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BGP Convergence Measurement Issues

Explore the complexities of BGP convergence measurement within and across autonomous systems, focusing on factors influencing timing, packet flow, and network topology. Learn about best practices for benchmarking approach and optimizing convergence performance.

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BGP Convergence Measurement Issues

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  1. BGP ConvergenceMeasurement Issues Susan Hares, NextHop Padma Krishnaswamy, NextHop Marianne Lepp, Juniper Networks Alvaro Retana, Cisco Howard Berkowitz, Gett Communications Elwyn Davies, Nortel Networks

  2. Tester Tester Internet-wide Convergence? AS Flapping AS He's Dead, Jim AS AS AS AS

  3. Tester Tester AS-wide iBGP Convergence: Within an AS Single AS R R R

  4. Convergence: Within a Box Single Box Tester Tester Routing/Control Forwarding

  5. Convergence for BMWG • Box wide • eBGP initially • Control Plane initially • Black box • Specify begin and end of convergence measurement • Specify measurement point

  6. Send a packet stream from TR – 3 Measurements • Convergence 1: 1st packet sent from Test Generator to 1st packet received by Test Collector • Transmission in and out plus process time of 1st packet • Convergence 2: Last Packet sent from Test Generator to last packet received by Test Collector • Transmission in, queuing, processing of preceding updates, tail end processing, transmission out of last packet • Convergence 3: 1st packet sent from Test Generator to last packet received by Test Collector • Transmission in and out (relative to DUT), plus back-up in BGP update and processing of entire stream

  7. Measurement 1-3: Factors • Packing matters • Influences number of packets in the train • Attribute packing • Classification speed • Packetization triggers • IBGP synchronization turned off • Turn off Minimum Route Advertisement Interval Timers • Smoothing in BGP to avoid self-synchronization in the Network

  8. BGP Convergence Depends On … • Route mixtures • Packet packing • Timers • TCP implementations • Peers types, number of peers, and connectivity • BGP-specific functionality • Eg. Confederations, use of route reflectors, etc. • Topology • Vantage point within the network • Policy

  9. Benchmarking Convergence Approach • Must be repeatable • Must be consistent • Must be specifiable • Must take into account • Route mixture (data) • Peers types and connectivity • BGP-specific functionality • Topology

  10. Goals • Provide a baseline of expected performance in today’s network. • Test different vendor implementations fairly • Design tests that can be replicated • Good results require good data • The amount, type and composition of the information advertised to the DUT has an impact on the convergence.

  11. Route Mixtures

  12. Modeling Route Mixtures: Why not just use a feed? • The route mixture is highly dependent on the vantage point – Tier 1 ISP, Enterprise, Access, etc. • Problems with Looking Glass • Vantage point • Need to test tables larger than current live tables • Needs to be repeatable, consistent, and specifiable

  13. Route Mixture • Factors that describe the BGP Table: composition and timing • Prefix distribution • Node distribution and levels on tree • AS mixtures and path lengths • Attribute distribution (nexthop, communities,MED, localpref) • Packet packing • Update sequencing (timing) • Packet trains

  14. Prefix Distribution • Example: A table of all /32s is not representative of the real world • Prefixes are distributed across dozens of prefix lengths • For IPv4, the distribution is spread out through the Class A, B, and C address spaces. • For IPv6, there is no data • Need to describe prefix distribution per prefix length • Better characterization for IPv4 if Class also taken into account • Analyze current Internet table to determine prefix distribution characteristics

  15. Prefix Distribution • Example percentages of prefix distribution: • Mask   Overall   Class A   Class B   Class C •      16   0.08114   0.00076   0.06637   0.01401     17   0.00912   0.00030   0.00142   0.00741     18   0.01813   0.00093   0.00113   0.01607     19   0.05910   0.00378   0.00196   0.05336     20   0.03372   0.00152   0.00151   0.03070     21   0.04128   0.00085   0.00127   0.03915     22   0.05574   0.00171   0.00226   0.05176     23   0.07878   0.00235   0.00450   0.07193     24   0.53355   0.00892   0.02366   0.50097 Total prefix length distribution. IPv4 sample distribution across classes.

  16. IP v6 Prefix Distribution • Example percentages of prefix distribution: • Mask   Overall   3FEE 2001 other •   0-10    0.08114   0.00076   0.06637   0.01401  11-20   0.00912   0.00030   0.00142   0.00741  21-30 0.01813   0.00093   0.00113   0.01607  31-40   0.05910   0.00378   0.00196   0.05336  41-50   0.03372   0.00152   0.00151   0.03070  51-60   0.04128   0.00085   0.00127   0.03915  61-70   0.05574   0.00171   0.00226   0.05176  71-80   0.07878   0.00235   0.00450   0.07193  81-90  0.53355   0.00892   0.02366   0.50097 • 91-100  0.53355   0.00892   0.02366   0.50097 • 100-110 0.53355   0.00892   0.02366   0.50097 • 111-128 0.53355   0.00892   0.02366   0.50097 IPv6 sample distribution across currently routed Addres space Total prefix length distribution.

  17. Node Distribution • Is tree dependent • Width and depth of table are important • Route mixtures should exercise various choices of trees • A route mixture that minimizes the number of nodes is not accurate • A route mixture that maximizes the spread of prefixes creates is not accurate

  18. Node Distribution Levels Nodes

  19. IP v6 Node Distribution Levels ROOT 3FEE:: 2001:: 2001::01 2001:02 3FEE:0100 3FEE:2000:: 3FEE:0101 3FEE:0101 2001:0201 2001:0201:02 2001:0201:01 3FEE:0101:01 Nodes

  20. ROOT ROOT 1.0.0.0 2.0.0.0 3.0.0.0 1.0.0.0 1.1.0.0 2.1.0.0 3.1.0.0 1.1.0.0 1.1.1.0 2.1.1.0 3.1.1.0 1.1.1.0 1.1.1.1 2.1.1.1 3.1.1.1 1.1.1.1 1.1.1.2 1.1.1.2 Node Distribution • For example, the following tables both contain three Class A /32 prefixes • Table A 1.1.1.1/32, 1.1.1.2/32, 1.1.1.3/32 • Table B 1.1.1.1/32, 2.1.1.1/32, 3.1.1.1/32 • Their distribution in a tree will be different. • Table A represents a narrow distribution, while Table B represents a wide distribution. Table B Table A

  21. Node Distribution Summary • The width of the table must be measured per prefix distribution and length • Need to determine how many nodes each address/prefix length combination use in a real table • Solution: Analyze current Internet table to determine node distribution characteristics

  22. Route Components

  23. BGP Attribute Distribution • A BGP table contains many “attribute combinations” • Analysis shows: • 11.75% of the routes have a unique AS_PATH • 2.5% of the routes have some other unique attribute.  • 0.25% of the table have both a unique AS_PATH and some other unique attribute

  24. BGP Attribute Distribution • Prefixes that share an attribute are not necessarily grouped together • Analysis shows an average of two consecutive NLRI share the same attribute combination • 1.0.0.0/8 AS_PATH 100 200 • 2.0.0.0/8 AS_PATH 100 200 • 3.0.0.0/8 AS_PATH 200 300 • 4.0.0.0/8 AS_PATH 200 300 • 5.0.0.0/8 AS_PATH 200 300 • 6.0.0.0/8 AS_PATH 100 200

  25. Planes (control),Trains,and no Automobiles

  26. Packet Packing • Each packet has attributes and NLRIs • Attribute packing is the ability to detect and pack NRLIs with the same attributes into a packet • NLRI packing is: • the number of NLRIs per packet • MPBGP not considered for 1st draft • IPv6 packing is not different than IPv4 • Multicast packing (IP v4 and IP v6) may impact packing • Specifics are affected by implementation

  27. Update Sequencing (Timing) • Parameters are: • Number of packets in a train • Interval between packets in a train • TCP parameters, traffic and implementations affect this Packet 1 Packet 2 Packet 3 Packet 4 Packet train Packet train

  28. Timers • Key timers • Min-Route Advertisement Interval, Min AS Originations Interval --best setting still in debate • Route Flap damping mechanisms • Implementations vary • Shorter prefixes get less damping • RIPE 229 suggest parameters • 1st Bgp Conv draft mandates route flap damping off • TCP settings • Operators need to give feedback

  29. Peers, not Beers

  30. Peer type matters • EBGP vs IBGP • EBGP • 3rd party versus 1st party nexthop • promiscuous versus specific peering • IBGP - Route Reflection client and Confederations affect convergence patterns • See ietf-idr-route-oscillations-01.txt • Still single box but these affect work done by box

  31. Multiple Peers in test Environment • Peers can have staggered starts • Most realistic • Peers can all send simultaneously • Most load on the router • Peers can have staggered starts in groups

  32. Sample topology with 4 Peers tcpdump tcpdump TG1 DUT TC TG2 tcpdump TG3 tcpdump TG4 tcpdump

  33. Peer Specifics • Type of Peer • Promiscuous/Specific • Sequence • Connection establishment • Sending 1st data • Spacing of updates • Connection up/down

  34. Timing & Synchronization • Consistency among timestamps taken by different devices is a requirement • Should be at least 1 order of magnitude better than measured quantity • For BGP convergence, we are time-stamping packets • NTP? GPS? Other? • Synchronization between measurements can a significant factor

  35. Some Boxes workHarder than Others

  36. BGP Protocol functions will impact convergence • Route Reflections, • Confederations • Add/delete communities • RFC 2547, Label switching • Multi-protocol • Route flap damping • Min Route Advertisement

  37. Parameters we suggest for Protocol Functions for 1st Document • No Route Reflectors (no IBGP this version) • No confederations • No Add/Delete communities • No 2547 VPNS or multicast • Route flap damping OFF • Min Route Advertisement Interval specified • Min AS Origination Interval specified

  38. Topology

  39. Topology matters • Exchange point topology • N star topologies meshed for Route Reflection • Confederations with particular topologies • IBGP/EBGP mesh overlay • Building blocks • single link, line, mesh, partial mesh, star, wheel

  40. …… Single link: 1st Document TR1 TRes DUT TR2 line TRn n >= 1

  41. Line DUT TR1 DUT DUT Longer line TRes

  42. Mesh DUT DUT TRes TR1 DUT DUT mesh TRes TRes

  43. Partial Mesh DUT DUT TRes TR1 DUT DUT TRes TRes

  44. References • IETF51 BMWG talk: http://www.ietf.org/proceedings/01aug/slides/bmwg-4/ • NextHop IETF51 talk: http://www.ietf.org/proceedings/01aug/slides/bmwg-5/index.html • Howard’s IETF51 talk: http://www.ietf.org/proceedings/01aug/slides/bmwg-6/index.html • Recommendations for flap damping, Ripe 229: http://www.ripe.net/ripe/docs/ripe-229.html • BGP Convergence Terminology ID: http://www.ietf.org/internet-drafts/draft-ietf-bmwg-conterm-00.txt • BGP Convergence Methodology: http://www.ietf.org/internet-drafts/draft-ietf-bmwg-bgpbas-00.txt

  45. Thank You Questions?

  46. Route Mixtures Matter! • The amount, type and composition of the information advertised to the DUT has an impact on the convergence. • Goal is to provide a baseline of expected performance in today’s network. • Test different vendor implementations fairly • Design tests that can be replicated • Good results require good data

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