BGP table fragmentation: what & who? Julien Gamba Romain Fontugne, Cristel Pelsser, Randy Bush, Emile Aben University of Strasbourg 1 Why looking at fragmentation? 647 000 2 Why looking at fragmentation? 647 000 Amount of IP prefixes announced on the Internet (and counting) 2 Why looking at fragmentation? 647 000 Amount of IP prefixes announced on the Internet (and counting) • Large routing tables consume memory • Routers memory (TCAM) is expensive, so they do not have a lot of it (especially the older ones) • Too many routes means routers slowing down or shutting down 2 Why looking at fragmentation? • Some of these prefixes are fragmented and could be aggregated 3 Why looking at fragmentation? • Some of these prefixes are fragmented and could be aggregated • Some of these prefixes are redundant and could be removed from the routing table 3 Why looking at fragmentation? • Some of these prefixes are fragmented and could be aggregated • Some of these prefixes are redundant and could be removed from the routing table • How bad is the fragmentation? • How many prefixes are redundant? • What are the causes of all this? 3 IP prefixes classification • Top: is covering some smaller prefix(es); • Deaggregated: is covered by another prefix which is originated by the same AS; • Delegated: is covered by another prefix which is originated by another AS; • Lonely: does not overlap with any other prefix. Luca Cittadini et al. (2010). “Evolution of Internet Address Space Deaggregation: Myths and Reality”. In: IEEE journal on selected areas in communications 4 IP prefixes classification • Top: is covering some smaller prefix(es); • Deaggregated: is covered by another prefix which is originated by the same AS; • Delegated: is covered by another prefix which is originated by another AS; • Lonely: does not overlap with any other prefix. Luca Cittadini et al. (2010). “Evolution of Internet Address Space Deaggregation: Myths and Reality”. In: IEEE journal on selected areas in communications 5 IP prefixes classification • Top: is covering some smaller prefix(es); • Deaggregated: is covered by another prefix which is originated by the same AS; • Delegated: is covered by another prefix which is originated by another AS; • Lonely: does not overlap with any other prefix. Luca Cittadini et al. (2010). “Evolution of Internet Address Space Deaggregation: Myths and Reality”. In: IEEE journal on selected areas in communications 6 IP prefixes classification • Top: is covering some smaller prefix(es); • Deaggregated: is covered by another prefix which is originated by the same AS; • Delegated: is covered by another prefix which is originated by another AS; • Lonely: does not overlap with any other prefix. Luca Cittadini et al. (2010). “Evolution of Internet Address Space Deaggregation: Myths and Reality”. In: IEEE journal on selected areas in communications 7 IP prefixes classification • Top: is covering some smaller prefix(es); • Deaggregated: is covered by another prefix which is originated by the same AS; • Delegated: is covered by another prefix which is originated by another AS; • Lonely: does not overlap with any other prefix. Luca Cittadini et al. (2010). “Evolution of Internet Address Space Deaggregation: Myths and Reality”. In: IEEE journal on selected areas in communications 8 Deaggregation evolution — prefixes • routeviews data, as seen by AS 3356 (Level3), counting prefixes Evolution of prefixes classification - IPv4 Percentage of prefixes 50 40 30 • Proportion of deaggregated is increasing over time 20 10 0 2002 2004 2006 Deaggregated Delegated 2008 2010 Year 2012 Lonely Top 2014 2016 • Combined fraction of deaggregated and delegated prefixes is constant AS10 AS10 AS20 AS30 10.1/16 10.1.1/24 10.1.2/24 10.2/16 Top Deaggregated Delegated Lonely 9 Deaggregation evolution — addresses Evolution of IPv4 addresses classification Percentage of addresses 60 • Deaggregated addresses are still increasing, top addresses are increasing too 50 40 30 20 • Lonely addresses are decreasing 10 0 2002 2004 2006 Deaggregated Delegated 2008 2010 Year 2012 2014 2016 Lonely Top routeviews data, as seen by AS 3356 (Level3) AS10 AS10 AS20 AS30 10.1/16 10.1.1/24 10.1.2/24 10.2/16 Top Deaggregated Delegated Lonely 10 Deaggregation evolution In other words • There are more and more deaggregated prefixes • Combined fraction of deaggregated and delegated prefixes is constant • The proportion of lonely addresses is decreasing, while top and deaggregated increase 11 Deaggregation evolution In other words • There are more and more deaggregated prefixes • Combined fraction of deaggregated and delegated prefixes is constant • The proportion of lonely addresses is decreasing, while top and deaggregated increase What is going on? • Are lonely prefixes becoming top? Deaggregated? • Do they disappear? Is there just less new lonely prefixes? • What are the movements between the categories? What is the stability of the prefixes? 11 Prefixes dynamics Movements between categories del 2001 del 2002 del 2003 del 2004 del 2005 del 2006 del 2007 del 2008 del 2009 del 2010 del 2011 del 2012 del 2013 del 2014 del 2015 del 2016 dea 2001 dea 2002 dea 2003 dea 2004 dea 2005 dea 2006 dea 2007 dea 2008 dea 2009 dea 2010 dea 2011 dea 2012 dea 2013 dea 2014 dea 2015 dea 2016 lon 2001 lon 2002 lon 2003 lon 2004 lon 2005 lon 2006 lon 2007 lon 2008 lon 2009 lon 2010 lon 2011 lon 2012 lon 2013 lon 2014 lon 2015 lon 2016 top 2001 top 2002 top 2003 top 2004 top 2005 top 2006 top 2007 top 2008 top 2009 top 2010 top 2011 top 2012 top 2013 top 2014 top 2015 top 2016 Most movements appear between lonely and deaggregated prefixes, both ways Lonely prefixes become deaggregated when the covering prefix is announced 12 Prefixes disappearances • Counting how many prefixes disappear from the RIB between two months Prefix disappearing over time Percentage of prefixes 3 2.5 2 • Graph show average per year 1.5 1 0.5 0 2002 2004 2006 Deaggregated Delegated 2008 2010 Year 2012 2014 2016 Lonely Top routeviews data, as seen by AS 3356 (Level3) • Same trend across categories, although deaggregated prefixes disappear more AS10 AS10 AS20 AS30 10.1/16 10.1.1/24 10.1.2/24 10.2/16 Top Deaggregated Delegated Lonely 13 Stability of prefixes Deaggregated prefixes seems to be the most volatile kind: • Why is that? • Is it traffic engineering? • Is it something else? 14 Detection of traffic engineering AS path prepending • Graph shows average per year Proportion of prefixes using path prepending Percentage by category 40 a 35 30 25 20 15 • Showing the proportion of prefixes announced using path prepending in each category 10 5 0 2002 2004 2006 Deaggregated Delegated 2008 2010 Year 2012 2014 2016 Lonely Top routeviews data, as seen by AS 3356 (Level3) • Path prepending usage is slowly increasing • No clear trend between categories AS10 AS10 AS20 AS30 10.1/16 10.1.1/24 10.1.2/24 10.2/16 Top Deaggregated Delegated Lonely 15 Selective announcements • Graph shows average per year Use of selective announcements Percentage of prefixes 25 • Showing the proportion of prefixes seen by less than half the peers by category 20 15 10 5 0 2002 2004 2006 Deaggregated Delegated 2008 2010 Time 2012 Lonely Top 2014 2016 • Lonely and deaggregated prefixes are the categories that use selective announcements the most AS10 AS10 AS20 AS30 10.1/16 10.1.1/24 10.1.2/24 10.2/16 Top Deaggregated Delegated Lonely 16 Who is engineering traffic? • Graph shows proportion of deaggregated prefixes by AS business type Cumulative distribution fonction 1 0.8 0.6 • Large transit AS list comes from CAIDA’s classification 0.4 0.2 Large transit (30) Content (137) Others (53564) 0 0 20 40 60 80 Percentage of deaggregated prefixes per AS 100 • Large transit providers may split their address space to do traffic engineering AS10 AS10 AS20 AS30 10.1/16 10.1.1/24 10.1.2/24 10.2/16 Top Deaggregated Delegated Lonely 17 Aggregability of lonely prefixes Aggregables lonely prefixes 300000 Two prefixes are aggregables if: Number of prefixes 250000 200000 • they have the same AS origin 150000 • they are consecutive 100000 50000 0 2002 2004 2006 All lonely prefixes With aggregation 2008 2010 Year 2012 2014 2016 • the aggregate falls on a power of two boundary Difference routeviews data, as seen by AS 3356 (Level3) AS10 AS10 AS20 AS30 10.1/16 10.1.1/24 10.1.2/24 10.2/16 Top Deaggregated Delegated Lonely 18 In conclusion • Deaggregation has been increasing for the last fifteen years • Combined fraction of deaggregated and delegated prefixes is constant • Some large transit AS split heavily their address space 19 In conclusion • Deaggregation has been increasing for the last fifteen years • Combined fraction of deaggregated and delegated prefixes is constant • Some large transit AS split heavily their address space We still don’t know: • why the heavy splitting? • for traffic engineering? • for security? 19 Questions?
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