1. Routing Fundamentals and Subnetting
Module 10
Routing Fundamentals and Subnetting

2. Routable Protocols
A protocol is a set of rules that determines how computers communicate with each other across networks
A protocol describes the following:
The format that a message must conform to
The way in which computers must exchange a message within the context of a particular activity

3. Routed Protocols
A routed protocol allows the router to forward data between nodes on different networks.
it must have the ability to assign a network number and a host number to each individual device
These protocols also require a network mask (subnet mask) in order to differentiate between the network and host portion of the address.

4. Routable Protocols

5. Encapsulation Process
Data
Segments
Packets
Frames
Bits

6. Transport Layer

7. Internet Protocol (IP)
The Internet Protocol (IP) is the most widely used network-addressing scheme
IP is a connectionless, unreliable, best-effort delivery protocol
IP does not verify that the data reaches its destination; this function is handled by the upper layer protocols

8. IP
Data is encapsulated into packets, also known as datagrams at the network layer of the OSI model.

9. Connection-Oriented vs. Connectionless Networks
Often referred to as packet-switched processes
IP Protocol
Internet
Connection-Oriented Networks
Often referred to as circuit-switched processes
A connection with the recipient is first established, and then data transfer begins
TCP adds Layer 4, connection-oriented reliability services to IP

10. IP Header
IP header length (HLEN) – Indicates the datagram header length in 32-bit words.
Padding – extra zeros are added to this field to ensure that the IP header is always a multiple of 32 bits.
Flags – A three-bit field in which the two low-order bits control fragmentation

11. Network Layer Routing is an OSI Layer 3 function
Routing is the process of finding the most efficient path from one device to another
The primary device that performs the routing process is the router

12. Routers
A router is a network layer device that uses one or more routing metrics to determine the optimal path along which network traffic should be forwarded
Routers make logical decisions regarding the best path for the delivery of data
Routing metrics are values used in determining the advantage of one route over another

13. Routers
The encapsulation and de-encapsulation process occurs each time a packet transfers through a router
This process breaks up the data stream into segments, adds the appropriate headers and trailers then transmits the data. The de-encapsulation process is the opposite process, removing the headers and trailers, then recombining the data into a seamless stream

14. Routing versus Switching
Switching occurs at Layer 2 of the OSI model
Routing occurs at Layer 3
The Layer 2 switch can only recognize its own local MAC addresses and cannot handle Layer 3 IP addresses
A Layer 2 switch interconnects segments belonging to same logical network or subnetwork

15. Routing versus Switching

16. Routing versus Switching
Each computer and router interface maintains an ARP table for Layer 2 communication. The ARP table is only effective for the broadcast domain (or LAN) that it is connected to.
The router also maintains a routing table that allows it to route data outside of the broadcast domain
Each ARP table contains an IP-MAC address pair

17. Routing versus Switching
The Layer 2 switch can only recognize its own local MAC addresses and cannot handle Layer 3 IP addresses
When a host has data for a non-local IP address, it sends the frame to the closest router also known as its default gateway
The host uses the MAC address of the router as the destination MAC address

18. Routing versus Switching
Another difference between switched and routed networks is switched networks do not block broadcasts
Routers block LAN broadcasts
Because routers block broadcasts, routers also provide a higher level of security and bandwidth control than switches

19. Routed versus Routing Protocols
Routed protocols transport data across a network
Examples of routed protocols include:
Internet Protocol (IP)
Novell's Internetwork Packet Exchange (IPX)
DECnet
AppleTalk
Xerox Network Systems (XNS)

20. Routed versus Routing Protocols
Routing protocols allow routers to choose the best path for data from source to destination
Routers use routing protocols to exchange routing tables and share routing information
Routing protocols enable routers to route routed protocols
Examples of routing protocols include:
Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), and Enhanced IGRP (EIGRP).

21. Path Determination Path determination occurs at the network layer
It enables a router to compare the destination address to the available routes in its routing table, and to select the best path
The routers learn of these available routes through static routing or dynamic routing
Routes configured manually by the network administrator are static routes
Routes learned by others routers using a routing protocol are dynamic routes
Each router that the packet encounters along the way is called a hop. The hop count is the distanced traveled

22. Routing Tables
Routers use routing protocols to build and maintain routing tables that contain route information
Routers keep track of important information in their routing tables, including the following:
Protocol type – The type of routing protocol that created the routing table entry
Destination/next-hop associations
Routing metric
Outbound interfaces
Routers communicate with one another to maintain their routing tables through the transmission of routing update messages

23. Routing algorithm and metrics
Routing protocols often have one or more of the following design goals:
Optimization
Simplicity and low overhead
Robustness and stability
Flexibility
Routing algorithms use different metrics to determine the best route. The most commonly used metrics include:
Bandwidth Delay
Load Reliability
Hop count
Ticks
Cost

24. IGPs and EGPs
Two types of routing protocols are Interior Gateway Protocols (IGPs) and Exterior Gateway Protocols (EGPs)
IGPs route data within an autonomous system.
EGPs route data between autonomous systems

25. IGPs and EGPs Examples of IGPs include:
Routing Information Protocol (RIP) and (RIPv2)
Interior Gateway Routing Protocol (IGRP)
Enhanced Interior Gateway Routing Protocol (EIGRP)
Open Shortest Path First (OSPF)
Intermediate System-to-Intermediate System Protocol (IS-IS)
An example of EGP is:
Border Gateway Protocol (BGP)

26. Link State and Distance Vector
IGPs can be further categorized as either distance-vector or link-state protocols
Distance-vector routing determines the distance and direction to any link in the internetwork
Routers using distance-vector algorithms send all or part of their routing table entries to adjacent routers on a periodic basis
Link-state algorithms typically use their databases to create routing table entries that prefer the shortest path
Link-state routing protocols respond quickly to network changes sending trigger updates only when a network change has occurred

27. Distance-vector Routing Protocols
Examples of distance-vector protocols include:
Routing Information Protocol (RIP) – The most common IGP in the Internet, RIP uses hop count as its only routing metric. RIP cannot route a packet beyond 15 hops.
Interior Gateway Routing Protocol (IGRP) – This IGP was developed by Cisco to address issues associated with routing in large, heterogeneous networks. IGRP can select the fastest available path based on delay, bandwidth, load, and reliability. IGRP also has a much higher maximum hop count limit than RIP.
Enhanced IGRP (EIGRP) – This Cisco-proprietary IGP includes many of the features of a link-state routing protocol. EIGRP provides superior operating efficiency such as fast convergence and low overhead bandwidth Because of this, it has been called a balanced-hybrid protocol, but it is really an advanced distance-vector routing protocol

28. Link-State Routing Protocols
Examples of link-state protocols include:
Open Shortest Path First (OSPF)
Intermediate System-to-Intermediate System (IS-IS). used for routed protocols other than IP

29. Subnetting
Subnetting provides manageability, enables the network administrator to provide broadcast containment, and low-level security on the LAN.
Subnet addresses include the Class A, Class B, and Class C network portion, plus a subnet field and a host field. The subnet field and the host field are created from the original host portion of the major IP address.
A LAN is seen as a single network with no knowledge of the internal network structure. This view of the network keeps the routing tables small and efficient.

30. Subnet Mask
The subnet mask gives the router the information required to determine in which network and subnet a particular host resides
The subnet octet or octets are determined by adding the position value of the bits that were borrowed. If three bits were borrowed, the mask for a Class C address would be
This mask may also be represented, in the slash format, as /27. The number following the slash is the total number of bits that were used for the network and subnetwork portion.

31. Subnetting Formula
Number of usable subnets equals two to the power of the assigned subnet bits or borrowed bits, minus two (reserved addresses for subnetwork id and subnetwork broadcast)
2 power of borrowed bits –2 = usable subnets
23 = = 6 usable subnets
Number of usable hosts equals two to the power of the bits remaining, minus two (reserved addresses for subnet id and subnet broadcast)
2 power of remaining host bits –2 = usable hosts
25 = 32 – 2 = 30 usable hosts per subnet

32. ANDing Process
Routers use subnet masks to determine the home subnetwork for individual nodes. This process is referred to as logical ANDing.
ANDing is a binary process by which the router calculates the subnetwork ID for an incoming packet.