DYNAMICS OF PREFIX USAGE AT AN EDGE ROUTERKaustubh Gadkari, Dan Massey and Christos Papadopoulos

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Outline Introduction – BGP RIB and FIB growth Motivation Methodology Results Conclusions and future work

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Outline Introduction – BGP RIB and FIB growth Motivation Methodology Results Conclusions and future work

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Inter-Domain Routing

CSU

129.82/16, 129.82/18 …

Google

74.125/16, …

BGP

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BGP TablesRouter Memory

Routing Table(RIB)

Routing Updates Routing Updates

Forwarding Table(FIB)

Line Card Line Card Line Card

(Prefix, Path)

Forwarding Table(FIB)

Forwarding Table(FIB)

(Prefix, Outgoing Interface, Next

Hop)

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Outline Introduction – BGP RIB and FIB growth Motivation Methodology Results Conclusions and future work

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Table Growth The size of the

global routing is growing rapidly.

Increasing routing table size requires more memory on routers.

Operators are forced into faster upgrade cycles.

http://bgp.potaroo.net/as6447/

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Implications of Table Growth RIB size affects FIB size.

FIB scaling is arguably more important. FIBs stored on line card memory, which is

smaller and more expensive than main memory.

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Outline Introduction – BGP RIB and FIB growth Motivation Methodology Results Conclusions and future work

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Motivation Some current research focuses on scaling the

FIB by storing partial forwarding information.

But how to choose prefixes in a reduced FIBs? Prefixes receiving most packets should probably

be in the table. But are there better criteria to define a dominant

set? How does it behave?

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Motivation (contd.) Previous work focused on prefix popularity

over days or weeks. Tradeoff that prefers ease of selection.

Optimum prefix selection is a hard problem. Factors: traffic volume, activity patterns and

interplay of traffic dynamics

This work: understand prefix dynamics better.

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Outline Introduction – BGP RIB and FIB growth Motivation Methodology Results Conclusions and future work

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Methodology Monitor links to two tier-1 provider links

(1Gb/s each) at a regional ISP.

Dataset: two simultaneous 24-hour packet traces from these links.

Use outgoing packets only.

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Old Metric: Global Rank Rank prefixes

according to number of packets during the full 24-hour trace. This is the prefix’s

global rank.

Plot number of prefixes that account for a given fraction of packets.

Results corroborate previous studies.

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Measuring Prefix Dynamics Split traffic trace into small intervals (5

min).

Rank prefixes in each interval according to number of packets. We call this the prefix’s interval rank.

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New Metrics Duty cycle

Fraction of the total number of intervals in which the prefix receives at least one packet.

Mean rank difference Variation of a prefix’s interval rank from its

global rank.

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Outline Introduction – BGP RIB and FIB growth Motivation Methodology Results Conclusions and future work

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Duty Cycle Measure of prefix’s activity.High

duty cycle, high

traffic

Low duty

cycle, low

traffic

~200 prefixes

~56,000

prefixes

High duty

cycle, low

traffic

~24,000

prefixes

Low duty cycle, high

traffic

~10 prefixes

Global Prefix Rank

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Duty Cycle Observations Popular prefixes have high duty cycles.

Always get packets.

Several popular prefixes have a duty cycle of > 90%.

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Mean Rank Difference Measure of prefix’s “busy-ness”.

Stable Prefixes

Less than 1% of all prefixes,

40% of all packets

Generally Popular Prefixes5% of all prefixes, 55% of

all packets

Generally Unpopular Prefixes

60% of all

prefixes, 5% of all

traffic

Global Prefix Rank

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Outline Introduction – BGP RIB and FIB growth Motivation Methodology Results Conclusions and future work

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Conclusions Understanding dynamic behavior of FIB prefixes is

important for reduced-FIB designs. Proposed two new metrics: Duty cycle and mean

rank difference We corroborated previous work showing set of

dominant prefixes is small. New metrics characterize the dominant set better,

which is generally active and busy. Majority of the prefixes have very low activity opening

up caching opportunities. Results encouraging in terms of developing

reduced FIB designs.

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Future Work Investigate prefix dynamics at other

ISPs.

Investigate prefix dynamics at different intervals.

Develop a design for efficient forwarding using a reduced FIB.