l10: simple internetworking - github pages · l10: simple internetworking huichen, ph.d. department...
TRANSCRIPT
![Page 1: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/1.jpg)
L10: Simple
Internetworking
Hui Chen, Ph.D.
Department of Engineering & Computer Science
Virginia State University
Petersburg, VA 23806
9/26/2016 1CSCI 445 – Fall 2016
![Page 2: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/2.jpg)
Acknowledgements
� Some pictures used in this presentation were obtained from
the Internet
� The instructor used the following references
� Larry L. Peterson and Bruce S. Davie, Computer Networks: A Systems
Approach, 5th Edition, Elsevier, 2011
� Andrew S. Tanenbaum, Computer Networks, 5th Edition, Prentice-
Hall, 2010
� James F. Kurose and Keith W. Ross, Computer Networking: A Top-
Down Approach, 5th Ed., Addison Wesley, 2009
� Larry L. Peterson’s (http://www.cs.princeton.edu/~llp/) Computer
Networks class web site
9/26/2016 CSCI 445 – Fall 2016 2
![Page 3: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/3.jpg)
Outline
� Topic: internetworking
� Case study: Internet Protocol (IP) Suite
� Simple interworking
� internet and the Internet
� Global addressing scheme
� Packet fragmentation and assembly
� Best effort service model and datagram forwarding
� Address translation
� Host configuration
� Error reporting
9/26/2016 3CSCI 445 – Fall 2016
![Page 4: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/4.jpg)
Heterogeneity and Scalability
� LAN: small in size
� How to extend LAN?
� Bridges and switches
� Good for global networks?
� Spanning tree algorithms � very long path and huge forwarding tables
� Bridges and switches: link level/layer 2 devices � networks must be using the same type of links
� Problems to deal with
� Scalability: global networks are huge in size
� Heterogeneity: networks of different types of links are in use
9/26/2016 4CSCI 445 – Fall 2016
![Page 5: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/5.jpg)
Network of Networks:
internetworking
5CSCI 445 – Fall 2016
9/26/2016
� An arbitrary collection of networks interconnected to provide some sort of
host-host to packet delivery service
![Page 6: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/6.jpg)
Solution to Scalability: Network of
Networks
� Forwarding packets to networks from networks: smaller forwarding tables
9/26/2016 6CSCI 445 – Fall 2016
![Page 7: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/7.jpg)
Solution to Heterogeneity: layered
architecture and hourglass design
9/26/2016 CSCI 445 – Fall 2016 7
� Network layer encapsulates the heterogeneity and the complexity of data link and physical layers (or the host-to-network layer)
![Page 8: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/8.jpg)
Network Layer and Lower Layers
Link Layer(type 1)
Link Layer(type 2)
Network layer
Adapter
OSNetwork layer packet
Network layer packet as payload
Route
r
9/26/2016 8CSCI 445 – Fall 2016
![Page 9: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/9.jpg)
Internet Protocol
9CSCI 445 – Fall 2016
9/26/2016
� IP = Internet Protocol
� Key tool used today to build scalable, heterogeneous internetworks
� Routers forward packets to “networks”: forwarding tables can be smaller
� Above link layer: can cope with different link layer technology
� Runs on all the nodes in a collection of networks
� Defines the infrastructure
� Allows these nodes and networks to function as
a single logical internetwork
![Page 10: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/10.jpg)
Case Study: The Internet
� Global internetworks built on IP � The Internet ≠ internet
� Using Internet Protocol (IP) as a case study
� Datagram forwarding and service model
� IP packet format and global IP addressing scheme
� Deal with Link layer and network layer interfacing
� Packet fragmentation and assembly
� Address translation
� Other important issues
� Host configuration
� Error reporting
9/26/2016 10CSCI 445 – Fall 2016
![Page 11: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/11.jpg)
IP Service Model
� Packet Delivery Model
� Connectionless model for data delivery
� Best-effort delivery (unreliable service)
� packets may be lost
� packets may be delivered out of order
� duplicate copies of a packet may be delivered
� packets may be delayed for a long time
� Global Addressing Scheme
� Provides a way to identify all hosts in the network
9/26/2016 CSCI 445 – Fall 2016 11
![Page 12: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/12.jpg)
Basic Data Structure: IP Packet
� Design Goals
� Attributes and purposes
� Support error detection and handling
� Support networks as a forwarding source and destinations
� Support different networking technologies
� Support multiplexing
� Support extensibility
9/26/2016 CSCI 445 – Fall 2016 12
![Page 13: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/13.jpg)
IP Packet Format (1)
� Discussing IP version 4 (IPv4). Discussing IP version
6in later lessons
� Convention used to illustrate IP packet
� 32 bit words
� Top word transmit first
� Left-most byte transmit first
9/26/2016 13CSCI 445 – Fall 2016
![Page 14: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/14.jpg)
Packet Format
� Version (4): 4 or 6. The rest is for version 4. Discussing 6 in later lessons
� Hlen (4): number of 32-bit words in header
� TOS (8): type of service (not widely used)
� Length (16): number of bytes in this datagram
� Ident (16): used by fragmentation
� Flags/Offset (16): used by fragmentation
� TTL (8): number of hops this datagram has traveled
� Protocol (8): demux key (TCP=6, UDP=17)
� Checksum (16): of the header only
� DestAddr & SrcAddr (32)
9/26/2016 CSCI 445 – Fall 2016 14
![Page 15: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/15.jpg)
Capturing an IP Packet
� And examining it …
� Use the ethercap application (a part of homework 1)
� Use Wireshark
� Use Microsoft Network Monitor (Message Analyzer)
� Use tcpdump
� Use libpcap in your own application
� ……
9/26/2016 CSCI 445 – Fall 2016 15
![Page 16: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/16.jpg)
Using Wireshark
9/26/2016 16CSCI 445 – Fall 2016
![Page 17: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/17.jpg)
IP Packet
DATAIP Header
DATA
DATAIP HeaderLink Layer Header
9/26/2016 17CSCI 445 – Fall 2016
![Page 18: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/18.jpg)
A Captured IP Packet
9/26/2016 18CSCI 445 – Fall 2016
![Page 19: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/19.jpg)
Ethernet Protocol Numbers
9/26/2016 19CSCI 445 – Fall 2016
![Page 20: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/20.jpg)
Exercise L10-1
� Below shows a captured
Ethernet frame
� Q1: what is the length in bytes
of the largest IP packet?
� Q2: what is the length in bytes
of the smallest IP packet?
� Q3: what are the values (bits) of
each field in the IP packet below
(underlined). Which byte is the
last byte of this IP packet?
9/26/2016 CSCI 445 – Fall 2016 20
![Page 21: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/21.jpg)
IP Fragmentation and Reassembly
� Each network has some MTU (Maximum Transmission Unit)� Ethernet (1500 bytes), FDDI (4500 bytes)
� Strategy� Fragmentation occurs in a router when it receives a
datagram that it wants to forward over a network which has (MTU < datagram)
� Reassembly is done at the receiving host
� All the fragments carry the same identifier in the Identfield
� Fragments are self-contained datagrams
� IP does not recover from missing fragments
9/26/2016 CSCI 445 – Fall 2016 21
![Page 22: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/22.jpg)
IP Fragmentation and Reassembly:
Example
� IP packet
� Data: 1400 bytes
� IP header: 20 bytes
� MTU
� Ethernet=1500
� FDDI=4500
� PPP=532
9/26/2016 CSCI 445 – Fall 2016 22
![Page 23: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/23.jpg)
Example
MTU=1500 MTU=4500 MTU=532 MTU=1500
IP packet at H1Data: 1400 bytesIP header: 20 bytes
9/26/2016 23CSCI 445 – Fall 2016
![Page 24: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/24.jpg)
Bit 0: reserved, must be zero Bit 1: (DF) 0 = May Fragment, 1 = Don't Fragment. Bit 2: (MF) 0 = Last Fragment, 1 = More Fragments.Source: http://www.freesoft.org/CIE/Course/Section3/7.htm
IP packet begins
IP packet ends
9/26/2016 24CSCI 445 – Fall 2016
![Page 25: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/25.jpg)
Example
Ident:Same across all fragmentsUnique for each packet
MF (More Fragments) bit in Flags:
set � more fragments to follow0 � last fragment
Offsetin 8-byte chunks
Fragmented into three fragments
Q: why 8-byte chunks?
9/26/2016 25CSCI 445 – Fall 2016
![Page 26: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/26.jpg)
Hint for “Why 8-byte Chunk?”
9/26/2016 26CSCI 445 – Fall 2016
![Page 27: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/27.jpg)
IP Fragmentation and Reassembly
� IP datagrams traversing the sequence of physical networks
9/26/2016 CSCI 445 – Fall 2016 27
![Page 28: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/28.jpg)
Exercise L10-2
� For an imaginary network below
MTU=1800 MTU=1500 MTU=512 MTU=256
� Q: H1 sends an IP packet of 1800 bytes including IP header to H8. Please
show
1. IP datagrams traversing the sequence of physical networks graphed
above
2. Header fields of IP datagrams before entering and after leaving each
router and hosts
9/26/2016 28CSCI 445 – Fall 2016
![Page 29: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/29.jpg)
Implementation of Reassembly
� Hints to understand the program (pp.243-247)
Instance of FragInfo
Instance of FragInfo
Instance of FragInfo
TAILHEAD
Instance of FragInfo
Instance of FragInfo
Instance of FragInfo
TAILHEAD
Instance of FragInfo
Instance of FragInfo
Instance of FragInfo
TAILHEAD
…
…
…
Map
KEY
KEY
KEY
Not necessarily a linked list
Instance of FragList: fragments of an unfragmented packet
One fragment
9/26/2016 29CSCI 445 – Fall 2016
![Page 30: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/30.jpg)
Global Addresses
� Internet Protocol (IP) Address
� Globally unique
� hierarchical: network + host
� IPv4� 4 Billion IPv4 addresses, half are A type, ¼ is B type, and
1/8 is C type
� 32 bit integer
� Human-readable form: IPv4 numbers-and-dots notation� 150.174.44.57
� Facing exhaustion of address space, moving to IPv6
9/26/2016 30CSCI 445 – Fall 2016
![Page 31: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/31.jpg)
IPv4 Address Classes (Legacy)
� Classes (legacy)
� To express networks
9/26/2016 CSCI 445 – Fall 2016 31
Network Host
7 24
0A:
Network Host
14 16
1 0B:
Network Host
21 8
1 1 0C:
Classes
![Page 32: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/32.jpg)
Broadcast and Multicast Addresses
� Do the classes of IP addresses discussed including
any IP addresses starting with bits 111?
Network Host
7 24
0A:
Network Host
14 16
1 0B:
Network Host
21 8
1 1 0C:
Classes
9/26/2016 32CSCI 445 – Fall 2016
![Page 33: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/33.jpg)
IPv4 Multicast Address
� Addresses starting with 1110
9/26/2016 CSCI 445 – Fall 2016 33
Network Host
7 24
0A:
Network Host
14 16
1 0B:
Network Host
21 8
1 1 0C:
Classes
Group Address1 1 01Multicast Address
![Page 34: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/34.jpg)
IPv4 Broadcast Address
� setting all the host bits to 1
9/26/2016 CSCI 445 – Fall 2016 34
Network 1111…11111
7 24
0A:
Network 111…111
14 16
1 0B:
Network 1…1
21 8
1 1 0C:
Classes
![Page 35: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/35.jpg)
IPv4 Address Spaces for Private
Networks
� See RFC 1918
� Private networks
� 24-bit block 10.0.0.0–10.255.255.255
� 20-bit block 172.16.0.0–172.31.255.255
� 16-bit block 192.168.0.0–192.168.255.255
9/26/2016 35CSCI 445 – Fall 2016
![Page 36: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/36.jpg)
Link Local IPv4 Address
� See RFC 3927
� Link-Local IPv4 Address
� 16-bit block 169.254.0.0–169.254.255.255
9/26/2016 CSCI 445 – Fall 2016 36
![Page 37: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/37.jpg)
Exercise L10-3
� Find out IPv4 addresses of following hosts and indicate the class to which the IP addresses belong
� www.vsu.edu
� www.drsr.sk
� www.google.com
� Remark
� There are many ways to find out the IP address of a host given a domain name
� Example: nslookup www.vsu.edu (which works on most platforms including Windows, Unix/Linux, and Mac OS X)
� Convert the first number (from left) to a binary number, then take a look at the 1st, and/or 2nd, and/or 3rd bit
9/26/2016 37CSCI 445 – Fall 2016
![Page 38: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/38.jpg)
IP Datagram Forwarding
� Strategy� every datagram contains destination's address
� if directly connected to destination network, then forward to host
� if not directly connected to destination network, then forward to some router
� forwarding table maps network number into next hop
� each host has a default router
� each router maintains a forwarding table
9/26/2016 CSCI 445 – Fall 2016 38
![Page 39: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/39.jpg)
Forwarding Table: Example
� Forwarding table at router R2 that has two interfaces
0 and 1
9/26/2016 CSCI 445 – Fall 2016 39
01
![Page 40: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/40.jpg)
Forwarding Algorithm
�Algorithm
if (NetworkNum of destination = NetworkNum of one of my interfaces) then
deliver packet to destination over that interface
else
if (NetworkNum of destination is in my forwarding table) then
deliver packet to NextHop router
else
deliver packet to default router
9/26/2016 CSCI 445 – Fall 2016 40
![Page 41: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/41.jpg)
Forwarding Algorithm
�For a host with only one interface and only a default router in its forwarding table, this simplifies to
if (NetworkNum of destination = my NetworkNum)then
deliver packet to destination directly
else
deliver packet to default router
9/26/2016 CSCI 445 – Fall 2016 41
![Page 42: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/42.jpg)
Exercise L10-4
� Construct forwarding tables for routers R1 and R3.
Interfaces of routers are marked
9/26/2016 42CSCI 445 – Fall 2016
011
0
1
0
![Page 43: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/43.jpg)
IP address to Physical Address
Translation
� Questions:
� In an IP network, an IP packet is the payload of one or more Ethernet
frames. Who prepares the Ethernet frame headers which contain
destination Ethernet/physical address of the destination node?
� How does the source node know the Ethernet/physical address of the
destination node?
Link LayerEthernet MAC
00:1E:C9:2E:F4:6D
Network layerIP = 150.174.2.101
Adapter
OS IP packet
IP packet as payload
9/26/2016 43CSCI 445 – Fall 2016
![Page 44: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/44.jpg)
Map IP Addresses into Physical
Addresses
� Map IP addresses into physical addresses
� destination host
� next hop router
� Techniques
� encode physical address in host part of IP address
� table-based
� ARP (Address Resolution Protocol)
� table of IP to physical address bindings
� broadcast request if IP address not in table
� target machine responds with its physical address
� table entries are discarded if not refreshed
9/26/2016 CSCI 445 – Fall 2016 44
![Page 45: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/45.jpg)
ARP Packet Format
� An ARP packet is the payload of a frameEthernet Header ARP Packet
DST SRC Type
0x0806
9/26/2016 45CSCI 445 – Fall 2016
![Page 46: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/46.jpg)
ARP Packet Format� HardwareType: type of physical network (e.g., Ethernet)
� ProtocolType: type of higher layer protocol (e.g., IP)
� HLEN & PLEN: length of physical and protocol addresses
� Operation: request or response
� Source/Target Physical/Protocol addresses
9/26/2016 CSCI 445 – Fall 2016 46
![Page 47: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/47.jpg)
ARP Packet: Examples
Ethernet Header ARP Packet
DST SRC Type
0x0806Operation (opcode)
•1 request•2 reply•3 request reverse•4 reply reverse
9/26/2016 47CSCI 445 – Fall 2016
![Page 48: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/48.jpg)
ARP: Discussion
� Prevent stalled entries� Table entries will timeout (~15 minutes)
� Do not refresh table entries upon reference
� Fresh entries (reset timer)� Update table if already have an entry
� Reduce ARP messages� Update table with source when you are the target in ARP
request messages
9/26/2016 CSCI 445 – Fall 2016 48
![Page 49: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/49.jpg)
ARP Table in Practice (1)
9/26/2016 49CSCI 445 – Fall 2016
![Page 50: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/50.jpg)
ARP Table in Practice (2)
9/26/2016 50CSCI 445 – Fall 2016
![Page 51: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/51.jpg)
Host Configuration
� Ethernet addresses are configured into network by
manufacturer and they are unique
� IP addresses must be unique on a given internetwork
but also must reflect the structure of the
internetwork
� Most host Operating Systems provide a way to
manually configure the IP information for the host
� Drawbacks of manual configuration
� A lot of work to configure all the hosts in a large network
� Configuration process is error-prune
� Automated Configuration Process is required9/26/2016 51CSCI 445 – Fall 2016
![Page 52: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/52.jpg)
Dynamic Host Configuration
Protocol (DHCP)
� DHCP server is responsible for providing
configuration information to hosts
� There is at least one DHCP server for an
administrative domain
� DHCP server maintains a pool of available addresses
9/26/2016 CSCI 445 – Fall 2016 52
![Page 53: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/53.jpg)
DHCP
� Newly booted or
attached host sends
DHCPDISCOVER
message to a special
IP address
(255.255.255.255)
� DHCP relay agent
unicasts the message
to DHCP server and
waits for the
response9/26/2016 CSCI 445 – Fall 2016 53
![Page 54: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/54.jpg)
Internet Control Message Protocol
(ICMP)
� Defines a collection of error messages that are sent back to the source host whenever a router or host is unable to process an IP datagram successfully� Destination host unreachable due to link /node failure
� Reassembly process failed
� TTL had reached 0 (so datagrams don't cycle forever)
� IP header checksum failed
� ICMP-Redirect � From router to a source host
� With a better route information
9/26/2016 CSCI 445 – Fall 2016 54
![Page 55: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/55.jpg)
Virtual Networks and Tunnels
� Internetworks often have shared infrastructure
networks
� Data packets may not be forwarded without
restriction
� Virtual Private Networks (VPN)
� VPN is a heavily overused and definitions vary
� An “private” network utilizing an shared network
infrastructure
9/26/2016 CSCI 445 – Fall 2016 55
![Page 56: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/56.jpg)
Virtual Private Networks: Example
� Corporations X and Y want their own networks via “leased lines” belonging to other networks
� X wants to keep their data private
� So does Y
� X and Y have “virtual” private networks
� “virtualization” can be done on different layers
� Layer 2 VPN
� Layer 3 VPN
9/26/2016 56CSCI 445 – Fall 2016
![Page 57: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/57.jpg)
Virtual Private Networks via IP Tunneling
Network 2
Network 3
Office in London
Office in LA
Office in NYC
Pre-configured tunnel
9/26/2016 57CSCI 445 – Fall 2016
Forwarding Table at R1
![Page 58: L10: Simple Internetworking - GitHub Pages · L10: Simple Internetworking HuiChen, Ph.D. Department of Engineering & Computer Science ... Approach, 5th Edition, Elsevier, 2011 Andrew](https://reader035.vdocuments.net/reader035/viewer/2022070709/5ec0f99142dbeb2a83002ed1/html5/thumbnails/58.jpg)
Summary
� internet and the Internet
� Global addressing scheme
� Packet fragmentation and assembly
� Best effort service model and datagram forwarding
� Address translation
� Host configuration
� Error reporting
9/26/2016 58CSCI 445 – Fall 2016