac and ip resolved packet will send for framing.mac is used to provide access to media and frame will send to each device for error detection.once the frame process is complete packet is pulled from frame. and frame is discarded.
9.router will check the routing table for destination address.if found then process to next interface. if not found
message is sent by icmp that destination is not reachable.
10.now at exit interface packet again encapsulate with WAN technology like PPP frame. from router A source layer 2 will be router A exit interface. destination layer 2 will be router B incoming interface.where as layer 3 s and destination will remain the same.that is source layer 3 host A and destination layer 3 is host B.
11.now packet reach at router B. same process will occur here LAN technology is used with Ethernet frame.
12.now host b mac and ip should be resolved. if not arp process again resolve the addresses.
13.finally packet will reach at host B.
14.icmp will send the echo reply ack. if there is any problem then message will go request time out.this shows that packet while returning with ack having problem. check destination router. for solve the problem.
Focus on these points:-
Routing Process from Host A to Host B
(1) Host A to Switch A to Router A :
· L2 Source Addr = MAC Host A
· L2 Dest Addr
· L3 Source Addr = IP Host A
· L3 Dest Addr
(2) Router A to Router B :
· L2 Source Addr = MAC Router A
· L2 Dest Addr
· L3 Source Addr = IP Host A
· L3 Dest Addr
(3) Router B to Switch B to Host B :
· L2 Source Addr = MAC Router B
· L2 Dest Addr
· L3 Source Addr = IP Host A
· L3 Dest Addr
Remember frame address(layer 2) change at each Link of router where as packet address( layer 3)remain the same.
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