Simple Multihoming. ISP Training Workshops

Transcription

1 Simple Multihomig ISP Traiig Workshops 1

2 Why Multihome? p Redudacy Oe coectio to iteret meas the etwork is depedet o: p Local router (cofiguratio, software, hardware) p WAN media (physical failure, carrier failure) p Upstream Service Provider (cofiguratio, software, hardware) 2

3 Why Multihome? p Reliability Busiess critical applicatios demad cotiuous availability Lack of redudacy implies lack of reliability implies loss of reveue 3

4 Why Multihome? p Supplier Diversity May busiesses demad supplier diversity as a matter of course Iteret coectio from two or more suppliers p With two or more diverse WAN paths p With two or more exit poits p With two or more iteratioal coectios p Two of everythig 4

5 Why Multihome? p Not really a reaso, but oft quoted p Leverage: Playig oe ISP off agaist the other for: p Service Quality p Service Offerigs p Availability 5

6 Why Multihome? p Summary: Multihomig is easy to demad as requiremet of ay operatio But what does it really mea: p I real life? p For the etwork? p For the Iteret? Ad how do we do it? 6

7 Multihomig Defiitio p More tha oe lik exteral to the local etwork two or more liks to the same ISP two or more liks to differet ISPs p Usually two exteral facig routers oe router gives lik ad provider redudacy oly 7

8 Multihomig p The scearios described here apply equally well to ed sites beig customers of ISPs ad ISPs beig customers of other ISPs p Implemetatio detail may be differet ed site ISP ISP1 ISP2 ISP cotrols cofig ISPs share cofig 8

9 Autoomous System Number (ASN) p Two rages (origial 16-bit rage) (32-bit rage RFC4893) p Usage: 0 ad (reserved) (public Iteret) (documetatio RFC5398) (private use oly) (represet 32-bit rage i 16-bit world) (documetatio RFC5398) (public Iteret) p 32-bit rage represetatio specified i RFC5396 Defies asplai (traditioal format) as stadard otatio 9

10 Autoomous System Number (ASN) p ASNs are distributed by the Regioal Iteret Registries They are also available from upstream ISPs who are members of oe of the RIRs p Curret 16-bit ASN allocatios up to have bee made to the RIRs Aroud are visible o the Iteret p Each RIR has also received a block of 32-bit ASNs Out of 3100 assigmets, aroud 2800 are visible o the Iteret p See 10

11 Private-AS Applicatio p Applicatios -or A ISP with customers multihomed o their backboe (RFC2270) A corporate etwork with several regios but coectios to the Iteret oly i the core -or Withi a BGP Cofederatio / /24 C / B /24 A /

12 Private-AS Removal p Private ASNs MUST be removed from all prefixes aouced to the public Iteret Iclude cofiguratio to remove private ASNs i the ebgp template p As with RFC1918 address space, private ASNs are iteded for iteral use They should ot be leaked to the public Iteret p Cisco IOS eighbor x.x.x.x remove-private-as 12

13 Trasit/Peerig/Default p Trasit Carryig traffic across a etwork Usually for a fee p Peerig Exchagig locally sourced routig iformatio ad traffic Usually for o fee Sometimes called settlemet free peerig p Default Where to sed traffic whe there is o explicit match i the routig table

14 Cofigurig Policy p Assumptios: prefix-lists are used throughout easier/better/faster tha access-lists p Three BASIC Priciples prefix-lists to filter prefixes filter-lists to filter ASNs route-maps to apply policy p Route-maps ca be used for filterig, but this is more advaced cofiguratio 14

15 Policy Tools p Local preferece outboud traffic flows p Metric (MED) iboud traffic flows (local scope) p AS-PATH preped iboud traffic flows (Iteret scope) p Commuities specific iter-provider peerig 15

16 Origiatig Prefixes: Assumptios p MUST aouce assiged address block to Iteret p MAY also aouce subprefixes reachability is ot guarateed p Curret miimum allocatio is from /20 to /24 depedig o the RIR Several ISPs filter RIR blocks o this boudary Several ISPs filter the rest of address space accordig to the IANA assigmets This activity is called Net Police by some 16

17 Origiatig Prefixes p p p The RIRs publish their miimum allocatio sizes per /8 address block AfriNIC: APNIC: ARIN: LACNIC: lacic.et/e/registro/idex.html RIPE NCC: Note that AfriNIC oly publishes its curret miimum allocatio size, ot the allocatio size for its address blocks IANA publishes the address space it has assiged to ed-sites ad allocated to the RIRs: Several ISPs use this published iformatio to filter prefixes o: What should be routed (from IANA) The miimum allocatio size from the RIRs

18 Net Police prefix list issues p p p p p Meat to puish ISPs who pollute the routig table with specifics rather tha aoucig aggregates Impacts legitimate multihomig especially at the Iteret s edge Impacts regios where domestic backboe is uavailable or costs $$$ compared with iteratioal badwidth Hard to maitai requires updatig whe RIRs start allocatig from ew address blocks Do t do it uless cosequeces uderstood ad you are prepared to keep the list curret Cosider usig the Team Cymru or other reputable bogo BGP feed: 18

19 How to Multihome Some choices 19

20 Trasits p Trasit provider is aother autoomous system which is used to provide the local etwork with access to other etworks Might be local or regioal oly But more usually the whole Iteret p Trasit providers eed to be chose wisely: Oly oe p o redudacy Too may p more difficult to load balace p o ecoomy of scale (costs more per Mbps) p hard to provide service quality p Recommedatio: at least two, o more tha three

21 Commo Mistakes p ISPs sig up with too may trasit providers Lots of small circuits (cost more per Mbps tha larger oes) Trasit rates per Mbps reduce with icreasig trasit badwidth purchased Hard to implemet reliable traffic egieerig that does t eed daily fie tuig depedig o customer activities p No diversity Chose trasit providers all reached over same satellite or same submarie cable Chose trasit providers have poor oward trasit ad peerig

22 Peers p A peer is aother autoomous system with which the local etwork has agreed to exchage locally sourced routes ad traffic p Private peer Private lik betwee two providers for the purpose of itercoectig p Public peer Iteret Exchage Poit, where providers meet ad freely decide who they will itercoect with p Recommedatio: peer as much as possible!

23 Commo Mistakes p Mistakig a trasit provider s Exchage busiess for a o-cost public peerig poit p Not workig hard to get as much peerig as possible Physically ear a peerig poit (IXP) but ot preset at it (Trasit sometimes is cheaper tha peerig!!) p Igorig/avoidig competitors because they are competitio Eve though potetially valuable peerig parter to give customers a better experiece

24 Multihomig Scearios p Stub etwork p Multi-homed stub etwork p Multi-homed etwork p Multiple Sessios to aother AS 24

25 Stub Network AS101 AS100 p No eed for BGP p Poit static default to upstream ISP p Upstream ISP advertises stub etwork p Policy cofied withi upstream ISP s policy

26 Multi-homed Stub Network AS100 AS65530 p Use BGP (ot IGP or static) to loadshare p Use private AS (ASN > 64511) p Upstream ISP advertises stub etwork p Policy cofied withi upstream ISP s policy

27 Multi-homed Network AS300 Global Iteret AS200 AS100 p May situatios possible multiple sessios to same ISP secodary for backup oly load-share betwee primary ad secodary selectively use differet ISPs

28 Multiple Sessios to a ISP p Several optios ebgp multihop bgp multipath cef loadsharig bgp attribute maipulatio ISP AS

29 Multiple Sessios to a AS ebgp multihop p p p Use ebgp-multihop Ru ebgp betwee loopback addresses ebgp prefixes leared with loopback address as ext hop Cisco IOS router bgp 100 eighbor remote-as 200 eighbor ebgp-multihop 2! ip route serial 1/0 ip route serial 1/1 ip route serial 1/2 Commo error made is to poit remote loopback route at IP address rather tha specific lik AS 200 B A AS 100

30 Multiple Sessios to a AS ebgp multihop p p Oe serious ebgp-multihop caveat: R1 ad R3 are ebgp peers that are loopback peerig eighbor x.x.x.x ebgp-multihop 2 Cofigured with: If the R1 to R3 lik goes dow the sessio could establish via R2 Usually happes whe routig to remote loopback is dyamic, rather tha static poitig at a lik R1 AS 100 R2 Desired Path R3 AS 200 Used Path

31 Multiple Sessios to a ISP ebgp multihop p Try ad avoid use of ebgp-multihop uless: It s absolutely ecessary or Loadsharig across multiple liks p May ISPs discourage its use, for example: We will ru ebgp multihop, but do ot support it as a stadard offerig because customers geerally have a hard time maagig it due to: routig loops failure to realise that BGP sessio stability problems are usually due coectivity problems betwee their CPE ad their BGP speaker 31

32 Multiple Sessios to a AS bgp multi path p p p Three BGP sessios required Platform limit o umber of paths (could be as little as 6) Full BGP feed makes this uwieldy 3 copies of Iteret Routig Table goes ito the FIB AS 200 router bgp 100 eighbor remote-as 200 eighbor remote-as 200 eighbor remote-as 200 maximum-paths 3 AS 100

33 Multiple Sessios to a AS bgp attributes & filters p p p p Simplest scheme is to use defaults Lear/advertise prefixes for better cotrol Plaig ad some work required to achieve loadsharig Poit default towards oe ISP Lear selected prefixes from secod ISP Modify the umber of prefixes leart to achieve acceptable load sharig No magic solutio AS 200 C D A B AS 201

34 Basic Priciples of Multihomig Let s lear to walk before we try ruig 34

35 The Basic Priciples p Aoucig address space attracts traffic (Uless policy i upstream providers iterferes) p Aoucig the ISP aggregate out a lik will result i traffic for that aggregate comig i that lik p Aoucig a subprefix of a aggregate out a lik meas that all traffic for that subprefix will come i that lik, eve if the aggregate is aouced somewhere else The most specific aoucemet wis! 35

36 The Basic Priciples p To split traffic betwee two liks: Aouce the aggregate o both liks - esures redudacy Aouce oe half of the address space o each lik (This is the first step, all thigs beig equal) p Results i: Traffic for first half of address space comes i first lik Traffic for secod half of address space comes i secod lik If either lik fails, the fact that the aggregate is aouced esures there is a backup path 36

37 The Basic Priciples p The keys to successful multihomig cofiguratio: Keepig traffic egieerig prefix aoucemets idepedet of customer ibgp Uderstadig how to aouce aggregates Uderstadig the purpose of aoucig subprefixes of aggregates Uderstadig how to maipulate BGP attributes Too may upstreams/exteral paths makes multihomig harder (2 or 3 is eough!) 37

38 IP Addressig & Multihomig How Good IP Address Plas assist with Multihomig 38

39 IP Addressig & Multihomig p IP Address plaig is a importat part of Multihomig p Previously have discussed separatig: Customer address space Customer p-t-p lik address space Ifrastructure p-t-p lik address space Loopback address space / /24 Customer Address & p-t-p liks Ifrastructure Loopbacks 39

40 IP Addressig & Multihomig p ISP Router loopbacks ad backboe poit to poit liks make up a small part of total address space Ad they do t attract traffic, ulike customer address space p Liks from ISP Aggregatio edge to customer router eeds oe /30 Small requiremets compared with total address space Some ISPs use IP uumbered p Plaig customer assigmets is a very importat part of multihomig Traffic egieerig ivolves subdividig aggregate ito pieces util load balacig works 40

41 Uplaed IP addressig p ISP fills up customer IP addressig from oe ed of the rage: /21 Customer Addresses ISP p Customers geerate traffic Dividig the rage ito two pieces will result i oe /22 with all the customers, ad oe /22 with just the ISP ifrastructure the addresses No loadbalacig as all traffic will come i the first /22 Meas further subdivisio of the first /22 = harder work 41

42 Plaed IP addressig p If ISP fills up customer addressig from both eds of the rage: / Customer Addresses Customer Addresses ISP p Scheme the is: First customer from first /22, secod customer from secod /22, third from first /22, etc p This works also for residetial versus commercial customers: Residetial from first /22 Commercial from secod /22 42

43 Plaed IP Addressig p This works fie for multihomig betwee two upstream liks (same or differet providers) p Ca also subdivide address space to suit more tha two upstreams Follow a similar scheme for populatig each portio of the address space p Do t forget to always aouce a aggregate out of each lik 43

44 Basic Multihomig Let s try some simple worked examples 44

45 Basic Multihomig p No frills multihomig p Will look at two cases: Multihomig with the same ISP Multihomig to differet ISPs p Will keep the examples easy Uderstadig easy cocepts will make the more complex scearios easier to comprehed All assume that the site multihomig has a /19 address block 45

46 Basic Multihomig p This type is most commoplace at the edge of the Iteret Networks here are usually cocered with iboud traffic flows Outboud traffic flows beig earest exit is usually sufficiet p Ca apply to the leaf ISP as well as Eterprise etworks 46

47 Two liks to the same ISP Oe lik primary, the other lik backup oly 47

48 Two liks to the same ISP (oe as backup oly) p Applies whe ed-site has bought a large primary WAN lik to their upstream a small secodary WAN lik as the backup For example, primary path might be a E1, backup might be 64kbps 48

49 Two liks to the same ISP (oe as backup oly) primary C A AS 100 AS E D backup B p AS100 removes private AS ad ay customer subprefixes from Iteret aoucemet 49

50 Two liks to the same ISP (oe as backup oly) p Aouce /19 aggregate o each lik primary lik: p Outboud aouce /19 ualtered p Iboud receive default route backup lik: p Outboud aouce /19 with icreased metric p Iboud received default, ad reduce local preferece p Whe oe lik fails, the aoucemet of the /19 aggregate via the other lik esures cotiued coectivity 50

51 Two liks to the same ISP (oe as backup oly) p Router A Cofiguratio router bgp 65534! etwork mask eighbor remote-as 100 eighbor descriptio RouterC eighbor prefix-list aggregate out eighbor prefix-list default i ip prefix-list aggregate permit /19 ip prefix-list default permit /0! ip route ull0 51

52 Two liks to the same ISP (oe as backup oly) p Router B Cofiguratio router bgp 65534! etwork mask eighbor remote-as 100 eighbor descriptio RouterD eighbor prefix-list aggregate out eighbor route-map routerd-out out eighbor prefix-list default i eighbor route-map routerd-i i..ext slide 52

53 Two liks to the same ISP (oe as backup oly) ip prefix-list aggregate permit /19 ip prefix-list default permit /0! ip route ull0! route-map routerd-out permit 10 set metric 10! route-map routerd-i permit 10 set local-preferece 90! 53

54 Two liks to the same ISP (oe as backup oly) p Router C Cofiguratio (mai lik) router bgp 100! eighbor remote-as eighbor default-origiate eighbor prefix-list Customer i eighbor prefix-list default out ip prefix-list Customer permit /19 ip prefix-list default permit /0 54

55 Two liks to the same ISP (oe as backup oly) p Router D Cofiguratio (backup lik) router bgp 100! eighbor remote-as eighbor default-origiate eighbor prefix-list Customer i eighbor prefix-list default out ip prefix-list Customer permit /19 ip prefix-list default permit /0 55

56 Two liks to the same ISP (oe as backup oly) p Router E Cofiguratio router bgp 100! eighbor remote-as 110 eighbor remove-private-as eighbor prefix-list Customer out ip prefix-list Customer permit /19 p Router E removes the private AS ad customer s subprefixes from exteral aoucemets p Private AS still visible iside AS100 56

57 Two liks to the same ISP With Loadsharig 57

58 Loadsharig to the same ISP p More commo case p Ed sites ted ot to buy circuits ad leave them idle, oly used for backup as i previous example p This example assumes equal capacity circuits Uequal capacity circuits requires more refiemet see later 58

59 Loadsharig to the same ISP Lik oe C A AS 100 AS E D Lik two B p Border router E i AS100 removes private AS ad ay customer subprefixes from Iteret aoucemet 59

60 Loadsharig to the same ISP (with redudacy) p Aouce /19 aggregate o each lik p Split /19 ad aouce as two /20s, oe o each lik basic iboud loadsharig assumes equal circuit capacity ad eve spread of traffic across address block p Vary the split util perfect loadsharig achieved p Accept the default from upstream basic outboud loadsharig by earest exit okay i first approx as most ISP ad ed-site traffic is iboud 60

61 Loadsharig to the same ISP (with redudacy) p Router A Cofiguratio router bgp etwork mask etwork mask eighbor remote-as 100 eighbor prefix-list routerc out eighbor prefix-list default i! ip prefix-list default permit /0 ip prefix-list routerc permit /20 ip prefix-list routerc permit /19! ip route ull0 ip route ull0 61

62 Loadsharig to the same ISP (with redudacy) p Router B Cofiguratio router bgp etwork mask etwork mask eighbor remote-as 100 eighbor prefix-list routerd out eighbor prefix-list default i! ip prefix-list default permit /0 ip prefix-list routerd permit /20 ip prefix-list routerd permit /19! ip route ull0 ip route ull0 62

63 Loadsharig to the same ISP (with redudacy) p Router C Cofiguratio router bgp 100 eighbor remote-as eighbor default-origiate eighbor prefix-list Customer i eighbor prefix-list default out! ip prefix-list Customer permit /19 le 20 ip prefix-list default permit /0 p Router C oly allows i /19 ad /20 prefixes from customer block p Router D cofiguratio is idetical 63

64 Loadsharig to the same ISP (with redudacy) p Router E Cofiguratio router bgp 100! eighbor remote-as 110 eighbor remove-private-as eighbor prefix-list Customer out ip prefix-list Customer permit /19 p Private AS still visible iside AS100 64

65 Loadsharig to the same ISP (with redudacy) p Default route for outboud traffic? Use default-iformatio origiate for the IGP ad rely o IGP metrics for earest exit e.g. o router A: router ospf default-iformatio origiate metric 2 metric-type 1 Or router isis as65534 default-iformatio origiate 65

66 Loadsharig to the same ISP (with redudacy) p Loadsharig cofiguratio is oly o customer router p Upstream ISP has to remove customer subprefixes from exteral aoucemets remove private AS from exteral aoucemets p Could also use BGP commuities 66

67 Two liks to the same ISP Multiple Dualhomed Customers (RFC2270) 67

68 Multiple Dualhomed Customers (RFC2270) p Uusual for a ISP just to have oe dualhomed customer Valid/valuable service offerig for a ISP with multiple PoPs Better for ISP tha havig customer multihome with aother provider! p Look at scalig the cofiguratio Þ Simplifyig the cofiguratio Usig templates, peer-groups, etc Every customer has the same cofiguratio (basically) 68

69 Multiple Dualhomed Customers (RFC2270) AS 100 C A1 B1 AS E D A2 AS B2 p A3 AS Border router E i AS100 removes private AS ad ay customer B3 subprefixes from Iteret aoucemet 69

70 Multiple Dualhomed Customers (RFC2270) p Customer aoucemets as per previous example p Use the same private AS for each customer documeted i RFC2270 address space is ot overlappig each customer hears default oly p Router A ad B cofiguratio same as Router A ad B previously 70

71 Multiple Dualhomed Customers (RFC2270) p Router A1 Cofiguratio router bgp etwork mask etwork mask eighbor remote-as 100 eighbor prefix-list routerc out eighbor prefix-list default i! ip prefix-list default permit /0 ip prefix-list routerc permit /20 ip prefix-list routerc permit /19! ip route ull0 ip route ull0 71

72 Multiple Dualhomed Customers (RFC2270) p Router B1 Cofiguratio router bgp etwork mask etwork mask eighbor remote-as 100 eighbor prefix-list routerd out eighbor prefix-list default i! ip prefix-list default permit /0 ip prefix-list routerd permit /20 ip prefix-list routerd permit /19! ip route ull0 ip route ull0 72

73 Multiple Dualhomed Customers (RFC2270) p Router C Cofiguratio router bgp 100 eighbor bgp-customers peer-group eighbor bgp-customers remote-as eighbor bgp-customers default-origiate eighbor bgp-customers prefix-list default out eighbor peer-group bgp-customers eighbor descriptio Customer Oe eighbor prefix-list Customer1 i eighbor peer-group bgp-customers eighbor descriptio Customer Two eighbor prefix-list Customer2 i 73

74 Multiple Dualhomed Customers (RFC2270) eighbor peer-group bgp-customers eighbor descriptio Customer Three eighbor prefix-list Customer3 i! ip prefix-list Customer1 permit /19 le 20 ip prefix-list Customer2 permit /19 le 20 ip prefix-list Customer3 permit /19 le 20 ip prefix-list default permit /0 p Router C oly allows i /19 ad /20 prefixes from customer block 74

75 Multiple Dualhomed Customers (RFC2270) p Router D Cofiguratio router bgp 100 eighbor bgp-customers peer-group eighbor bgp-customers remote-as eighbor bgp-customers default-origiate eighbor bgp-customers prefix-list default out eighbor peer-group bgp-customers eighbor descriptio Customer Oe eighbor prefix-list Customer1 i eighbor peer-group bgp-customers eighbor descriptio Customer Two eighbor prefix-list Customer2 i 75

76 Multiple Dualhomed Customers (RFC2270) eighbor peer-group bgp-customers eighbor descriptio Customer Three eighbor prefix-list Customer3 i! ip prefix-list Customer1 permit /19 le 20 ip prefix-list Customer2 permit /19 le 20 ip prefix-list Customer3 permit /19 le 20 ip prefix-list default permit /0 p Router D oly allows i /19 ad /20 prefixes from customer block 76

77 Multiple Dualhomed Customers (RFC2270) p Router E Cofiguratio assumes customer address space is ot part of upstream s address block router bgp 100! eighbor remote-as 110 eighbor remove-private-as eighbor prefix-list Customers out ip prefix-list Customers permit /19 ip prefix-list Customers permit /19 ip prefix-list Customers permit /19 p Private AS still visible iside AS100 77

78 Multiple Dualhomed Customers (RFC2270) p If customers prefixes come from ISP s address block do NOT aouce them to the Iteret aouce ISP aggregate oly p Router E cofiguratio: router bgp 100 eighbor remote-as 110 eighbor prefix-list my-aggregate out! ip prefix-list my-aggregate permit /13 78

79 Multihomig Summary p Use private AS for multihomig to the same upstream p Leak subprefixes to upstream oly to aid loadsharig p Upstream router E cofiguratio is idetical across all situatios 79

80 Basic Multihomig Multihomig to Differet ISPs 80

81 Two liks to differet ISPs p Use a Public AS Or use private AS if agreed with the other ISP But some people do t like the icosistet- AS which results from use of a private-as p Address space comes from both upstreams or Regioal Iteret Registry p Cofiguratio cocepts very similar 81

82 Icosistet-AS? p Viewig the prefixes origiated by AS65534 i the Iteret shows they appear to be origiated by both AS210 ad AS200 This is NOT bad Nor is it illegal p IOS commad is show ip bgp icosistet-as AS AS 200 AS 210 Iteret 82

83 Two liks to differet ISPs Oe lik primary, the other lik backup oly 83

84 Two liks to differet ISPs (oe as backup oly) Iteret AS 100 AS 120 C D Aouce /19 block A B Aouce /19 block with loger AS PATH AS

85 Two liks to differet ISPs (oe as backup oly) p Aouce /19 aggregate o each lik primary lik makes stadard aoucemet backup lik legthes the AS PATH by usig AS PATH preped p Whe oe lik fails, the aoucemet of the /19 aggregate via the other lik esures cotiued coectivity 85

86 Two liks to differet ISPs (oe as backup oly) p Router A Cofiguratio router bgp 130! etwork mask eighbor remote-as 100 eighbor prefix-list aggregate out eighbor prefix-list default i ip prefix-list aggregate permit /19 ip prefix-list default permit /0! ip route ull0 86

87 Two liks to differet ISPs (oe as backup oly) p Router B Cofiguratio router bgp 130 etwork mask eighbor remote-as 120 eighbor prefix-list aggregate out eighbor route-map routerd-out out eighbor prefix-list default i eighbor route-map routerd-i i! ip prefix-list aggregate permit /19 ip prefix-list default permit /0! route-map routerd-out permit 10 set as-path preped ! route-map routerd-i permit 10 set local-preferece 80 87

88 Two liks to differet ISPs (oe as backup oly) p Not a commo situatio as most sites ted to prefer usig whatever capacity they have (Useful whe two competig ISPs agree to provide mutual backup to each other) p But it shows the basic cocepts of usig local-prefs ad AS-path prepeds for egieerig traffic i the chose directio 88

89 Two liks to differet ISPs With Loadsharig 89

90 Two liks to differet ISPs (with loadsharig) Iteret AS 100 AS 120 C D Aouce first /20 ad /19 block A B Aouce secod /20 ad /19 block AS

91 Two liks to differet ISPs (with loadsharig) p Aouce /19 aggregate o each lik p Split /19 ad aouce as two /20s, oe o each lik basic iboud loadsharig p Whe oe lik fails, the aoucemet of the /19 aggregate via the other ISP esures cotiued coectivity 91

92 Two liks to differet ISPs (with loadsharig) p Router A Cofiguratio router bgp 130! etwork mask etwork mask eighbor remote-as 100 eighbor prefix-list firstblock out eighbor prefix-list default i ip prefix-list default permit /0! ip prefix-list firstblock permit /20 ip prefix-list firstblock permit /19 92

93 Two liks to differet ISPs (with loadsharig) p Router B Cofiguratio router bgp 130! etwork mask etwork mask eighbor remote-as 120 eighbor prefix-list secodblock out eighbor prefix-list default i ip prefix-list default permit /0! ip prefix-list secodblock permit /20 ip prefix-list secodblock permit /19 93

94 Two liks to differet ISPs (with loadsharig) p Loadsharig i this case is very basic p But shows the first steps i desigig a load sharig solutio Start with a simple cocept Ad build o it! 94

95 Two liks to differet ISPs More Cotrolled Loadsharig 95

96 Loadsharig with differet ISPs Iteret AS 100 AS 120 C D Aouce /19 block A B Aouce /20 subprefix, ad /19 block with loger AS path AS

97 Loadsharig with differet ISPs p Aouce /19 aggregate o each lik O first lik, aouce /19 as ormal O secod lik, aouce /19 with loger AS PATH, ad aouce oe /20 subprefix p cotrols loadsharig betwee upstreams ad the Iteret p Vary the subprefix size ad AS PATH legth util perfect loadsharig achieved p Still require redudacy! 97

98 Loadsharig with differet ISPs p Router A Cofiguratio router bgp 130! etwork mask eighbor remote-as 100 eighbor prefix-list default i eighbor prefix-list aggregate out ip prefix-list aggregate permit /19 ip prefix-list default permit /0! ip route ull0 98

99 Loadsharig with differet ISPs p Router B Cofiguratio router bgp 130 etwork mask etwork mask eighbor remote-as 120 eighbor prefix-list default i eighbor prefix-list subblocks out eighbor route-map routerd out! route-map routerd permit 10 match ip address prefix-list aggregate set as-path preped route-map routerd permit 20! ip prefix-list subblocks permit /19 le 20 ip prefix-list aggregate permit /19 99

100 Loadsharig with differet ISPs p This example is more commoplace p Shows how ISPs ad ed-sites subdivide address space frugally, as well as use the AS-PATH preped cocept to optimise the load sharig betwee differet ISPs p Notice that the /19 aggregate block is ALWAYS aouced 100

101 Summary 101

102 Summary p Previous examples dealt with simple case p Load balacig iboud traffic flow Achieved by modifyig outboud routig aoucemets Aggregate is always aouced p We have ot looked at outboud traffic flow For ow this is left as earest exit 102

103 Simple Multihomig ISP Traiig Workshops 103