Transitioning to BGP

Transcription

1 Trasitioig to BGP ISP Workshops These materials are licesed uder the Creative Commos Attributio-NoCommercial 4.0 Iteratioal licese ( Last updated 24 th April

2 Ackowledgemets p This material origiated from the Cisco ISP/IXP Workshop Programme developed by Philip Smith & Barry Greee p Use of these materials is ecouraged as log as the source is fully ackowledged ad this otice remais i place p Bug fixes ad improvemets are welcomed Please workshop (at) bgp4all.com Philip Smith 2

3 Scalig the etwork How to get out of carryig all prefixes i IGP 3

4 Why use BGP rather tha IGP? p IGP has Limitatios: The more routig iformatio i the etwork p Periodic updates/floodig overload p Log covergece times p Affects the core first Policy defiitio p Not easy to do 4

5 Preparig the Network p We wat to deploy BGP ow p Because BGP will be used a ASN is required p If ot multihomig, a private ASN is sufficiet p If multihomig to differet ISPs is iteded i the ear future, a public ASN should be obtaied: Either go to upstream ISP who is a registry member or Apply to the RIR yourself for a oe off assigmet or Ask a ISP who is a registry member or Joi the RIR ad get your ow IP address allocatio too (this optio strogly recommeded) 5

6 Preparig the Network p Will look at two examples of BGP deploymet: Example Oe: etwork uses oly static routes Example Two: etwork is curretly ruig a IGP

7 Preparig the Network Example Oe p The etwork is ot ruig ay BGP at the momet sigle statically routed coectio to upstream ISP p The etwork is ot ruig ay IGP at all Static default ad routes through the etwork to do routig 7

8 Preparig the Network First Step: IGP p Decide o a IGP: OSPF or IS-IS J See the ISIS vs OSPF presetatio p Assig loopback iterfaces ad /32 address to each router which will ru the IGP Loopback is used for OSPF ad BGP router id achor Used for ibgp ad route origiatio p Deploy IGP (e.g. OSPF) IGP ca be deployed with NO IMPACT o the existig static routig e.g. OSPF distace might be 110; static distace is 1 Smallest distace wis 8

9 Preparig the Network IGP (cot) p Be prudet deployig IGP keep the Lik State Database Lea Router loopbacks go i IGP WAN poit to poit liks go i IGP (I fact, ay lik where IGP dyamic routig will be ru should go ito IGP) Summarise o area/level boudaries (if possible) i.e. thik about your IGP address pla 9

10 Preparig the Network IGP (cot) p Routes which do t go ito the IGP iclude: Dyamic assigmet pools (DSL/Cable/Dial) Customer poit to poit lik addressig p (usig ext-hop-self i ibgp esures that these do NOT eed to be i IGP) Static/Hostig LANs Customer assiged address space Aythig else ot listed i the previous slide 10

11 Preparig the Network OSPF iterface loopback 0 ip address ip ospf 100 area 0 iterface Etheret 0/0 ip address ip ospf 100 area 0 iterface serial 0/0 ip address iterface serial 0/1 ip address router ospf 100 passive-iterface default o passive-iterface Etheret 0/0 ip route serial 0/0 ip route serial 0/1 Add loopback cofiguratio Customer coectios

12 Preparig the Network Secod Step: ibgp p p p Secod step is to cofigure the local etwork to use ibgp ibgp ca ru o all routers, or a subset of routers, or just o the upstream edge ibgp must ru o all routers which are i the trasit path betwee exteral coectios A F B D E AS200 C 12

13 Preparig the Network Secod Step: ibgp (Trasit Path) p p p ibgp must ru o all routers which are i the trasit path betwee exteral coectios Routers C, E ad F are ot i the trasit path Static routes or IGP will suffice Router D is i the trasit path Will eed to be i ibgp mesh, otherwise routig loops will result A F B D E AS200 C 13

14 Preparig the Network Layers p Typical SP etworks have three layers: Core the backboe, usually the trasit path Distributio the middle, PoP aggregatio layer Aggregatio the edge, the devices coectig customers 14

15 Preparig the Network Aggregatio Layer p ibgp is optioal May ISPs ru ibgp here, either partial routig (more commo) or full routig (less commo) Full routig is ot eeded uless customers wat full table Partial routig is cheaper/easier, might usually cosist of iteral prefixes ad, optioally, exteral prefixes to aid exteral load balacig p Commuities ad peer-groups make this admiistratively easy p May aggregatio devices ca t ru ibgp Static routes from distributio devices for address pools IGP for best exit 15

16 Preparig the Network Distributio Layer p Usually rus ibgp Partial or full routig (as with aggregatio layer) p But does ot have to ru ibgp IGP is the used to carry customer prefixes (does ot scale) IGP is used to determie earest exit p Networks which pla to grow large should deploy ibgp from day oe Migratio at a later date is extra work No extra overhead i deployig ibgp, ideed IGP beefits 16

17 Preparig the Network Core Layer p Core of etwork is usually the trasit path p ibgp ecessary betwee core devices Full routes or partial routes: p Trasit ISPs carry full routes i core p Edge ISPs carry partial routes oly p Core layer icludes AS border routers 17

18 Preparig the Network ibgp Implemetatio p Decide o: Best ibgp policy p Will it be full routes everywhere, or partial, or some mix? ibgp scalig techique p Commuity policy? p Route-reflectors? p Techiques such as peer groups ad peer templates? 18

19 Preparig the Network ibgp Implemetatio p The deploy ibgp: Step 1: Itroduce ibgp mesh o chose routers p make sure that ibgp distace is greater tha IGP distace (it usually is) Step 2: Istall customer prefixes ito ibgp Check Does the etwork still work? Step 3: Carefully remove the static routig for the prefixes ow i IGP ad ibgp Check Does the etwork still work? Step 4: Deploymet of ebgp follows 19

20 Preparig the Network ibgp Implemetatio Istall customer prefixes ito ibgp? p Customer assiged address space Network statemet/static route combiatio Use uique commuity to idetify customer assigmets p Customer facig poit-to-poit liks Redistribute coected through filters which oly permit poit-to-poit lik addresses to eter ibgp Use a uique commuity to idetify poit-to-poit lik addresses (these are oly required for your moitorig system) p Dyamic assigmet pools & local LANs Simple etwork statemet will do this Use uique commuity to idetify these etworks 20

21 Preparig the Network ibgp Implemetatio Carefully remove static routes? p Work o oe router at a time: Check that static route for a particular destiatio is also leared by the ibgp If so, remove it If ot, establish why ad fix the problem (Remember to look i the RIB, ot the FIB) p The the ext router, util the whole PoP is doe p The the ext PoP, ad so o util the etwork is ow depedet o the IGP ad ibgp you have deployed 21

22 Preparig the Network Completio p Previous steps are NOT flag day steps Each ca be carried out durig differet maiteace periods, for example: Step Oe o Week Oe Step Two o Week Two Step Three o Week Three Ad so o Ad with proper plaig will have NO customer visible impact at all 22

23 Preparig the Network Cofiguratio Before BGP iterface loopback 0 ip address ip ospf 100 area 0 iterface etheret 0/0 ISP backboe ip address ip ospf 100 area 0 iterface serial 0/0 Customer ip address router ospf 100 passive-iterface default o passive-iterface etheret 0/0 ip route serial 0/0 Add loopback cofiguratio if ot already there 23

24 Preparig the Network Cofiguratio Steps 1 & 2 iterface ad OSPF cofiguratio uchaged router bgp 100 redistribute coected subets route-map poit-to-poit eighbor remote-as 100 eighbor ext-hop-self... etwork mask distace bgp ip route serial 0/0 route-map poit-to-poit permit 5 match ip address 1 set commuity 100:1 access-list 1 permit Add BGP ad related cofiguratio i red 24

25 Preparig the Network Example Two p The etwork is ot ruig ay BGP at the momet sigle statically routed coectio to upstream ISP p The etwork is ruig a IGP though All iteral routig iformatio is i the IGP By IGP, OSPF or ISIS is assumed

26 Preparig the Network IGP p If ot already doe, assig loopback iterfaces (with /32 addresses) to each router which is ruig the IGP Loopback is used for OSPF ad BGP router id achor Used for ibgp ad route origiatio p Esure that the loopback /32s are appearig i the IGP

27 Preparig the Network ibgp p Go through the ibgp decisio process as i Example Oe p Decide full or partial, ad the extet of the ibgp reach i the etwork

28 Preparig the Network ibgp Implemetatio p The deploy ibgp: Step 1: Itroduce ibgp mesh o chose routers p make sure that ibgp distace is greater tha IGP distace (it usually is) Step 2: Istall customer prefixes ito ibgp Check Does the etwork still work? Step 3: Reduce BGP distace to be less tha the IGP p (so that ibgp routes take priority) Step 4: Carefully remove the customer prefixes from the IGP Check Does the etwork still work? Step 5: Restore BGP distace to be greater tha IGP Step 6: Deploymet of ebgp follows

29 Preparig the Network ibgp Implemetatio Istall customer prefixes ito ibgp? p Customer assiged address space Network statemet/static route combiatio Use uique commuity to idetify customer assigmets p Customer facig poit-to-poit liks Redistribute coected through filters which oly permit poit-to-poit lik addresses to eter ibgp Use a uique commuity to idetify poit-to-poit lik addresses (these are oly required for your moitorig system) p Dyamic assigmet pools & local LANs Simple etwork statemet will do this Use uique commuity to idetify these etworks

30 Preparig the Network ibgp Implemetatio Carefully remove customer routes from IGP? p Work o oe router at a time: Check that IGP route for a particular destiatio is also leared by ibgp If so, remove it from the IGP If ot, establish why ad fix the problem (Remember to look i the RIB, ot the FIB) p The the ext router, util the whole PoP is doe p The the ext PoP, ad so o util the etwork is ow depedet o the ibgp you have deployed

31 Preparig the Network Example Two Cofiguratio Before BGP iterface loopback 0 ip address ip ospf 100 area 0 iterface serial 0/0 ip address iterface serial 0/1 ip address router ospf 100 passive-iterface loopback 0 redistribute coected subets redistribute static subets ip route serial 0/0 ip route serial 0/1 Add loopback cofiguratio if ot already there Poit-to-poit liks Customer etworks

32 Preparig the Network Example Two Cofiguratio Steps 1 & 2 iterface ad OSPF cofiguratio uchaged router bgp 100 redistribute coected subets route-map poit-to-poit eighbor remote-as 100 eighbor ext-hop-self... etwork mask etwork mask distace bgp ip route serial 0/0 ip route serial 0/1 route-map poit-to-poit permit 5 match ip address 1 set commuity 100:1 access-list 1 permit Add BGP ad related cofiguratio i red

33 Preparig the Network Example Two Cofiguratio Steps 3 & 4 router ospf 100 passive-iterface default o passive-iterface etheret 0/0 router bgp 100 redistribute coected route-map poit-to-poit eighbor remote-as 100 eighbor ext-hop-self... etwork mask etwork mask distace bgp ip route serial 0/0 ip route serial 0/1...etc... reduced BGP distace OSPF redistributio has bee removed, OSPF tidied up

34 Preparig the Network Example Two Cofiguratio Step 5 router ospf 100 passive-iterface default o passive-iterface etheret 0/0 router bgp 100 redistribute coected route-map poit-to-poit eighbor remote-as 100 eighbor ext-hop-self... etwork mask etwork mask distace bgp BGP distace restored ip route serial 0/0 ip route serial 0/1...etc...

35 Preparig the Network Completio p Previous steps are NOT flag day steps Each ca be carried out durig differet maiteace periods, for example: Step Oe o Week Oe Step Two o Week Two Step Three o Week Three Ad so o Ad with proper plaig will have NO customer visible impact at all

36 Preparig the Network Cofiguratio Summary p IGP essetial etworks are i IGP p Customer etworks are ow i ibgp ibgp deployed over the backboe Full or Partial or Upstream Edge oly p BGP distace is greater tha ay IGP p Now ready to deploy ebgp

37 Trasitioig to BGP ISP Workshops 37