November | 2012 | The Quasar Syncopation

So , I’ve always wondered what exactly is IP Routing all about? I mean what exactly does each layer do? So I sneaked around , saw the bits move , saw the payload put inside a container with some buddy bits , who were in turn put inside another container with some other buddies upto 4 layers.

This is the INCEPTION of Networking.

Yo Dawg , I heard you like INCEPTION.

Anway , so this is how it’s done.

Topology

Configurations

PC0

Static IP Set : 172.16.10.2 | 255.255.255.0 . Default Gateway : 172.16.10.1

PC1

Static IP Set : 172.16.20.2 | 255.255.255.0 . Default Gateway : 172.16.20.1

Router Config

Router>en

Router#config t

Enter configuration commands, one per line. End with CNTL/Z.

Router(config)#int fa0/0

Router(config-if)#ip address 172.16.10.1 255.255.255.0

Router(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet0/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up

Router(config-if)#exit

Router(config)#int fa1/0

Router(config-if)#ip address 172.16.20.1 255.255.255.0

Router(config-if)#no shutdown

%LINK-5-CHANGED: Interface FastEthernet1/0, changed state to up

%LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0, changed state to up

—————————————————————–

ICMP creates an echo request payload which is alphabet in data field.
ICMP hands the payload to IP(Internet Protocol) , which creates a Packet.
After the packet is created , IP determines whether the destination is local or remote.
If the network is external (remote) , the Widows Registry is parsed to find the configured default gateway.
PC0 (172.16.10.2) is configured on 172.16.10.0 network. PC1(172.16.20.2) is configured on 172.16.20.0 network.
- if(Packet = free)
- { hand packet to the Data Link Layer for framing : ARP has worked}
- if(Packet != free)
  { ARP Broadcast is sent to all local machines to search for hardware address of 172.16.10.1}
- if(Packet != free)
- { ARP Broadcast is sent to all local machines to search for hardware address of 172.16.10.1}

Address Resolution Protocol (ARP) cache of the host is check to see if the IP Address of the default gateway is resolved to MAC Address.

Once the data link layer has Packet and Destination Hardware access , LAN Driver is used to provide LAN Media Access (eg Ethernet). A Frame is generated.
Once completed , the frame is handed down to the Physical Layer to be put on Physical Medium (Cable , Wireless etc)
Every device on the Collision Domain gets the bits . If CRC matches , we got the match. If CRC does not match, frame is discarded.
Packet is pulled from the frame and handed over to the protocol specified in the ETHER type field.
IP gets the packet , checks IP Destination address . Packet does not have the address configured on router , the router looks for Destination address on the routing table.
- Routing Protocol is “rip”
Routing table must have 172.16.20.0 or packet will be discarded and an unreachable host (ICMP) will be issued.
- Sending updates every 30 seconds, next due in 17 seconds
- Invalid after 180 seconds, hold down 180, flushed after 240
- Redistributing: rip
- Default version control: send version 1, receive any version
- Interface Send Recv Triggered RIP Key-chain
- FastEthernet0/0 1 2 1
- FastEthernet1/0 1 2 1
- Automatic network summarization is in effect
- Maximum path: 4
- Routing for Networks:
- 172.16.0.0
- Passive Interface(s):
- Routing Information Sources:
- Gateway Distance Last Update
- Distance: (default is 120)
If entry is found , packet is switched to exit interface.
Ethernet 1 buffer has the packet . It now checks for PC1 MAC Address using ARP.
The data link layer creates a frame with the destination source (MAC) + FCS + Ether type field. This is sent to PC2.
PC2 checks for CRC Verification . PASSED! (Surprise Surprise!) . Packet is sent to the network layer.
Network layer IP Checks destination IP Match – Device whom the payload should be give to.
Payload is handed to ICMP. It now understands this is an echo request.