The Network Layer Forwarding –Internal path to follow Routing –External path to follow Models...

The Network Layer

• Forwarding– Internal path to follow

• Routing– External path to follow

• Models– Guaranteed delivery with or without bounded delay– In-order packet delivery– Guaranteed minimal bandwidth– Guaranteed maximum jitter

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Virtual Circuits

• Connection Oriented

• Connection state information

• Phases– VC Setup– Data Transfer– VC Teardown

Datagram Networks

• Internet

• Not connection oriented

• No guarantee of delivery

• Faster

Routing

• Address 129.123.3.0 Interface 0

• Address 129.123.7.0 Interface 1

• Address 129.123.7.40 Interface 2

• Address 129.123.63.0 Interface 3

• Address 129.123.73.0 Interface 4

Routers

Router Switching

Queueing

• Packet Scheduling

• Quality of Service

• Active Queue Management

Router Configuration

http://www.cs.usu.edu/~bobw/cs4720/CISCO.txt

• Lookup– Helper addresses

• Forwarding• Queueing• Other protocols

– IPX/SPX (Novell, Microsoft)– Appletalk (Macintosh)– DECnet (card readers)

Routing on the Internet

• RIP (Routing Internet Protocol)– Lots of traffic (advertisements)– Not very efficient– Basically obsolete

• OSPF (Open Shortest Path First)– Flooding– Secure– Multiple same cost paths– Multicast and Unicast capable

Router Monitoring

• Traceroute (tracert)– Simple routing test

• USU’s Web site for monitoring:http://pomoxis.usu.edu/~network/grapher.cgi?target=%2Fnetwork-devices%2Frouter-interfaces

• What’s UP

http://floyd.usu.edu

IP Network Communication

• IPv4 Addressing• Network Layer (IP, Layer 3)• Protocols are described in RFCs (Request for

Comments)• Available from nis.nsf.net/internet/documents/rfc• TCP/IP Addressing

– Class A (1-126).xxx.xxx.xxx– Class B (128-191).(assigned).xxx.xxx– Class C (192-223).(assigned).(assigned).xxx

Internet Addressing

• Each address is 4, 8 bit, decimal numbers• Like Area Code/Exchange/Subscriber• 129.123.7.170• 129.123 is assigned to USU (domain)• 172.xxx.xxx.xxx USU nonroutable• 7 is assigned to Computer Science• 170 is assigned to PC named java4• Every Internet device must have a number• Number to name conversion is done by DNS

IP header

• Version number (4 bits) – Tells router how to interpret datagram

• Type of Service – Selects delivery speeds vs. accuracy

• Datagram Length (16 bits) rarely longer than 1500 bytes• Identification, Flags and Fragment offset

– Reassembly of a fragmented datagram• Time to Live

– Router hops, control routing loops• Protocol (TCP,ICMP, UDP)• Header Checksum• Source and Destination IP addresses

Version Leng Type of Svc Total Length

Identification Flags Frag OffsetTime to Live Protocol Header Checksum

IP Header

Source Address

Destination Address

TCP Header then your data...

IP Fragmentation

• Not all routing systems utilize 1500 byte packets.

• PPP (dialup) sizes are 576 bytes.

• Like TCP frames, IP frames need to be reassembled in order even if one packet is lost.

IP Fragmentation

Subnets

• Class A 255.0.0.0

• Class B 255.255.0.0– USU uses 255.255.255.0 for subnetting

buildings

• Class C 255.255.255.0

• Subnet Masks– 129.123.0.0/16– 129.123.7.0/24

Flat vs. Routed Networks

• Flat network– Enormous party line– Systems move freely around enterprise– Simple and cheap to implement

• Routed network– Require subnetting– Control packet flow– Systems must readdress as they move

Subnetting

Obtaining a host address

• Number Assignment – (http://www.networksolutions.com)– Whois

• Number registration: http://thingy.usu.edu• Manual configuration

– Inserting IP numbers for subnet, router, nameserver• Dynamic Host Configuration Protocol

– Dynamic versus Static IP addressing– Discussed in next weeks presentation

ICMP

• Ping

• Router information

Network Address Translation (NAT)

• Protects internal systems– Makes internal systems invisible

• Recycles Internet Addresses (IP)

• Uses nonroutable IP addresses– 10.xxx.xxx.xxx– 172.xxx.xxx.xxx– 192.xxx.xxx.xxx

IP Version 6

Conversion to IPv6

• Addressing– 3ffe:ffff:0100:f101:0210:a4ff:fee3:9566 – Compatibility: ::ffff:w.x.y.z

• Dual Stack

• Tunneling

IPv6

• Extended address capabilities

• Streamlined header

• Flow labelling

• No fragmentation or reassembly

• No header checksum (redundant)

• No options

Broadcasting and Multicasting

• Uncontrolled Flooding– Copy of each packet to all neighbors– Can cause broadcast storms

• Controlled Flooding– Sequence number controlled flooding– Reverse path forwarding

• Spanning Trees

Multicasting

Types of Multicast Management Protocols

• Internet Group Management Protocol

• Distance-Vector Multicast Routing Protocol

• Protocol-Independent Multicast protocol

Applications of Multicast

• Online conferencing (mbone)– Video– Sound

• System Imaging– Symantec Ghost– Powerquest DriveImage

IP Layer

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