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CSS432 Routing Textbook Ch4.2

CSS432 Routing Textbook Ch4.2. Professor: Munehiro Fukuda Augmented By Rob Nash. IP on Scale. Addresses are hierarchical Reduces total information storage required to forward packets Forward packets towards a single network Then deliver to the host on that network. IP on Heterogeneity.

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CSS432 Routing Textbook Ch4.2

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  1. CSS432 RoutingTextbook Ch4.2 Professor: Munehiro Fukuda Augmented By Rob Nash CSS 432: Routing

  2. IP on Scale • Addresses are hierarchical • Reduces total information storage required to forward packets • Forward packets towards a single network • Then deliver to the host on that network CSS 432: Routing

  3. IP on Heterogeneity • A under-demanding model: “best-effort” • Due to this, IP has been shown to be interoperable with any type of network • Even ones invented after IP • Carrier Pigeons?! • Zebra’s are so much cooler… • http://portal.acm.org/citation.cfm?id=1147620 • Don’t like IP? Aren’t compatible? Try tunneling. CSS 432: Routing

  4. Terms • IGPs – Interior Gateway Protocols • BGPs – Border Gateway Protocols • RIP - Route Information Protocol • OSPF – Open Shortest Path First Protocol • ARP – Address Resolution Protocol • Maps IP addrs to physical adapters (MAC addrs) CSS 432: Routing

  5. ARP • The mechanism that translates from IP GuIDs to underlying physical adapter addressing • From IP to MAC, for example CSS 432: Routing

  6. What Is Routing? • Forwarding vs Routing • forwarding: • To map a network # to an outgoing interface and some MAC information in a forwarding table. • To send a packet to an interface as consulting a local and static forwarding table • OSI Layer 2: data link level • Implemented in specialized hardware (switch) • routing: • To build a dynamic routing table • To update table contents in a dynamic and distributed fashion • OSI Layer 3: network level (internet) • Using complex distributed algorithms CSS 432: Routing

  7. Destination Cost Next Hop B 2 E C 6 E D 2 E E 1 E F 3 E Overview At Node A • Network as a Graph • Goal • Find lowest cost path between two nodes • Static approach has shortcomings: • Hardware failures • Static network topology • Static band width • Distributed, dynamic routing algorithms • Distance vector routing (RIP) • Link state routing (OSPF) CSS 432: Routing

  8. Distance Vector • Each node maintains a set of triples • (Destination, Cost, NextHop) An initial distance vector at node A CSS 432: Routing

  9. Distance Vector • Exchange updates directly connected neighbors • periodically (on the order of several seconds) • whenever table changes (called triggered update) • Each update is a list of pairs: • (Destination, Cost) • From B: (A, 1), (C, 1) • From C: (A, 1), (B, 1), (D, 1) • From E: (A, 1) • From F: (A, 1), (G, 1) • Update local table if receive a “better” route • From B: (C,1) • (C, 1, C) < (C, 2, B) • From C: (D, 1) • (D, ∞, - ) > (D, 2, C) • From F: (G, 1) • (G, ∞, - ) > (G, 2, F) • Refresh existing routes; delete if they are expired CSS 432: Routing

  10. Routing Loop To G in 2 To G in 3 • Failure-recovering scenario • F detects the link to G has failed • F sets distance to G to ∞and sends an update to A • A sets distance to G to ∞ • A receives periodic update from C with a 2-hop path to G • A sets distance to G to 3 and sends update to F • F sets distance to G in 4 hops via A • Count-to-infinity problem • The link from A to E fails • A advertises distance of infinity to E • C advertise a distance of 2 to E • B decides it can reach E in 3 hops • B advertises this to A • A decides it can read E in 4 hops • A advertises this to C • C decides that it can reach E in 5 hops… To G in 1 To G in 4 ∞ B (5) To E in 4 (2) To E in ∞ (3) To E in 3 (4) To E in ∞ (1) To E in 2 A C (6) To E in 5 ∞ E CSS 432: Routing

  11. Loop-Breaking Heuristics • Set infinity to 16 • Scheme: Stop an infinity loop in 16. • Problem: No more 16 hops • Split horizon • Scheme: Don’t send a neighbor the routing information learned from this neighbor. • Ex. B includes (E, 2, A) and thus doesn’t send (E, 3). • Split horizon with poison reverse • Scheme: Send the routing information learned from this neighbor as setting hop count to ∞. • Ex. B includes (E, 2, A) and thus sends (E, ∞, A) • Problem: Its slow convergence speed CSS 432: Routing

  12. Routing Information Protocol (RIP) frame header datagram heaader RIP Message UDP header Ver Routing domain Cmd • Cmd: 1-6 • 1: request • 2: reply • Port: 520 • Used by routed • Advertisement: 30secs • Table entry timeout: 3 mins. • Deleted in 60secs • Unix commands • Ripquery (BSD) • Tcpdump (available in Linux, too) • Snoop (Solaris) Route tag Addr family (net addr) Address of net 1 Subnet mask Next hop address (1-16) Distance to net 1 Route tag Addr family (net addr) Address of net 2 Subnet mask Next hop address Distance to net 2 (1-16) 25 entries CSS 432: Routing

  13. Link State • Strategy • Reliable dissemination of link-state information to all nodes over a system. • Calculation of routes from the sum of all the accumulated link-state knowledge. • Link State Packet (LSP) • ID of the node that created the LSP • A cost of link to each directly connected neighbor • A sequence number (SEQNO) • A time-to-live (TTL) for this packet CSS 432: Routing

  14. Link State (cont) • Reliable flooding • Store most recent LSP from each node • Forward LSP to all nodes but one that sent it • Generate new LSP periodically • Increment SEQNO • Start SEQNO at 0 when reboot • Decrement TTL of each stored LSP • Discard when TTL=0 X A D C B CSS 432: Routing

  15. Dijkstra’s Shortest-Path Algorithm* • put (myself, 0, -) in the confirmed list • Next = myself; • while( true ) { • for each edge (X, distance, Next) where X is N’s neighbor • if neither confirmed or tentative list has (X, distance, Y) where Y != Next, put (X, distance, Next) in the confirmed list • if the tentative list has (X, distance, Y) where Y != Next, and (X, distance, Y) > (X, distance, Next) • Replace (X, distance, Y) with (X, distance, Next) • If the tentative list is empty, • exit • else • move the shortest edge (A, distance, B) from the tentative to the confirmed list. • Next = A • } • //O((|E|+|V|) log |V|) time (which is dominated by O(|E| log |V|), CSS 432: Routing

  16. Forward Search From the Text • M = {me} • For each node n in N - {me} • C(n) = l(me, n) //cost function init • While ( N != M ) • M = M U {w} s.t. C(w) is the min w for all (N-M) • for each n in (N-M) • C(n) = MIN( C(n), C(w) + l(w+n)) CSS 432: Routing

  17. Another OSPF Algorithm • Initialize costs, and start with {me} • While set M is not empty (tentative list) • Pick a node from the tentative list with the lowest cost = m • Move this to the confirmed list • List m’s neigbors, add each to tentative list • If I have a neighbor route already in my tentative list with a higher cost, replace that route CSS 432: Routing

  18. Graph Theory Visually…. http://en.wikipedia.org/wiki/Dijkstra's_algorithm CSS 432: Routing

  19. 3 5 6 10 2 13 4 2 11 Dijkstra’s Shortest-Path Algorithm (D, 14, C) (G, 15, F) (A, 0, -) (E, 2, E) (B, 5, B) (F, 4, F) (C, 8, B) (A, 0, -) (A, 0, -) (B, 5, B) (C, 10, C) (E, 2, E) (F, 4, F) (G, 15, F) (A, 0, -) (E, 2, E) (B, 5, B) (F, 4, F) (C, 8, B) (D, 14, C) (B, 5, B) (C, 10, C) (F, 4, F) (A, 0, -) (E, 2, E) (A, 0, -) (E, 2, E) (F, 4, F) (C, 10, C) (B, 5, B) (G, 15, F) (A, 0, -) (E, 2, E) (B, 5, B) (F, 4, F) (C, 8, B) (D, 14, C) (A, 0, -) (E, 2, E) (F, 4, F) (C, 10, C) (B, 5, B) (G, 15, F) (A, 0, -) (E, 2, E) (B, 5, B) (F, 4, F) (C, 8, B) (D, 14, C) (G, 15, F) (C, 8, B) (G, 18, B) (A, 0, -) (E, 2, E) (B, 5, B) (F, 4, F) (C, 8, B) (G, 15, F) (A, 0, -) (E, 2, E) (B, 5, B) (F, 4, F) (A, 0, -) (E, 2, E) (B, 5, B) (F, 4, F) (C, 8, B) (G, 15, F) CSS 432: Routing

  20. frame header datagram heaader OSPF Message OSPF header # of link status advertisements Type(=4) Message Length Version Options LS Age Type=1 SourceAddr Link-state ID AreaId Advertising router Authentication type Checksum LS sequence number Authentication 0-3 Length Link Checksum Authentication 4-7 0 Flag 0 # of links Link ID Link data Metric Link type Num TOS Optional TOS information Open Shortest Path First Protocol (OSPF) • Header • Hello (reachability) • Database description (topology) • Link status request • Link status update • Link status acknowledgment • Advertisement (header type=4) • LS Age: = TTL • Type=1: link cost b/w routers • Link-State ID = Advertising Router • Seq # from the same router • Link ID = the other end route ID of link • Link data = used if there are two or more links to the same router • Metric = link cost • Link type = P2P, ethernet, etc • TOS = delay-sensitive, etc CSS 432: Routing

  21. OSPF Con’td • Gated daemon: directly uses IP datagram. • Header Type2: Database description (topology) message • Used when the current topology has changed. • Sent from an initialized router to another router which has a topology information • LS Sequence number • Used to determine which message is the latest • Send a message with a new sequence number and metric= ∞ when a router or a link fails. CSS 432: Routing

  22. Link State V.S. OSPF • Historically, OSPF has demonstrated more desirable properties • Less bandwidth usage on large networks • After init, OSPF LPSs are deltas • Convergence speed • Rip can take 10, 30, even 60 seconds • OSPF supports CIDR & netmasks CSS 432: Routing

  23. Practically Speaking… • RIP tells each direct neighbor about everyone • So, neighbor-to-neighbor dissemination • OSPF (P) tells everyone about my direct neighbors • “Reliable” Flooding to all CSS 432: Routing

  24. Metrics • Original ARPANET metric • measures number of packets enqueued on each link • took neither latency or bandwidth into consideration • New ARPANET metric • stamp each incoming packet with its arrival time (AT) • record departure time (DT) • when link-level ACK arrives, compute Delay = (DT - AT) + Transmit + Latency • if timeout, reset DT to departure time for retransmission • link cost = average delay over some time period • Fine Tuning • compressed dynamic range • replaced Delay with link utilization CSS 432: Routing

  25. To: 20.0.0.1 To: 215.0.0.1 To: 215.0.0.1 To: 215.0.0.1 Virtual Private Networks and Tunnels 10.0.0.1 20.0.0.1 A Application Level B Router Dest router Source router 10.0.0.1 20.0.0.1 Router Level B A To: 20.0.0.1 To: 215.0.0.1 To: 20.0.0.1 To: 10.0.0.2 Internet C 215.0.0.1 Company Branch Company Branch Physical Network Level To: 20.0.0.1 A B 20.0.0.1 10.0.0.1 CSS 432: Routing

  26. Why VPN? • Security • The final destination/contents of packet cannot be easily intercepted. • Routers • Routers with special features such as multicasting can form a virtual network. • No-IP packets • Packets may be non-IP compatible packets. • Mobile IPs • The final destination may be a mobile computer. CSS 432: Routing

  27. Sending host Mobile Host 10.0.0.9 (12.0.0.7) Mobile Host Mobile IP • Invariant: Sending hosts want to use the same IP address mapped to a mobile host regardless of its location. • Questions • How does the home agent intercept a packet that is destined for the mobile agent? --- Use ARP • How does the home agent then deliver the packet to the mobile host? – Use DHCP and VPN 10.0.0.3 Internet DHCP server Home agent 12.0.0.6 CSS 432: Routing

  28. Sending host Mobile Host 10.0.0.9 (12.0.0.7) Mobile Host Mobile IP (Cont’d) 1. ARP request: What’s the physical addr corresponding to 10.0.0.9? 3. Packet request: sends a packet destined for 10.0.0.9 to the home agent’s MAC address 2. ARP response: sends back MAC of 10.0.0.3 instead of 10.0.0.9 1. DHCP: receives a new IP in the foreign network. 10.0.0.3 Internet DHCP server Home agent 12.0.0.6 IP tunneling: wraps the packet inside an IP header destined for the mobile host (12.0.0.7). 2. Care-of-address: a mobile host informs its Home agent of its original and new IPs. CSS 432: Routing

  29. Reviews • RIP: distance vector, routing loop and breaking heurictics • OSPF: link state, Dijkstra’s shortest path algorithm • VPN and mobile IP • Exercises in Chapter 4 • Ex. 15 (RIP) • Ex. 18 (RIP) • Ex. 28 (OSPF) • Ex. 30 (OSPF) CSS 432: Routing

  30. FTP user interface FTP client FTP server TCP port 21 for control (persistent) TCP port 20 for data transfer (not persistent) local file system remote file system FTP File Transfer Protocol • Transfer file to/from remote host • Client/server model • Client:initiates a control TCP connection to a server on port 21. • Client:sends a user ID and password as part of FTP commands. • Server:authorizes the client • Client:opens a data TCP connection to a server on port 20. • Server:maintains state: current directory, earlier authentication. • A ftp client is allowed to initiate a transfer between two ftp servers. CSS432: Applications

  31. FTP FTP Commands • <CRLF>delimits each command (and reply). • Commands consist of four uppercase ASCII characters, some with optional arguments: • USER username : sendsa user identification to server. • PASS password : sends the user password to the server. • PASV: requests the server to send back its IP and port on which it listens to a data TCP connection from the user. • LIST :ask the server to send back itscurrent directory contents through the data connection. • RETR filename : gets a file from the current remote directory. • STOR filename : stores a file into the current remote directory. • Each command is followed by a reply: • 331 Username OK, password required • 125 Data connection already open; transfer starting • 425 Can't open data connection • 452 Error writing file CSS432: Applications

  32. FTP FTP Example [mfukuda@uw1-320-20]$ telnet ftp.tripod.com 21 Trying 209.202.240.80… Connected to ftp.tripod.com (209.202.240.80). Escape character is ‘^]’. 220 Welcome to Tripod FTP. USER css432 331 Username set to css432. Now enter your password. PASS ******** 230 User ‘css432’ logged on. LIST 425 Can’t open data connection for LIST. PASV 227 Entering Passiv Mode (209,202,240,80,195,210) // Open another xterm and telnet 209.202.240.80 50130 (=195*256+210) // Trying 209.202.240.80… // Connected to ftp.tripod.com (209.202.240.80). // Escape character is ‘^]’. // drwxr-xr-x 1 css432 Tripod 0 Sep 15 21:22 cgi-bin // -rw-r--r-- 1 css432 Tripod 26169 Sep 16 18:28 ttcp.c // -rw-r--r-- 1 css432 Tripod 8236 Sep 15 21:22 index.htm // drwxr-xr-x 1 css432 Tripod 0 Sep 16 18:33 project // Connection closed by foreign host. LIST 150 Opening ASCII mode data connection for LIST. 226 Transfer complete. QUIT 221 Goodbye Connection closed by foreign host. [mfukuda@uw1-320-20]$ _ CSS432: Applications

  33. FTP passive mode FTP client FTP server TCP port 21 for control (persistent) Client request: connect( ), USER, PASS, LIST Server Reply: 220 server ready, 331 send password, 230 login ok, 425 connection timeout TCP port 20 for data transfer (one time) FTP client FTP server TCP port 21 for control (persistent) Client request: connect( ), USER, PASS, PASV, LIST Server Reply: 220 server ready, 331 send password, 230 login ok, 227 Entering Passive Mode (140,142,12,173,195,54), 226 complete TCP port 195*256 + 54 = 49974 for data transfer (one time) data CSS432: Applications

  34. FTP proxy command (3’) 227 Entering Passive Mode (140,142,12,173,195,54) FTP client (1) USER, PASS, SYST (2) USER, PASS, SYST (3) TYPE I, PASV (4) TYPE I, PORT (140,142,12,173,195,54), STOR file (5) RETR file ftp> open server1 ftp> proxy open server2 ftp> proxy get file …(1) …(2) …(3)~(5) FTP Server 1 FTP Server 2 TCP port 195*256 + 54 = 49974 for data transfer (one time) data CSS432: Applications

  35. Final Project Introduction • FTP project is live on the site • We’ll worry with the last few steps during lecture • Signing our archives, etc. CSS 432: Routing

  36. FTP is Fun Transfer Protocol! (If you tend to think bytes are fun) We’re making a client to interface with an existing server (a class of servers) CSS 432: Routing

  37. Remote Tips • You can always remote into the lab • You could install Ubuntu on a USB stick • Has a good ftp server to play with • https://help.ubuntu.com/6.06/ubuntu/serverguide/C/ftp-server.html • You write the client to interact with this server CSS 432: Routing

  38. General Tips • Observe Dr. Fukuda’s output • It gives away hints left and right • RFC 959 – light reading • Telnet to port 21 • Act as the client! • For example, what does the server return when you issue a “USER” or “PASV” request? CSS 432: Routing

  39. Telnet Line Terminators Carridge-Return, Line Feed Find this out CSS 432: Routing

  40. How Many Lines Of Code? • Decompose the project • A network component • Resue code here from previous projects • A filesystem component • Reuse code here if you have it! • From Pseudocode to C, or • Pseudocode->intermediary language -> C CSS 432: Routing

  41. Overarching Strategy • (0) Introduce yourself to the server • (1) Relay a request to the server • (2) Get a socket for data transmission • See PASV • (3) Exchange data in ASCII or Binary • (4) Loop to (1) or QUIT CSS 432: Routing

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