CSC ECE 573 HW1 file Users douglas Reeves Classes csc573 2005 20fall website h CSC ECE 573 Internet Protocols Fall 2005 Homework 1 Home Syllabus Calendar Homework Project Message Board Exams Links Due Date Tuesday August 30 at 11 45 PM Instructions Homeworks should be submitted individually We will use the standard submit utility for our class to submit all work which means your work must be prepared electronically Put your name the assignment number and date at the top of the first page Put solutions in order don t make the TA hunt for your solution Do not plagiarize that means do not copy content from any source without permission from the instructor and if permitted acknowledge the source Problems 1 Compute a checksum as the ones complement sum of the following 8 bit words 1 through 4 and then ones complement that sum Show the 8 bit result 00100000 10001011 01001101 01000100 Will an error in the rightmost bit of both word 2 and word 3 be detected How about an error in the leftmost bit of word 2 2 An IP packet without options is to be sent across a link with MTU 760 Some of the fields of this packet s header before fragmentation are shown below This packet also includes a 8 byte UDP header immediately after the IP header Show what these fields are for each fragment and indicate where and in what fragment s the UDP header will appear Header Length 5 Total Length 3000 Identification 25335 Flags DF 0 MF 0 Fragment Offset 0 3 Indicated below is a path through a network from host A to host B Show what is recorded in the IP Source Route Option header before sending this packet and after receiving this packet if strict source routing is used to follow this path The path is Host A 192 168 10 98 First router incoming interface 192 168 10 94 outgoing interface 192 168 22 90 Second router incoming interface 192 168 22 86 outgoing interface 192 168 35 86 Third router incoming interface 192 168 35 83 outgoing interface 192 168 46 80 Host B 192 168 46 75 4 Decode the following IP header shown in hexadecimal and state clearly in decimal or in words what each field value means 45 00 00 28 c1 e8 00 00 e3 06 49 7b 98 01 02 f4 98 0e 3e 69 5 Layering like modularity is a way for people to deal with complexity and as such seems like a good idea What is an example of a networking function where you might want or need to violate the layering principle Justify your answer with a few sentences 6 Do a little web research and find what of IP datagrams are fragmented in practice Cite your source CAIDA tends to be a good first place to look for data about the Internet 7 Using http www ietf org iesg 1rfc index txt create a table showing how many RFC s were adopted in the 60 s 70 s combine these the 80 s the 90 s and so far in the 00 s Don t worry about missing or unused numbers What do you conclude about the rate of standards development 1 of 3 7 18 07 3 32 PM CSC ECE 573 HW1 file Users douglas Reeves Classes csc573 2005 20fall website h 8 RFC 1958 Architectural Principles of the Internet is an entertaining and opinionated compilation of IETF philosophy One statement from there is Be strict when sending and tolerant when receiving What does this mean and are there any undesirable consequences of adopting this policy in implementing protocols 9 I ran netstat s on machine remote linux eos ncsu edu and got the following partial output Ip 1954212 total packets received 0 forwarded 0 incoming packets discarded 936300 incoming packets delivered 1402038 requests sent out 1020093 reassemblies required 276206 packets reassembled ok 27989 fragments received ok 107619 fragments created Icmp 2941 ICMP messages received 0 input ICMP message failed ICMP input histogram destination unreachable 65 timeout in transit 1 echo requests 2857 echo replies 18 2857 ICMP messages sent 0 ICMP messages failed ICMP output histogram echo replies 2857 Tcp Udp TcpExt From this data does it appear that fragmentation occurs very frequently 10 From your computer use the tracert command traceroute on linux to find the longest path largest number of hops you can to any IP address in the world be creative What is this destination and how many hops did it take to reach this destination from your machine Note geographic distance does not always correlate with number of hops 11 Is there anything wrong with multiple IP addresses mapping to the same MAC address on an Ethernet Why or why not 12 Is there anything wrong with multiple MAC addresses on an Ethernet mapping to the same IP address Why or why not 13 On the Homework website is a dump file captured by ethereal Download and install ethereal on your own machine and process this file to answer a few questions The Ethereal Help function by the way is not very good I recommend instead looking at the online documentation at http www ethereal com docs Note 2 If you click Expression beside Filter you ll get a list of the keywords that can be used in filters How many packets are in this dump file use Statistics Summary How long a period of time does this dump represent How many are IP datagrams How many are DNS messages How many are ARP packets Why are there so many ARP Requests in this dump but so few ARP Replies Sort by protocol just click on the Protocol column and list all the protocols you find in packets sent during this short window of time There s a lot going on in networks isn t there 14 Take a look at http www rootsecure net content downloads pdf downloads arp spoofing intro pdf Using ARP what are two ways a host X attached to an Ethernet switch can make sure it receives all Ethernet frames sent by another host Y attached to the same Ethernet switch 15 The linux networking source code can be found at http lxr linux no source net which links together source files in a convenient to browse way Files specific to IPv4 are in folder ipv4 The source code is difficult to read line for line unless you really study the entire networking subsystem thoroughly Nevertheless I d like for you to get comfortable looking for things in source code and at least scanning for answers to specific questions Attempt to answer at least two of the following questions ask me the TA or another student for help if you need it If multiple replies to ARP request which one used see arp c If option should not be included in successive fragments what does linux do see ip options c 2 of 3 7 18 07 3 32 PM CSC ECE 573 HW1 file Users douglas Reeves Classes csc573 2005 20fall website h What happens if fragment reassembly times