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Congestion Mitigation

Congestion Mitigation. Trying to maximise performance between MFN’s network and a peer’s network over some busy PNIs. Hello, Good Evening. Joe Abley jabley@mfnx.net Toolmaker, Token Canadian Metromedia Fiber Network. Background.

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Congestion Mitigation

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  1. Congestion Mitigation Trying to maximise performance between MFN’s network and a peer’s network over some busy PNIs

  2. Hello, Good Evening Joe Abley jabley@mfnx.net Toolmaker, Token Canadian Metromedia Fiber Network

  3. Background • There are frequent periods of congestion between our network and a peer’s network in Europe • The peer is a major operator in the region, and evil forces are preventing us from simply lighting up new fibre • We need to work with what we have in place already

  4. Characteristics of Problem • The peer is home to a lot of broadband subscribers • Transient hot-spots in content hosted within MFN’s network cause localised congestion in some PNIs, with other PNIs showing headroom • We get paid for shifting packets (if we don’t carry the packets, we don’t get paid)

  5. State of Play: Day One

  6. Goals • Identify the important consumers of traffic in and beyond the peer’s network • Once we can characterise the major traffic sinks, we can try and balance them out across our various PNIs • Hopefully this will make the PNIs less sensitive to bursty traffic • We expect to have to keep measuring and rebalancing

  7. Tools • Ixia IxTraffic • Gumption • Unix-based BGP speaker that participates in the IBGP mesh • Gives us route history • SeeFlow • Smart NetFlow collector which talks to Gumption • Awk • We always have awk

  8. Infrastructure • NetFlow traffic to be collected in-band from GSR12012s • Single IxTraffic box: • FreeBSD 4.5, i386, dual 700MHz P3, 2GB RAM • Overkill • Load average occasionally peaks above 0.07 • 10GB filesystem for storing routing and flow data in • Located in Virginia • MRTG-like thing (duck) which also lives in VA on a different box gives us nice visibility of congestion trends

  9. Exporting Flow Data • Flow switching needs to be turned on in a maint window, because it makes the routers belch impolitely • All interfaces that can contribute towards traffic sent towards the peer get “ip route-cache flow sampled” • See kiddie script! See router die! • Export config is trivial: ip flow-export source Loopback0 ip flow-export version 5 peer-as ip flow-export destination 192.168.38.9 3871 ip flow-sampling-mode packet-interval 1000 • Note low sampling rate of 1:1000.

  10. Collecting Flow Data • SeeFlow is configured to populate net2net and aspath matrices (“buckets”) • We suspect that a lot of data is getting sunk within the peer network, hence net2net • We could be wrong, and aspath matrices are cool, so we collect those too • Buckets chew up about 50MB of disk per day (all routers)

  11. Initial Discoveries • All the traffic is being sunk within the peer network, and not in a downstream network • Damn • All the traffic is being sunk into a single /12 advertisement • Damn • We need better granularity if we are going to be able to spread the demand across our PNIs

  12. ASPATH Matrices [jabley@nautilus]$ seeasp -s 3320 ./dtag.agg | more Facets: TimeInterval : 05/09/2002 15:00:03.663492 - 06/05/2002 04:57:58.747866 PDT SuperDataFacet : Facets: RouterIpv4Addr : 209.249.254.142 RouterName : pr1.fra1.de.mfnx.net Facets: RouterIpv4Addr : 209.249.254.195 RouterName : mpr2.vie3.at.mfnx.net Facets: RouterIpv4Addr : 216.200.254.246 RouterName : mpr1.ams1.nl.mfnx.net AS P PktsThru BytesThru PktsTo BytesTo PktsTotal BytesTotal ----- - ---------- ------------ ---------- ------------ ---------- ------------ 0 - 0 0 371.203M 143.286G 371.203M 143.286G AAAA P 1.816M 333.567M 108.112M 36.705G 109.928M 37.038G BBBB - 0 0 1.516M 191.657M 1.516M 191.657M CCCC - 0 0 33.173K 23.932M 33.173K 23.932M DDDD - 9 5.118K 35.555K 23.064M 35.564K 23.069M EEEE - 12.567K 7.998M 3.663K 2.413M 16.230K 10.411M FFFF - 917 704.260K 16.872K 9.642M 17.789K 10.346M GGGG - 2.187K 1.406M 22.323K 8.250M 24.510K 9.656M HHHH - 0 0 30.447K 8.587M 30.447K 8.587M IIII - 0 0 10.658K 7.427M 10.658K 7.427M JJJJ - 0 0 27.932K 7.029M 27.932K 7.029M

  13. Net2Net Matrices 172.184.0.0/13 -> A.A.0.0/12 13001989 5601247858 172.184.0.0/13 -> A.A.0.0/12 12983375 5592070913 62.4.67.0/24 -> B.B.0.0/11 9459634 1687041555 62.4.67.0/24 -> B.B.0.0/11 9443861 1677536483 172.176.0.0/14 -> A.A.0.0/12 7113026 2985029679 172.176.0.0/14 -> A.A.0.0/12 7099648 2977787074 62.80.115.0/24 -> C.C.0.0/11 6873518 1236318991 62.4.67.0/24 -> A.A.0.0/12 6689319 1180741686 62.4.82.0/24 -> A.A.0.0/12 6611879 1171430532 62.4.67.0/24 -> C.C.0.0/11 3469776 629221553 62.4.82.0/24 -> C.C.0.0/11 3433970 625422145 62.4.67.0/24 -> D.0.0.0/13 2422913 442942807 62.4.67.0/24 -> D.0.0.0/13 2407651 470778890 62.4.65.96/27 -> A.A.0.0/12 1981446 287218317 62.80.116.0/24 -> E.E.0.0/15 1802114 378062358 62.4.67.0/24 -> F.F.0.0/14 1510412 315282857 62.4.67.0/24 -> F.F.0.0/14 1421497 277014582 62.4.65.96/27 -> B.B.0.0/11 1341063 378931389 62.4.81.128/27 -> B.B.0.0/11 1330058 378268227 172.185.0.0/16 -> A.A.0.0/12 1077841 446966211 172.185.0.0/16 -> A.A.0.0/12 1073445 443555367

  14. Destination Prefix Histogram destination net megabytes proportion A.A.0.0/12 21478 59% B.B.0.0/11 6494 18% C.C.0.0/11 4388 12% D.0.0.0/13 1365 3% F.F.0.0/14 1033 2% G.G.0.0/15 416 1% H.H.0.0/14 311 0% I.I.I.0/21 160 0% J.J.0.0/15 117 0% K.K.0.0/19 89 0%

  15. Drilling down into A.A.0.0/12 • Ask peer to advertise longer prefixes within the /12, so we can measure the traffic per prefix • Wait for response • GOTO 10 • Maybe we can fix this ourselves

  16. /home/dlr/bin/bgpd • We injected 15 covered /16 prefixes into IBGP, with a NEXT_HOP that lay within the remaining /16 • All tagged no-export, to avoid messing with the peer’s public route policy • Strictly local-use within AS6461

  17. More Collection • The increased granularity gives us better visibility into the traffic sinks within the peer network • We will try to spread the traffic over the available PNIs so we can weather bursts of demand more effectively • We will also continue to let the peer know what we are doing • You never know, they may be listening

  18. New Dest Prefix Histogram destination net megabytes proportion B.B.0.0/11 1912 14% A.76.0.0/16 1530 11% C.C.0.0/11 1516 11% A.73.0.0/16 1120 8% A.72.0.0/16 1024 7% A.64.0.0/12 874 6% A.74.0.0/16 683 5% A.70.0.0/16 696 5% A.68.0.0/16 601 4% A.66.0.0/16 437 3%

  19. State of Play: Day N

  20. Conclusions • “Light more fibre” is not always a realistic strategy • You are not always your peer’s number one priority, so it’s nice to be able to take matters into your own hands • Distributing the heavy traffic sinks across different PNIs makes bursty demand less unpleasant • Routing plus flow data = Power. Or something.

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