internet history, architecture, and routing
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Internet History, Architecture, and Routing. ECON 425/563 & CPSC 455/555 9/25/2008. ECON 425/563 & CPSC 455/555 9/25/2008. Internet History. Late 1960s and early 1970s: ARPANET US Department of Defense Connects small ARPA-sponsored data networks - PowerPoint PPT PresentationTRANSCRIPT
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Internet History, Architecture, and Routing
ECON 425/563 & CPSC 455/555
9/25/2008ECON 425/563 & CPSC 455/555
9/25/2008
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Internet History• Late 1960s and early 1970s: ARPANET
– US Department of Defense– Connects small ARPA-sponsored data
networks– Ground breaking testbed for network ideas
and designs• Early 1980s: Other wide-area data networks are
established (e.g., BITNET and Usenet).• Late 1980s and early 1990s:
– “ARPANET” fades out.– US Gov’t sponsors NSFNET, which connects
large regional networks.– Commercial data networks become popular
(e.g., Prodigy, Compuserve, and AOL).
• Mid-1990s: Unified “Internet”
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Internet Protocols Design Philosophy
• Ordered set of goals:1. multiplexed utilization of existing networks2. survivability in the face of failure3. support multiple types of communications
service4. accommodate a variety of network types5. permit distributed management of resources6. cost effective7. low effort to attach a host8. account for resources
• Not all goals have been met
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Packets!• Basic decision: use packets not circuits
(Kleinrock)• Packet (a.k.a. datagram)
– self contained– handled independently of preceding or following
packets– contains destination and source internetwork
address– may contain processing hints (e.g., QoS tag)– no delivery guarantees
– net may drop, duplicate, or deliver out of order– reliability (where needed) done at higher levels
Dest Addr Src Addr payload
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Telephone Network
• Connection-based• Admission control• Intelligence is
“in the network”• Traffic carried by
relatively few, “well-known” communications companies
Internet
• Packet-based• Best effort• Intelligence is
“at the endpoints”
• Traffic carried by many routers, operated by a changing set of “unknown” parties
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Directly Connected Machines
• (a) Point-to-point: e.g., ATM• (b) Multiple-access: e.g., Ethernet• Can’t build a network by requiring all
nodes to be directly connected to each other; need scalability with respect to the number of wires or the number of nodes that can attach to a shared medium
(a)
(b)
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Switched Network
• Circuit switching vs. packet routing• Hosts vs. “the network,” which is made
of routers• Nice property: scalable aggregate
throughput
routers
hosts
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Interconnection of Networks
Recursively build larger networks
gateway
hosts
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Some Hard Questions
• How do hosts share links?• How do you name and address hosts?• Routing: Given a destination address,
how do you get to it?
gateway
hosts
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IP Addresses andHost Names
• Each machine is addressed by an integer, itsIP address, written down in a “dot notation” for “ease” of reading, such as 128.36.229.231
• IP addresses are the universal IDs that are used to name everything.
• For convenience, each host also has ahuman-friendly host name. For example, 128.36.229.231 was concave.cs.yale.edu.
• Question: How do you translate names intoIP addresses?
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Domain Hierarchy
• Initially, name-to-address mappingwas a flat file mailed out to all the machines on the Internet.
• Now, we have a hierarchicalname space, just like a UNIXfile-system tree.
• Top-level names (historical influence): heavily US-centric, government-centric, and military-centric viewof the world
edu com gov mil org net uk fr
Yale MIT Cisco . . . Yahoo
Math CS Physics
concave cyndra netra
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DNS Zones andName Servers
• Divide up the name hierarchy into zones.
• Each zone corresponds to one or more name servers under the same administrative control.
edu com gov mil org net uk fr
Yale MITCisco . . . Yahoo
Math CS Physics
concave cyndra netra
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Hierarchy of Name Servers
• Clients send queries to name servers.• Name servers reply with answers or forward
requests to other name servers.• Most name servers perform “lookup
caching.”
Root name server
Yale name server
CS name server EE name server
Cisco name server. . .
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Application-Level Abstraction
• What you have: hop-to-hop links, multiple routes, packets, can be potentially lost, can be potentially delivered out-of-order
• What you may want: application-to-application (end-to-end) channel, communication stream, reliable, in-order delivery
hostapplication host
host
host
hostapplication
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Basic Architectural Principle: Layering
Internet Protocol
Transmission ControlProtocol
User Datagram Protocol
TelnetHTTP(Web)
SONET ATMEthernet
Simple NetworkManagement
Domain NameService
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Interdomain RoutingEstablish routes between autonomous systems
(ASes).
Currently done with the Border Gateway Protocol (BGP).
AT&T
Qwest
Comcast
Verizon
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Why is Interdomain Routing Hard?
• Route choices are based on local policies.
• Autonomy: Policies are uncoordinated.
• Expressiveness: Policies are complex.
AT&T
Qwest
Comcast
Verizon
My link to UUNET is forbackup purposes only.
Load-balance myoutgoing traffic.
Always chooseshortest paths.
Avoid routes through AT&T ifat all possible.
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BGP Route Processing (1)
• The computation of a single node repeats the following:
Receive routes from neighbors
UpdateRoutin
g Table
Choose“Best”Route
Send updatesto neighbors
• Paths go through neighbors’ choices, which enforces consistency.
• Decisions are made locally, which preserves autonomy.
• Uncoordinated policies can induce protocol oscillations. (Much recent work addresses BGP convergence.)
• Recently, private information, optimization, and incentive-compatibility have also been studied.
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Apply Policy =filter routes & tweak attributes
BGP Route Processing (2)
Routing Table
Apply Import Policies
Best Route Selection
Apply Export Policies
Install forwardingentries for best routes
ReceiveBGPupdates
Storageof routes
TransmitBGP updates
Based onattributevalues
IP Forwarding Table
Apply Policy =filter routes & tweak attributes
Open-ended programming:constrained only by vendor configuration language
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Example: Convergence
1 2
d
Prefer routes
through 2
Prefer direct route
to d
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Example: Oscillation
1 2
d
BGP might oscillateforever between
1d, 2dand
12d, 21d
Prefer routes
through 2
Prefer routes
through 1
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Example: Convergence
1 2
d
Prefer routes
through 2
Prefer routes
through 1
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Dispute Wheels
Nodes ui, hub routes Ri, and spoke routes Qi.Each ui prefers RiQi+1 to Qi.
“No dispute wheel” —>robust convergence
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Gao-Rexford Framework (1)
Neighboring pairs of ASes have one of:– a customer-provider relationship
(One node is purchasing connectivity fromthe other node.)
– a peering relationship(Nodes have offered to carry each other’stransit traffic, often to shortcut a longer route.)
peer
providers
customerspeer
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Gao-Rexford Framework (2)
• Global constraint: no customer-provider cycles• Local preference and scoping constraints, which are
consistent with Internet economics:
• Gao-Rexford conditions => BGP always converges [GR01]
Preference Constraints
. . . . . .
. . . . . .i
dR1
R2
k2
k1
• If k1 and k2 are both customers, peers, or providers of i, then either ik1R1 or ik2R2 can be more valued at i.
• If one is a customer, prefer the route through it. If not, prefer the peer route.
Scoping Constraints
d
k
i
j
• Export customer routes to all neighbors and export all routes to customers.
• Export peer and provider routes to all customers only.
m
. . . .. . . .
. . . .peer
customer
provider
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Ongoing Research Challenge
Fully characterize the conditions under which BGP converges (robustly).
• “No dispute wheel” is sufficient but not necessary. Is it enforceable?
• On those instances on which BGP is guaranteed to converge, how many rounds does it take to converge?