Fundamentals Of IP

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Cisco CCNA Study Guide	By Cbrzana
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Fundamentals of IP

Routing is synonymous with path selection.

Typical Features of Layer 3

• Defines routing and addressing
• PSI defines unique L3 protocol, Connectionless Network Services (CLNS)
• Other protocols include IP, IPX, AppleTalk Datagram Delivery Protocol (DDP)
• Routing Table contains list of network layer address groupings
• One entry per group, tells where to route packet next

Network Layer Interaction w/ Data Link Layer: Network layer analyzes packet, sends it to data link layer, data link layer adds appropriate header/trailer (Ethernet/HDLC/etc), Next router receives, strips header/trailer. Repeat process until destination reached.

ARP (Address Resolution Protocol): Used to dynamically learn data-link (MAC) address of an IP host.

IP - > MAC

Network Layer Addressing

• Network addresses
• TCP/IP = Network or subnet
• IPX = Network
• AppleTalk = Cable range
• Network ID labels network; Host ID labels specific member within that network
• Can have duplicate host IDs, as long as different network IDs

Protocol	Size (Bits)	Grouping Field (Bits)	Address Field (Bits)
IP	32	Network (8-30)	Host (2-24)
IPX	80	Network (32)	Node (48)
AppleTalk	24	Network (16)	Node (8)
OSI	Variable	Many formats	Domain-specific

'Routing Protocols ': End goal is to fill the routing table with all known destination groups and w/ the best route to reach each group.

• All IP addresses in same group must not be separated by router
• IP addresses separated by router must be in separate group

Classes of Networks

Class	1st Octet Range	# of Network Bytes	# of Host Bytes	# of Addresses per Network
A	1 -126	1	3	224 - 2
B	128 - 191	2	2	216 - 2
C	192 - 223	3	1	28 - 2

Reserved addresses = Network Address and Broadcast Address

Address Formats When Subnetting is Used

Network Layer Utilities

Domain Name System (DNS): Send DNS request, resolves IP address of machine

Address Resolution Protocol (ARP): Resolve MAC Address by sending ARP broadcast with specific IP

ICMP Echo: Used in ping command, computer tested replies w/ a ICMP echo reply.

Reverse ARP (RARP): Broadcast IP address, resolve ONLY the MAC Address

Boot Protocol (BOOTP): Broadcast IP address, resolve MAC Address, subnet mask, default gateway, other server IP addresses, and name of a file that should be downloaded

- > Main goal is to remotely booting an operating system

*Administration difficult for the above 2 because server had to know every MAC address of every computer.

Dynamic Host Control Protocol (DHCP): Dynamically assign IP from range of available IP addresses.

IP Routing Protocols: Includes subnet number, the interface which to forward packets (Serial, Ethernet, etc.), and the Next Hop IP Address.

• Dynamically learns and fills the routing table
• Place best route (if more than 1) in table
• Remove obsolete routes, add new routes.
• Time between losing a route and adding a new one = Convergence Time
• Try to prevent routing loops

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