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EE4L Computer _ Communication Networks Powered By Docstoc
					          EE4L
Computer & Communication
        Networks
    Part III – Internet routing
       Dr Costas Constantinou
         Internet Exterior Routing
1.   Internet Topology
2.   Path Vector Protocols
3.   BGP
4.   Policy Routing
5.   Convergence, Stability & Open Problems

Acknowledgements:
    Slides adapted from numerous sources. Thanks go (alphabetically) to, Dr
     Lawrie Brown, University of New South Wales; Prof. Chen-Nee Chuah,
     University of California, Davis; Prof. Michalis Faloutsos, University of
     California, Riverside; Dr Tim Griffin, University of Cambridge; Prof.
     Jennifer Rexford, Princeton University; & Prof. Ion Stoica, University of
     California, Berkeley
         1. Internet Topology
• Internet – network of networks
  – Each network is an Autonomous System (AS)
    comprising many subnets connected by routers under
    a single administrative control
  – Routing in each network is done by an interior gateway
    routing protocol (IGP) such as IS-IS, OSPF (both are
    link-state) or RIP (distance vector)
• Characterised by constant change & rapid growth
  – Requires adaptive protocols
  – No central authority requires we employ distributed
    adaptive protocols
  – Need to use of compact addressing schemes and
    router table entries to ensure scalability
          1. Internet Topology
How big is the Internet? In July 2009 there were an estimated
681,064,561 hosts (publicly visible networked computers)
          1. Internet Topology
How big is the Internet? On 07-Jan-2010 07:55 UTC there were
61,438 ASs assigned to ISPs worldwide by IANA




                             Source: Geoff Huston, http://bgp.potaroo.net
           1. Internet Topology
Not all networks are willing to tell you they are out there!




                                Source: Geoff Huston, http://bgp.potaroo.net
            1. Internet Topology
Active BGPv4 Routing Information Base (RIB) [Router Table] entries




                               Source: Geoff Huston, http://bgp.potaroo.net
         1. Internet Topology
BGP Routing Updates 31-December-2009 – 6-January-2010




                              Source: Geoff Huston, http://bgp.potaroo.net
          1. Internet Topology
BGP average path length (in hops) on Jan 7 10:30:01 2010 GMT




                       Source: http://www.cymru.com/BGP/avg_aspath_len.html
         2. Basic Graph Theory
                                                                3
                                                       2    2       3
• Networks as graphs
                                         1   2    3
• What is a graph?
                                           1
• G=(N,V) is a finite nonempty set N of       4
                                                1
                                                                    5

  nodes/vertices and a set V of links/arcs/edges
  (i.e. a pair of distinct nodes from N)
   – e.g. N = {1, 2, 3, 4, 5}, V = {(1,2), (2,3), (1,4), (2,4), (4,3),
     (4,5)}
   – A walk is a sequence of nodes (1, 2, …m) such that
     each of the pairs (1, 2) , (2, 3),… (m–1, m) are arcs of G
   – A path is a walk with no repeated nodes
   – Edges may have weights associated with them
            2. Basic Graph Theory
    – A cycle is a walk (1, 2, …m) with 1 = m, m > 3, and no
      repeated nodes other than the start and end node
    – A graph is connected if for each node i there is a path
      to each other node j
    – G = (N,V) is a subgraph of G = (N,V) if N  N and
      V  V

             3                                               3
    2   2            3       2   2           3       2   2           3

1       2        3       1       2               1               3
    1                        1                       1
        4            5           4                       4
            1
(a) connected            (b) not connected       (c) subgraph of (a)
     2. Basic Graph Theory
– A tree is a connected graph that contains no cycles
– A spanning tree of a graph G is a subgraph of G that
  is a tree and includes all the nodes of G
– How to construct a spanning tree of an arbitrary
  graph G?
      1. Let m be an arbitrary node in N. Let N' = {m}, and
         V' = {}
      2. If N' = N, then stop. G' = (N',V') is a spanning tree. Else
         go to step 3.
      3. Let (i, j)  V be an arc with i  N', j  N – N'
         Update N' and V' by N' := N'  {j} and V' := V'  {(i, j)}
         Go to Step 2
             2         3                     2        3

      1                             1

             4         5                     4        5
          2. Basic Graph Theory
•   Properties of Graph
    –    Proposition
        • Let G be a connected graph with N nodes and V
           arcs
        • Then:
           1. G contains a spanning tree
           2. V ≥ N − 1
           3. G is a tree if and only if V = N − 1
        2. Basic Graph Theory
• A Spanning Tree (ST) is an acyclic subgraph
  (part of the original graph with no closed loop),
  and it connects all nodes in the network
   – Can construct a ST rooted at some node, say node 1,
     and send packets from the node to all its neighbours;
     and neighbours must send packets to their
     neighbours, and so on …
   – But such a ST has no special properties
   – Must take cost/delay of a link into consideration
                          2      3

                   1

                          4      5
        2. Basic Graph Theory
• Shortest Path Tree (SPT)
  – ST rooted at a source node, with shortest paths from
    a source node s to any other node d in the network


                3
        2   2           3                    2     2        3

    1       2               1   SPT(1)   1
                 2                                      2
        1                                    1
            4           5                          4        5
                1                                      1
        Given graph G                            SPT of G
        2. Basic Graph Theory
• Minimum Weight Spanning Tree (MWST)
  – A ST with the least total weight of the links in the ST
    among all possible STs

                3
        2   2           3                  2     2         3

    1       2               1   MWST   1                   1
                 2
        1                                  1
            4           5                        4         5
                1                                    1
        Given graph G                          MWST of G
    2. Routing as a Graph Theory
               Problem
• Routing protocol                            4
  problem definition:                             3
                                          2   2       3   5
  – Determine “best” path
    from source to destination        1       2
                                                  3   2       6
    optimising some criteria              1               1
                                              4       5
  – Graph abstraction for                         1
    routing algorithms:
     • Graph nodes are routers        – Optimal path typically
     • Graph edges are physical         means minimum cost
       links                            path (other definitions
     • Link cost: delay, £ cost, or
       congestion level                 possible)
 2. Routing Algorithm Classification
• Global or decentralised          • Static or dynamic?
  information?                     • Static:
• Global:                             – Routes change slowly over
   – All routers have complete          time
     topology, link cost           • Dynamic:
     information
                                      – Routes change more
   – Link state algorithms              quickly
• Decentralised:                      – Periodic update in
   – Router knows physically            response to link cost
     connected neighbours, link         changes, new or defunct
     costs to neighbours                links
   – Iterative process of
     computation, exchange of
     information with neighbours
   – Distance vector algorithms
2. You Should Already Know These
• Routing techniques
  – Flooding
  – Dijkstra (Link State Protocol)
  – Bellman Ford (Distance Vector)
• What is their computational complexity?
• How do they compare in performance?
  – Convergence time
  – Communication overhead
  – Computation overhead
• IP Addressing
  – Classless Interdomain Routing (CIDR), longest prefix
    matching in routing tables
      2. Path Vector Protocols
• Link-State Routing is Problematic
  – Topology information is flooded
     • High bandwidth and storage overhead
     • Forces nodes to divulge sensitive information
  – Entire path computed locally per node
     • High processing overhead in a large network
  – Minimizes some notion of total distance
     • Works only if policy is shared and uniform
  – Typically used only inside an AS
     • E.g., OSPF and IS-IS
      2. Path Vector Protocols
• Distance Vector is on the right track
  – Advantages
     • Hides details of the network topology
     • Nodes determine only “next hop” toward the destination
  – Disadvantages
     • Minimises some notion of total distance, which is difficult in
       an inter-domain setting
     • Slow convergence due to the counting-to-infinity problem
       (“bad news travels slowly”)
  – Idea: extend the notion of a distance vector
     • To make it easier to detect loops
        2. Path Vector Routing
• Extension of distance-vector routing (still uses [a
  slightly modified] Bellman-Ford algorithm)
   – Support flexible routing policies
   – Avoid count-to-infinity problem
• Key idea: advertise the entire path
   – Distance vector: send distance metric per destination d
   – Path vector: send the entire path for each destination d

                    “d: path (2,1)”         “d: path (1)”
       3                              2                     1
                    data traffic            data traffic
                                                            d
       2. Path Vector Routing
• Dispense with routing metrics
• Provide information about:
  – Which networks can be reached by given router
  – Which ASs must be crossed to get there
• No distance or cost element
• Routing information includes all ASs visited to
  reach destination
  – Allows policy routing
      2. Faster Loop Detection
• Nodes can easily detect a loop
  – Look for its own node identifier in the path
  – E.g., node 1 sees itself in the path “3, 2, 1”
• Node can simply discard paths with loops
  – E.g., node 1 simply discards the advertisement


                    “d: path (2,1)”             “d: path (1)”
       3                                 2                      1


                            “d: path (3,2,1)”
          2. Path Vector Protocols
                                                                                       (3,6)
                                                                                      (3,5,6)
          2                   3           (6)       (2,3,6)             2                       3               (3,5,6)




                                                                            (2,3,6)
                                                              (4,3,6)
1                                               6   1         (4,5,6)                 (3,6)                         6
                                                                                     (3,5,6)
                                                                                 (4,3,6)                        (5,3,6)
          4                   5           (6)                           4                       5
                                                                                   (5,6)
    (a)                                                 (c)
                                                                                  (5,3,6)

                (3,6)
          2                   3                                         2                       3




                                                                                                    (5,4,3,6)
              (3,6)
1                                 (3,6)         6   1                                                               6
                      (5,6)

          4                   5                                         4                       5
                (5,6)
    (b)                                                 (d)                  etc., etc.
2. Path Vector Protocols + Policies
•   Hear advertisements: IP prefix, AS-path
•   Policies I: Filter if desired (i.e. ignore)
•   Append yourself: IP prefix, myAS+AS-path
•   Policies II: Forward to appropriate ASs
           2. Flexible Policies
• Each node can apply local policies
  – Path selection: Which path to use?
  – Path export: Which paths to advertise?
• Examples
  – Node 2 may prefer the path (2, 3, 1) over (2, 1)
  – Node 1 may not let node 2 hear the path (1, 3)

    2               3             2
                                                  3


                                        
            1                               1
      3. Border Gateway Routing
           Protocol (BGP-4)
• De-facto inter-domain routing protocol for Internet
  – Prefix-based path-vector protocol
  – Policy-based routing based on AS Paths
  – Evolved during the past 21 years:
     •   1989 : BGP-1 [RFC 1105], replacement for EGP
     •   1990 : BGP-2 [RFC 1163]
     •   1991 : BGP-3 [RFC 1267]
     •   1995 : BGP-4 [RFC 1771], support for CIDR
     •   2006 : BGP-4 [RFC 4271], update
  – BGP includes specifications on which information gets
    advertised and how
• BGP includes a routing protocol:
  – Establishes and uses a routing table
  – External & Internal Gateway Protocols (eBGP & iBGP)
 3. Why Is There Such Fuss about
              BGP?
• BGP dictates routing at the AS level
  – Absence of understanding: poor performance
• BGP is complicated
  – Designed to be flexible
  – Involves multiple fields
• Understanding BGP behaviour is not intuitive
  – Implementation and business policies
• The cohesive operation of the Internet relies on
  BGP
3. BGP Operations (Simplified)
  Establish session on
                          AS1
     TCP port 179


                                        BGP session
     Exchange all
     active routes
                                                 AS2

                         While connection
 Exchange incremental    is ALIVE exchange
      updates            route UPDATE messages
   3. Border Gateway Protocol
• Allows routers (gateways) in different ASs to
  exchange routing information
• Messages sent over TCP port 179
  – See next slide
• Three functional procedures
  – Neighbour acquisition
  – Neighbour reachability
  – Network reachability
          3. BGP v4 Messages
• Open
   – Start neighbour relationship with another router
• Update
   – Transmit information about single route
   – List multiple routes to be withdrawn
• Keepalive
   – Acknowledge open message
   – Periodically confirm neighbour relationship
• Notification
   – Send when error condition detected
  3. BGP Neighbour Acquisition
• Neighbours attach to same subnetwork
• If in different ASs routers may wish to exchange
  information
• Neighbour acquisition occurs when two
  neighbouring routers agree to exchange routing
  information regularly
  – Needed because one router may not wish to take part
• One router sends a request, the other
  acknowledges
  – Knowledge of existence of other routers and need to
    exchange information established at configuration
    time or by active intervention
             3. BGP Reachability
•   Neighbour reachability:
    –   Periodic issue of keepalive messages
    –   Between all routers that are neighbours
•   Network Reachability
    –   All BGP routers build up and maintain routing
        information
    –   Incremental protocol
        •  Each router learns multiple paths to each destination and
           keeps a database of subnetworks it can reach:
        1. Stores all of the routes in a routing table
        2. Applies policy to select a single active (preferred) route
        3. … and may advertise the route to its neighbours
        3. BGP Reachability (cont.)
•   Network Reachability (cont.)
    –    Incremental updates
         •    Announcement
         1.   Upon selecting a new active route, add node id to path
         2.   … and (optionally) advertise to each neighbour
         •    Withdrawal
         1.   If the active route is no longer available send a withdrawal
              message to the neighbors
    –    When a change occurs, router issues update
         messages unlike, say, RIP which does this
         periodically, as it uses unreliable UDP rather than
         reliable TCP message exchanges
    3. BGP Message Formats
• Marker:
  – Reserved for
    authentication
• Length:
  – In octets
• Type:
  – Open, Update,
    Keepalive, Notification
 3. Neighbour Acquisition Detail
• Router opens TCP connection with neighbor
• Sends open message
  – Identifies sender’s AS and gives IP address
  – Includes Hold Time
     • As proposed by sender
• If recipient prepared to open neighbour
  relationship
  – Calculates hold time (typically  180 s)
     • min [own hold time, received hold time]
     • Max time between keepalive/update messages
  – Replies with keepalive
               3. Other Details
• Keepalive Detail
  – Header only
  – Often enough to prevent hold time expiring ( 60 s)
• Update Detail
  – Information about single route through Internet
     • Information to be added to database of any recipient router
     • Network layer reachability information (NLRI): List of network
       portions of IP addresses of subnets reached by this route
     • Total path attributes length field
     • Path attributes field (next slide)
  – List of previously advertised routes being withdrawn
  – May contain both
• Withdrawal of Route
  – Route identified by IP address of destination subnet
       3. Path Attributes Field
• Origin
  – Interior (e.g. OSPF) or exterior (BGP) protocol
• AS_Path
  – ASs traversed for this route
• Next_Hop
  – IP address of border router for next hop
• Multi_Exit_disc
  – Information about routers internal to AS
• Local_Pref
  – Tell other routers within AS degree of preference
• Atomic_Aggregate, Aggregator
  – Uses subnet addresses in tree view of network to
    reduce information needed in NLRI
       3. Notification Message
• Error notification
• Message header error
  – Includes authentication and syntax errors
• Open message error
  – Syntax errors and option not recognised
  – Proposed hold time unacceptable
• Update message error
  – Syntax and validity errors
• Hold time expired
• Finite state machine error
• Cease
  – Close connection in absence of any other error
           3. BGP Route Processing
                       Open ended programming.
             Constrained only by vendor configuration language


Receive Apply Policy =     Based on      Best Routes Apply Policy =        Transmit
BGP     filter routes &    Attribute     (not shortest) filter routes &    BGP
Updates tweak attributes   Values                       tweak attributes   Updates

         Apply Import      Best Route     Best Route       Apply Export
          Policies          Selection      Table            Policies



                                                Install forwarding
                                                Entries for best
                                                Routes.


                                        IP Forwarding Table
                                                                               42
 4. BGP Policy: Applying Policy to
             Routes
• Import policy
  – Filter unwanted routes from neighbour
     • E.g. prefix that your customer doesn’t own
  – Manipulate attributes to influence path selection
     • E.g., assign local preference to favoured routes
• Export policy
  – Filter routes you don’t want to tell your neighbour
  – Manipulate attributes to control what they see
     • E.g., make a path look artificially longer than it is
3. Diagram for BGP Routing
   Information Exchange
       3. BGP Routing Information
               Exchange
• R1 constructs routing table for AS1 using OSPF/IS-
  IS/RIP
• R1 issues update message to R5 (in AS2)
   – AS_Path: identity of AS1
   – Next_Hop: IP address of R1
   – NLRI: List of all subnets in AS1
• Suppose R5 has neighbour relationship with R9 in AS3
• R5 forwards information from R1 to R9 in update
  message
   – AS_Path: list of ids {AS2,AS1}
   – Next_Hop: IP address of R5
   – NLRI: All subnets in AS1
• R9 decides if this is preferred route and forwards to
  neighbours
3. Routing Domain Confederations
• Set of connected ASs
• Appear to the outside world as a single AS
  – This may be recursive
• Effective scaling of routing tables over and
  above CIDR
    4. Meanwhile, back in the real
             world ...
• Thousands of ASs
• Complicated relationships
  – Not all ASs are equal
• Multiple providers for one AS
  – Multihoming
• Traffic engineering
  – I want to use multiple paths and load balance
      4. Basic AS relationships
• Customer – Provider
   – Customer pays Provider for service
   – The Customer is always right
• Peer to Peer: mutual cooperation (i.e. exchange
  traffic only between their customers)
   – E.g. MCI and AT&T
• Sibling-Sibling (i.e. exchange all traffic
  indiscriminately)
   – E.g. AT&T research and AT&T wireless
      4. Customers and Providers

                                  provider




provider           customer                                    IP traffic


                                  customer



           Customer pays provider for access to the Internet
      4. The “Peering” Relationship




   peer    peer           Peers provide transit between
provider   customer       their respective customers

                          Peers do not provide transit
                          between peers
traffic     traffic NOT
allowed     allowed       Peers (often) do not exchange $$$
    4. Peering Provides Shortcuts




Peering also allows connectivity between      peer    peer

the customers of “Tier 1” providers.       provider   customer
   4. Peering – The Initial Idea
• Data flows between customers-providers
• Top level providers are peers
  – They exchange information to ensure connectivity
• What can possibly go wrong?
             4. Peering “Wars”
         Peer                       Don’t Peer
• Reduces upstream transit    • You would rather have
  costs                         customers
• Can increase end-to-end     • Peers are usually your
  performance                   competition
• May be the only way to
  connect your customers to   • Peering relationships may
  some part of the Internet     require periodic
  (“Tier 1”)                    renegotiation


Peering struggles are by far the most contentious issues
in the ISP world

Peering agreements are often confidential
4. The Intended Use of Peering




                Provider    Customer
                   Peer      Peer
                Data flow
       4. BGP Graphs & Associated
            Routing Policies
          100                 200


  10              11          12              13




  1               2           3                4

• Up then down: 1, 10, 100, 200, 12, 3
• No valleys, no up-down-up, no more than 1
  peer-peer hop
 4. The “Rules” of BGP Routing
• Transit traffic: traffic that does not go to my
  customers (or their customers) – note different
  definition from conventional one!
• A provider carries any traffic to & from customer
• Peers exchange traffic only if this goes between
  their customers
   4. Implementing BGP Rules
• Customers advertise whatever they want
• Providers forward everything from (paying)
  customer
  – So that the rest of the world knows where the
    customer IP addresses can be found
• A provider advertises whatever customer they
  want to its customers
• A peer hears but does not advertise further IP
  address prefixes from a peer
• A peer advertises only its own customers to a
  peer
      4. Some Simple Policies:
            Transitivity
             ISP 1          ISP 2



                                    Not allowed
                           AS X

• A customer can never transit routes for its
  providers
  – AS X should not advertise ISP 1 advertisements
4. How Policies Affect Routing
  Customer 1       • A Provider will get rid
                     of traffic as soon as
                     possible (“hot potato
       ISP1          routing”),
                   • But a Provider will
                     carry the traffic for its
                     customer
      ISP2
                   • Traffic paths are
                     asymmetric most of
                     the time

      Customer 2
4. BGP Path-Length Asymmetry




• Consider number of AS traversed by a path
• Asymmetry: 46% of pairs differ by at least one AS hop
                                           [Siganos, 2001]
    4. AS is Not a Single Node
• AS path length can be misleading
  – An AS may have many router-level hops

           BGP says that path 4 1
           is better than path 3 2 1


                                       AS 4
         AS 3

            AS 2


                   AS 1
 4. An AS is Not a Single Node
• Multiple routers in an AS
  – Need to distribute BGP information within the AS
  – Internal BGP (iBGP) sessions between routers

    AS1
                eBGP


                             iBGP

                                        AS2
 4. An AS is Not a Single Node
• Multiple connections to neighboring ASs
  – Multiple border routers may learn good routes with
    the same local-pref and AS path length
              Multiple links

                                   4
          3

                                                5

      2
                               7                     6

  1
 4. Hot-Potato (Early-Exit) Routing
• Hot-potato routing
  – Each router selects the closest egress point based on
    the path cost in IGP
• BGP decision process
  –   Highest local preference
  –   Shortest AS path
  –   Closest egress point                   dstn
                                                                 B
  –   Arbitrary tie break      A
                                         D
                                                      9
                                     3                    8 10       4
                               4                  3                  G
                                   F 5        8       E
                                         C
         4. Traffic Engineering
                                • How can I pick a route?
                         AS 2   • Local Preference: path
                                  attribute
                                • AS2 wants to prefer fast
LP 80                  LP 100     thick link
                                • Advertisement from right
slow                              router of AS2 has higher
                                  Local Preference
                                • Any BGP router in AS2
                                  will prefer this path
        208.1.1.0/24
                       AS 1
4. Multihoming and Load Balancing
• I want to share traffic between my two providers
• How can I do this?
  4. Load Balancing: Long Prefix
           Match Wins
                         ISP 3
      138.39/16             138.39.1/24




   ISP 1                       ISP 2
 138.39/16                     138.39.1/24
138.39.1/24
                  Customer 138.39.1/24
     4. So How Can I Balance the
               Load?
• Ask my provider to not aggregate my prefix
   – Will this work?
• Split my prefix in two
   – 138.39.1.0/24
   – A: 138.39.1.31/28
   – B: 138.39.1.32/28
• Advertise only one part to ISP2
• ISP2 traffic destined for prefixes in A
• ISP1 traffic destined for prefixes in B
     4. BGP Route Selection Process
1. Maximum prefix length match
2. Highest Local Priority
3. Shortest AS Path
4. Lowest Multi-Exit Discriminator (MED;
   provided routes go through same AS)
5. Min Cost Next hop router (consulting IGP)
6. Prefer external to internal routes
     a. Pick lowest BGP identifier among many E-BGP
     b. Pick lowest BGP identifier among many I-BGP
5. Convergence and Instabilities
• Globally correlated BGP instability is not
  uncommon
• Some causes are well understood
  (misconfiguration, bad path
  announcements)
• Some others are less well understood, and
  more worrisome:
  – worms
             5. Convergence
• There is no guarantee that a BGP configuration
  has a unique routing solution
  – When multiple solutions exist, the (unpredictable)
    order of updates will determine which one wins
• There is no guarantee that a BGP configuration
  has any solution
  – Checking all configurations NP-Complete
• Complex policies (weights, communities setting
  preferences, etc.) increase chances of routing
  anomalies
  – This is the current trend …
                  5. Instabilities
• Most of our understanding arises from empirical
  data (i.e. measurements):
  – Persistent routing loops can and do occur
     • Several hours long (e.g., > 10 hours)
     • Largest: 5 routers
     • All loops intra-domain and arise due to local policies not
       making sense globally
  – Transient routing loops can also arise
     • Last for several seconds
     • Usually occur after outages
  – Erroneous routing can happen
     • E.g. A UK to USA route that goes through Israel was
       observed
        5. Instabilities (cont.)
–   Connectivity may change in mid-stream
    •   Route changes observed during a measurement
    •   Recovery process is temporally bi-modal:
        1. 100’s msec to seconds
        2. order of minutes
–   Route flapping (fluttering)
    •   Rapid route oscillations
    •   Route dampening (give higher preference to known stable
        paths)
–   Instabilities arise due to manual configuration errors
    of BGP speakers, vendor implementation errors
–   Instabilities observed due to worm attack outbreaks
    •   Congestion causes TCP timeouts and correlated “loss” of
        Keepalive messages across significant parts of the Internet
  5. Example of route flapping




Source: Vern Paxson
          5. Open Problems
• BGP is an open and exciting topic
• The community understands very little
• Big open research questions:
  – Better measurements and modelling
  – Robustness, security
  – Network Management: traffic engineering
  – Scalability
  – Rigorous mapping of policies into properties
                    6. Web Sites
1.    http://www.ietf.org
2.    http://www.iana.org
3.    http://www.caida.org
4.    http://bgp.potaroo.net
5.    http://www.isc.org
6.    http://www.sigcomm.org
7.    http://www.cl.cam.ac.uk/~tgg22/interdomain/
8.    http://www.sigcomm.org/ccr/drupal/
9.    http://www.icir.org/
10.   Also use the IEEE Xplore (http://ieeexplore.ieee.org/), ACM
      Digital Library (http://portal.acm.org/dl.cfm), and CiteSeer
      (http://citeseer.ist.psu.edu/cs) web pages for downloading
      papers
                       7. References
•    End-to-end argument
    1.   Saltzer, J. H., Reed, D. P., and Clark, D. D. 1984. End-to-end arguments in
         system design. ACM Trans. Comput. Syst. 2, 4, 277-288.
    2.   Clark, D. D., Sollins, K., Wroclawski, J., and Faber, T. 2003. Addressing
         reality: an architectural response to real-world demands on the evolving
         Internet. SIGCOMM Comput. Commun. Rev. 33, 4, 247-257.
•    Internet topology
    1.   Kleinrock, L., and Kamoun, F. 1977. Hierarchical Routing for Large Networks,
         Performance Evaluation and Optimization, Computer Networks. 1, 3, 155-174.
    2.   Faloutsos, M., Faloutsos, P., and Faloutsos, C. 1999. On power-law
         relationships of the Internet topology. SIGCOMM Comput. Commun. Rev. 29,
         4, 251-262.
    3.   Chen, Q., Chang, H., Govindan, R., and Jamin, S. 2002. The origin of power
         laws in Internet topologies revisited. Proc. IEEE INFOCOM 2002, 2, 608-617.
    4.   Siganos, G., Faloutsos, M., Faloutsos, P., and Faloutsos, C. 2003. Power
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    5.   Mahadevan, P., Krioukov, D., Fomenkov, M., Dimitropoulos, X., Claffy, K.C.,
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         one definitive metric. SIGCOMM Comput. Commun. Rev. 36, 1, 17-26.
                       7. References
•    BGP Dynamics
    1.   Gao, L. and Rexford, J. 2001. Stable internet routing without global
         coordination. IEEE/ACM Trans. Netw. 9, 6, 681-692.
    2.   Paxson, V. 1996. End-to-end routing behavior in the Internet. SIGCOMM
         Comput. Commun. Rev. 26, 4, 25-38.
    3.   Labovitz, C., Malan, G. R., and Jahanian, F. 1997. Internet routing instability.
         Proc. ACM SIGCOMM '97. 115-126.
    4.   Griffin, T. G. and Wilfong, G. 1999. An analysis of BGP convergence
         properties. SIGCOMM Comput. Commun. Rev. 29, 4, 277-288.
    5.   Labovitz, C., Ahuja, A., Wattenhofer, R., and Venkatachary, S. 2001. The
         impact of Internet policy and topology on delayed routing convergence. Proc.
         IEEE INFOCOM 2001. 1, 537-546.
    6.   Griffin, T. G., Shepherd, F. B., and Wilfong, G. 2002. The Stable Paths
         Problem and Interdomain Routing. IEEE/ACM Trans. Netw. 10 2, 232-243.
    7.   Agarwal, S., Chuah, C., Bhattacharyya, S., and Diot, C. 2004. The impact of
         BGP dynamics on intra-domain traffic. SIGMETRICS Perform. Eval. Rev. 32,
         1, 319-330.
    8.   Li, J., Guidero, M., Wu, Z., Purpus, E., and Ehrenkranz, T. 2007. BGP routing
         dynamics revisited. ACM SIGCOMM Comput. Commun. Rev. 37, 2, 5-16.

				
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