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Chapter 10
IP
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Packet-switching
Connectionless
Unreliable
Best-effort delivery
Depends on TCP to provide error checking and
reliability
Benefits of Subnetting
• Creates smaller broadcast domains
• Provides low-level security
• Increases address flexibility
Layer 3 Device
• Router
• provides end-to-end packet
delivery services to its user, the
transport layer
• Makes best path determination
based on IP addressing
• Strips off Layer 2 source
addresses and replace them with
its OWN Layer 2 source address
when forwarding a packet.
Routers
• Do not forward broadcast or multicast frames
• Forward packets based on the Layer 3 header information.
• Can limit or secure network traffic based on identifiable
attributes within each packet.
• Switch packets to the appropriate interface based on the
destination IP address.
• Can perform bridging and routing.
Layer 3 Packet/Datagram
VERS
HLEN
Service Type
Total Length
IdentificationPrevents routing
Flags
Fragment Offset
Time to Live Protocol loops Header Checksum
Source IP Address
Destination IP Address
IP Options (if any)
Data
Padding
Layer 3 Devices
• Routers
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Interconnect network segments or entire networks.
Make logical decisions based on IP addresses.
Determines best path for data on an internetwork.
Create broadcast domains
Path Determination
• The process the router uses to choose the
next hop in the path the packet travels.
• The router uses the network address to
identify the destination network of a packet
within an internetwork.
• IP addresses can be assigned by a network
administrator or automatically (dynamically.)
Broadcast Addresses
• Broadcast Address – is used to send data to all of the
devices on a network.
• Broadcast IP addresses end with binary 1s in the host
part of the address.
• Class B Broadcast Address example:
• 176.10.255.255
(Remember decimal 255 = binary 11111111)
BINARY ANDING
• This is the process that routers use to determine the network or
subnetwork portion of an IP address using the address and the
subnet mask
• Both digits must be ones in order for the result to be a one.
Layer 3 Protocols
• IP
• Internet Protocol
• ARP
• Address Resolution Protocol
• ICMP
• Internet Control Message Protocol
DHCP Process
• Requires DHCP server on network
• Initializes on computer start-up
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Sends DHCP discover
Server responds with a DHCP offer
Host responds with a DHCP request
Server responds with DHCP ack
Default Gateway
• A default gateway is the IP address of the interface on the router
that connects to the network segment that it needs.
• The default gateway’s IP address must be in the same network
segment as the host is on.
Routed Protocols
• Provide packet switching and packet forwarding
between hosts (end system to end system)
• Bases decisions on logical addresses
• Examples
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IP
IPX
Appletalk
XNS
DECnet
NetBEUI
• Non-routable layer 3 protocol
• Small, fast, efficient
• Only works on the same network segment
Router Interfaces
• Routers connect separate networks
• Each of the connections to those network is called interface or port
• Each interface must have its own IP address
Routing Protocol
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Maintains a routing table
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Routing tables include
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Table of routes to network destinations and metrics to those destinations
Shares routing tables between
Protocol(s) used
Metrics
Networks
Outbound interfaces
Examples:
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RIP (Routing Information Protocol) – distance vector
IGRP (Interior Gateway Routing Protocol) – distance vector
OSPF (Open Shortest Path First) – link state
EIGRP (Enhanced IGRP) - hybrid
IS-IS (Intermediate System to Intermediate System) – link state
Metric
• A measurement
• Used by routing protocols to determine the best
path to a destination
• Examples:
• RIP – hop count
• IGRP – bandwidth, load, reliability, delay
Routed vs. Routing Protocols
• Routed protocols are routed by routing
protocols.
RIP
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Distance vector routing protocol
Metric: hop count
Max: 15 hops
Routing table updates every 30 seconds