CCNA Certification/Advanced Addressing Topics

Acknowledgements — Introduction — The OSI Model — Application Layer — Transport Layer — Network Layer — Addressing — Routing Protocols — Data Link Layer — Switching — Physical Layer — Router Operation — Advanced Addressing Topics — Advanced Routing Topics — Advanced Switching Topics — Security — WAN — Configuration — Conclusion — References — About the Exam — Cisco Router Commands — Quick Reference Sheet

Advanced Addressing Topics

IP Addressing
IPv4 Addressing Types
Subnetting
Variable Length Subnet Mask(VLSMs)
Network Address Translation
Internet Protocol Version 6 (IPv6)

Internet Protocol

Internet Protocol(IP) is basically the Internet layer. The other protocols in this layer exist to support the IP. IP uses the packet address and looks up the address in its routing table and decides where to send the packet by selecting the best possible path. 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. Each datagram is assigned the IP of the sender and of the recipient. Each router (layer-3 device) that receives a datagram makes routing decisions based on the packets destination I address.

An IP header is made up of the following fields.

Version: IP version number.
Header length: Header length (HLEN) in 32-bit words.
Priority and Type of Service: Type of Service tells how the datagram should be handled. The first 3 bits are the priority bits which is now called the differentiated service bits.
Total Length:- Length of the packet including header and data.
Flags: Specifies whether fragmentation and reassembly if the packet is too large to put in a frame. It allows different maximum transmission units (MTUs) on the internet.
Time To Live: The time to live is set into a packet when it is originally generated. If it doesn't get to where it wants to go before the before the TTl expires, the packet is dropped from the network. This stops IP packets from continuously circling the network looking for a home.
Protocol: Port of upper-layer protocol (TCP is port 6 or UDP is port 17). Also supports Network layer protocols, Like ARP and ICMP (this can be called Type Field in some analyzers).
Header Checksun: Cyclic redundancy check (CRC) on header only.
Source IP address: 32-bit IP address of the station this packet is destined for.
Destination IP address: 32-bit IP address of the station this packet is dstined for.
Options: Used for network testing, debugging, security, and more.
Data: After the IP option field will be the upper-layer data.

Network Address Translation

Network address translation (NAT) is used to connect hosts from a private network to the public internet.

Cisco NAT configuration require three settings:

Set one or more interfaces inside the private network

 Router(config) # interface FastEthernet 0/0
 Router(config-if)#ip nat inside

Set one or more interfaces outside the private network (i.e. the public internet).

Router(config) # interface Serial 0
Router(config-if) # ip nat outside

Set one or more ACLs for the NAT and indicate its type (static, dynamic, PAT, or overload).

ip nat inside source list 10 192.168.2.2 overload

References

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