Announcements Additional office hours Sukun next week Friday 1 3PM Dilip likely next Weds Thurs along with regular Fri Me next week regular Weds by appointment Final Review Course evaluations today 5 20PM No 5 minute break during this lecture EE 122 Intro to Communication Networks Fall 2006 MW 4 5 30 in Donner 155 Vern Paxson TAs Dilip Antony Joseph and Sukun Kim http inst eecs berkeley edu ee122 Materials with thanks to Jennifer Rexford Ion Stoica and colleagues at Princeton and UC Berkeley 1 2 Final Review Fundamental Challenges for Networking Saturday Dec 16 8AM 11AM in 2 Le Conte Speed of light Near Evans Bancroft Library Desiring a pervasive global network Closed book You can have one regular sized 8 5 x11 sheet of paper with notes on both sides Need for it to work efficiently cheaply Failure of components No PDAs calculators electronic Internet gadgets smart cell phones jeweler s loupes etc Enormous dynamic range No Blue Books all answers on exam sheets Disparate parties must work together Ensure legibility pencil eraser Rapid growth evolution no such thing as typical Crooks other bad guys Emphasis is on material since midterm 3 Avoiding Manual Configuration Key Ideas in Both Protocols Dynamic Host Configuration Protocol DHCP Broadcasting when in doubt shout End host learns how to send packets Learn IP address DNS servers gateway what s local Caching remember the past for a while Soft state eventually forget the past Address Resolution Protocol ARP Key for robustness in the face of unpredictable change For local destinations learn mapping between IP address and MAC address 1 2 3 48 1 2 3 7 1 2 3 156 host host 1 2 3 0 23 255 255 254 0 DNS 1A 2F BB 76 09 AD host 4 host DNS 5 6 7 0 24 1 2 3 19 router router router 5 6 1 Figuring Out Where To Send Locally Dynamic Host Configuration Protocol Two cases Destination is on the local network DHC P dis cove r broa dcas t So need to address it directly Destination is not local remote Need to figure out the first hop on the local network Determining if it s local use the netmask arriving client er P off DHC E g mask destination IP address w 255 255 254 0 Is it the same value as when we mask our own address DHCP server 203 1 2 5 Yes local No remote DHC P req uest broa dcas t 1 2 3 48 1 2 3 7 1 2 3 156 host K P AC DHC host DNS 1 2 3 19 router 7 host host 5 6 7 0 24 1 2 3 0 23 255 255 254 0 Address Resolution Protocol DNS 1A 2F BB 76 09 AD router router 8 Example A Sending a Packet to B Every node maintains an ARP table How does host A send an IP packet to host B IP address MAC address pair Consult the table when sending a packet A But what if IP address not in the table Sender broadcasts Who has IP address 1 2 3 156 Receiver responds MAC address 58 23 D7 FA 20 B0 Sender caches result in its ARP table R Link layer protocol RFC826 B Not IP or UDP or TCP over IP because IP requires that you already know the destination IP address 9 Security Analysis of ARP Impersonation Any node that hears request can answer and can say whatever they want Actual legit receiver never sees a problem Because even though later packets carry its IP address its NIC doesn t capture them since not its MAC address Or Man in the middle attack Imposter forwards everything it receives for destination but gets to inspect maybe alter it first Does the attacker have to win a race Maybe not if sender blindly believes ARP responses Different attack overflow ARP table force evictions 11 10 Internet Control Message Protocol ICMP runs on top of IP Viewed as an integral part of IP Not viewed as a transport protocol Diagnostics Triggered when an IP packet encounters a problem E g Time Exceeded or Destination Unreachable ICMP packet sent back to the source IP address Includes the error information e g type and code and IP header plus 8 byte excerpt from original packet Source host receives the ICMP packet Inspects excerpt e g protocol and ports to identify which socket should receive the error 12 2 Path MTU Discovery MTU Maximum Transmission Unit Largest IP packet that a link supports Path MTU PMTU minimum end to end MTU Sender must keep datagrams no larger to avoid fragmentation How does the sender know the PMTU is Strategy RFC 1191 Try a desired value Set DF to prevent fragmentation Upon receiving Need Fragmentation ICMP oops that didn t work try a smaller value 13 Link State Routing Dijsktra s Algorithm Each router has a complete picture of the network C A Host A B Host CA D E A Host B C B A C A C D D Host D B B N2 N1 E E C D N3 D N5 E B A E C A D B N4 N6 traceroute to www whitehouse gov 204 102 114 49 30 hops max 40 byte packets 1 cory115 1 gw EECS Berkeley EDU 128 32 48 1 0 829 ms 0 660 ms 0 565 ms 2 cory cr 1 1 soda cr 1 2 EECS Berkeley EDU 169 229 59 233 0 953 ms 0 857 ms 0 727 ms 3 soda cr 1 1 soda br 6 2 EECS Berkeley EDU 169 229 59 225 1 461 ms 1 260 ms 1 137 ms 4 g3 8 inr 202 reccev Berkeley EDU 128 32 255 169 1 402 ms 1 298 ms Lost Reply 5 ge 1 3 0 inr 002 reccev Berkeley EDU 128 32 0 38 1 428 ms 1 889 ms 1 378 ms 6 oak dc2 ucb ge cenic net 137 164 23 29 1 731 ms 1 643 ms 1 680 ms 7 dc oak dc1 oak dc2 p2p 2 cenic net 137 164 22 194 3 045 ms 1 640 ms 1 630 ms 8 Router doesn t send ICMPs 9 dc lax dc1 sac dc1 pos cenic net 137 164 22 126 13 104 ms 13 163 ms 12 988 ms No PTR record for address 10 137 164 22 21 137 164 22 21 Final Hop 13 328 ms 42 981 ms 13 548 ms 11 dc tus dc1 lax dc2 pos cenic net 137 164 22 43 18 775 ms 17 469 ms 21 652 ms 12 a204 102 114 49 deploy akamaitechnologies com 204 102 114 49 18 137 ms 14 905 ms 19 730 ms 14 B E C D HostE E N7 How does each router get the global state Each router reliably floods information about its neighbors to every other router more later Each router independently calculates the shortest path from itself to every other router Dijkstra s Shortest Path Algorithm 1 Initialization 2 S A 3 for all nodes v …
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