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CSS 432: Routing 1
CSS432 RoutingTextbook Ch4.2
Professor: Munehiro Fukuda
Augmented By Rob Nash
IP on Scale
Addresses are hierarchicalReduces total information storage required to
forward packets Forward packets towards a single network
Then deliver to the host on that network
CSS 432: Routing 2
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.
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Terms
IGPs – Interior Gateway Protocols BGPs – Border Gateway Protocols RIP - Route Information Protocol OSPF – Open Shortest Path First Protocol
ARP – Address Resolution ProtocolMaps IP addrs to physical adapters (MAC addrs)
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ARP
The mechanism that translates from IP GuIDs to underlying physical adapter addressingFrom IP to MAC, for example
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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
Overview
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)
4
3
6
21
9
1
1D
A
FE
B
C
At Node A
E3F
E1E
E2D
E6C
E2B
Next HopCostDestination
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Distance Vector
Each node maintains a set of triples (Destination, Cost, NextHop)
Destination Cost Next hop
B 1 B
C 1 C
D ∞ -
E 1 E
F 1 F
G ∞ -
D
G
A
F
E
B
C
An initial distance vector at node A
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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
Destination Cost Next hop
B 1 B
C 1 C
D 2 C
E 1 E
F 1 F
G 2 F
D
G
A
F
E
B
C
CSS 432: Routing 10
Routing Loop 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…
D
G
A
F
E
B
C
∞
To G in 2
∞
To G in 1
To G in 3
To G in 4
(2) To E in ∞
(1) To E in 2
(3) To E in 3
(5) To E in 4
A
E
B
C(4) To E in ∞
(6) To E in 5
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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)
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)
frame header datagram heaader UDP header RIP Message
Cmd VerAddr family (net addr)
Address of net 1
Routing domain
Route tag
Subnet mask
Next hop address (1-16)Distance to net 1
Addr family (net addr)
Address of net 2
Route tag
Subnet mask
Next hop addressDistance 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
A
C D
X
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|),
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))
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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 17
Graph Theory Visually….
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http://en.wikipedia.org/wiki/Dijkstra's_algorithm
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Dijkstra’s Shortest-Path Algorithm
(A, 0, -)
(A, 0, -) (B, 5, B)(C, 10, C)(E, 2, E)(F, 4, F)
(A, 0, -)(E, 2, E)
(B, 5, B)(C, 10, C)(F, 4, F)
(A, 0, -)(E, 2, E)(F, 4, F)
(C, 10, C)(B, 5, B)
(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)(G, 18, B)
(A, 0, -)(E, 2, E)(B, 5, B)(F, 4, F)(C, 8, B)
(C, 8, B) (G, 15, F)
(A, 0, -)(E, 2, E)(B, 5, B)(F, 4, F)(C, 8, B)(D, 14, C)
(G, 15, F)
(A, 0, -)(E, 2, E)(B, 5, B)(F, 4, F)
(D, 14, C)(G, 15, F)
(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)(C, 8, B)(D, 14, C)
(G, 15, F)
(A, 0, -)(E, 2, E)(B, 5, B)(F, 4, F)(C, 8, B)(D, 14, C)(G, 15, F)
D
G
A
F
E
B
C
11
5
10
3
2
6
4
213
CSS 432: Routing 20
Open Shortest Path First Protocol (OSPF)
Header1. Hello (reachability)2. Database description (topology)3. Link status request4. Link status update5. 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
frame header datagram heaader OSPF header OSPF Message
Version Type(=4)
AreaId
Message Length
Checksum
Authentication 0-3
Authentication type
SourceAddr
Authentication 4-7
# of link status advertisements
Link-state ID
LS Age Options
Advertising router
LS sequence number
Link Checksum Length
0 Flag 0 # of links
Type=1
Link ID
Link data
MetricNum TOSLink type
Optional TOS information
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.
Link State V.S. OSPF
Historically, OSPF has demonstrated more desirable propertiesLess 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
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Practically Speaking…
RIP tells each direct neighbor about everyoneSo, neighbor-to-neighbor dissemination
OSPF (P) tells everyone about my direct neighbors“Reliable” Flooding to all
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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
Internet
Virtual Private Networks and Tunnels
BA
CompanyBranch
CompanyBranch
A B
C
A BApplicationLevel
RouterLevel
PhysicalNetwork Level
Source router Dest router
Router
10.0.0.1 20.0.0.1
10.0.0.1 20.0.0.1
20.0.0.110.0.0.1
To: 20.0.0.1
215.0.0.1
To: 10.0.0.2To: 215.0.0.1 To: 20.0.0.1
To: 20.0.0.1
To: 215.0.0.1
To: 215.0.0.1
To: 215.0.0.1 To: 20.0.0.1
CSS 432: Routing 26
Why VPN?
1. Security The final destination/contents of packet cannot be
easily intercepted. 2. Routers
Routers with special features such as multicasting can form a virtual network.
3. No-IP packets Packets may be non-IP compatible packets.
4. Mobile IPs The final destination may be a mobile computer.
CSS 432: Routing 27
Mobile IP
Homeagent
Internet
Mobile Host10.0.0.9(12.0.0.7)
DHCPserver
Mobile Host
Sending host
10.0.0.3
12.0.0.6
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
CSS 432: Routing 28
Mobile IP (Cont’d)
Homeagent
Internet
Mobile Host10.0.0.9(12.0.0.7)
DHCPserver
Mobile Host
1. ARP request: What’s the physical addr corresponding to 10.0.0.9?
2. ARP response: sends back MAC of10.0.0.3 instead of 10.0.0.9
IP tunneling: wraps the packet inside an IPheader destined for the mobile host (12.0.0.7).
1. DHCP: receives a new IPin the foreign network.
Sending host
3. Packet request: sends a packet destined for 10.0.0.9to the home agent’s MAC address
2. Care-of-address: a mobile host informs itsHome agent of its original and new IPs.
10.0.0.3
12.0.0.6
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)
CSS432: Applications 30
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.
FTP
localfile
system
remotefile
system
FTPserver
FTPclient
FTPuser
interface TCP port 20 for data transfer(not persistent)
TCP port 21 for control (persistent)
CSS432: Applications 31
FTP Commands <CRLF> delimits each command (and reply). Commands consist of four uppercase ASCII characters, some with
optional arguments: USER username : sends a 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 its current 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
FTP
CSS432: Applications 32
FTP ExampleFTP
[mfukuda@uw1-320-20]$ telnet ftp.tripod.com 21Trying 209.202.240.80…Connected to ftp.tripod.com (209.202.240.80).Escape character is ‘^]’.220 Welcome to Tripod FTP.USER css432331 Username set to css432. Now enter your password.PASS ********230 User ‘css432’ logged on.LIST425 Can’t open data connection for LIST.PASV227 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.LIST150 Opening ASCII mode data connection for LIST.226 Transfer complete.QUIT221 GoodbyeConnection closed by foreign host.[mfukuda@uw1-320-20]$ _
CSS432: Applications 33
FTP passive mode
FTPserver
FTPclient
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)
FTPserver
FTPclient
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
FTPServer
2
FTPServer
1
FTPclient
(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
(3’) 227 Entering Passive Mode(140,142,12,173,195,54)
TCP port 195*256 + 54 = 49974 for data transfer (one time)
data
ftp> open server1ftp> proxy open server2ftp> proxy get file
…(1)…(2)…(3)~(5)
Final Project Introduction
FTP project is live on the siteWe’ll worry with the last few steps during
lecture Signing our archives, etc.
CSS 432: Routing 35
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 36
Remote Tips
You can always remote into the lab
You could install Ubuntu on a USB stickHas 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 37
General Tips Observe Dr. Fukuda’s output
It gives away hints left and right
RFC 959 – light reading
Telnet to port 21Act as the client!
For example, what does the server return when you issue a “USER” or “PASV” request?
CSS 432: Routing 38
Telnet Line Terminators
Carridge-Return, Line Feed
Find this out
CSS 432: Routing 39
How Many Lines Of Code?
Decompose the projectA 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 40
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 41
