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Chapter 6

NETWORK LAYER

Encapsulation, De-encapsulation, ip addressing, routing bu katmanda icra edilir.

Network layer protocols : IPv4, IPv6

IP is connectionless, meaning that no dedicated end-to-end connection is created before data is sent.

Unreliable or best-effort delivery characteristic of the IP protocol. The IP protocol does not guarantee that all packets that are delivered are, in fact, received.

IP operates independently of the media that carry the data at lower layers of the protocol stack.

Time-to-Live (TTL) - Contains an 8-bit binary value that is used to limit the lifetime of a packet. The packet sender sets the initial TTL value, and it is decreased by one each time the packet is processed by a router. If the TTL field decrements to zero, the router discards the packet and sends an Internet Control Message Protocol (ICMP) Time Exceeded message to the source IP address.

 

Router components :
CPU
IOS
flash : compressed IOS tutulur.
RAM : decompressed IOS, routing table, arp table, packet buffer, running-config
NVRAM : startup-config
ROM : limited IOS, POST, bootstrap
interface : ethernet, serial, console, aux

Router#show version
Cisco IOS Software, 1841 Software (C1841-ADVIPSERVICESK9-M), Version 12.4(15)T1, RELEASE SOFTWARE (fc2)
ROM: System Bootstrap, Version 12.3(8r)T8, RELEASE SOFTWARE (fc1)

System returned to ROM by power-on
System image file is "flash:c1841-advipservicesk9-mz.124-15.T1.bin"
Cisco 1841 (revision 5.0) with 114688K/16384K bytes of memory.
Processor board ID FTX0947Z18E
M860 processor: part number 0, mask 49
2 FastEthernet/IEEE 802.3 interface(s)
191K bytes of NVRAM.
63488K bytes of ATA CompactFlash (Read/Write)

Configuration register is 0x2102

Router#show ip interface brief
Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 192.168.1.254 YES manual up up

FastEthernet0/1 192.168.2.254 YES manual up up

Vlan1 unassigned YES NVRAM administratively down down

Router#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route

Gateway of last resort is not set

C 192.168.1.0/24 is directly connected, FastEthernet0/0
C 192.168.2.0/24 is directly connected, FastEthernet0/1

  • Router OSI' de layer 3 te çalışır.