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BGP Diverse Paths. draft -ietf-grow-diverse-bgp-paths-dist-02. Keyur Patel. RIPE 61 , November 2010, Rome, Italy. Motivation. BGP protocol defined in RFC4271 provides a mechanism to announce only a single path aka a BGP bestpath

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Bgp diverse paths

BGP Diverse Paths

draft-ietf-grow-diverse-bgp-paths-dist-02

  • KeyurPatel

  • RIPE 61, November 2010, Rome, Italy


Motivation

Motivation

  • BGP protocol defined in RFC4271 provides a mechanism to announce only a single path aka a BGP bestpath

  • Announcement of multiple paths within BGP is gradually becoming a requirement

    • Used for BGP Fast Convergence

  • Different solutions available to announce multiple paths with BGP

    • BGP Full mesh + BGP Best External

    • BGP Additional Paths

    • Different RD approach in BGP VPNs

    • BGP Diverse paths


Bgp full mesh bgp best external

BGP Full Mesh + BGP Best External

  • BGP full mesh explained at length in BGP RFC 4271

    • Assures path diversity in hot potato routing

    • Needs BGP Best External support for cold potato routing

  • BGP Best External explained at length in draft-ietf-idr-best-external-02.txt

  • All BGP speaking routers establish peering with each other

    • Results in TCP state explosion

    • BGP can store as many paths as sessions


Bgp add paths

BGP Add Paths

  • BGP Add paths explained at length in draft-walton-bgp-addpaths-06.txt

  • Mechanism to announce multiple paths over a single neighbor session

  • New BGP protocol encoding and a capability

    • Requires a network-wide upgrade

  • Operators need to figure out how many paths and what paths to announce

    • Can the edge router handle a load of more than 2 paths?


Vpns different rd approach

VPNs & Different RD Approach

  • L3VPNs can announce multiple paths using different RD approach

    • Implementation tweak: - SPs can configure multiple RDs for their multi-homed customers

    • Each unique RD creates separate set of customer prefixes and thereby ensures multiple paths

  • Works well and deployed in most of the L3VPN environment

    • No reason to look into BGP Add Paths or BGP Diverse paths


Bgp diverse paths1

BGP Diverse Paths

  • RR based solution

    • Does NOT require an upgrade of an entire network

  • Does not require any protocol changes

  • Applicable to all BGP AFI/SAFIs

    • Targeted mostly for IP hop-by-hop as well as tunneled networks

  • Diverse paths are announced either using

    • Shadow RRs that calculate only diverse paths

    • Shadow sessions that announce only diverse paths


Bgp diverse paths rr f unctionality

BGP Diverse Paths (RR Functionality)

  • RRs need to pre-compute diverse paths as part of its bestpath processing

  • RR can operate as if it was a diverse/backup RR and only announce diverse paths to its configured neighbors

    • IGP metric check needs to be disabled in order to deterministically compute diverse paths

  • Alternatively RRs can track session types and announce appropriate diverse path accordingly

    • Requires configuration of new addresses for diverse path sessions (one address per nth diverse path announced to all BGP neighbors)

  • RRs in forwarding plane needs to pre-compute and install diverse paths in its RIB and FIB

    • Covers hot potato routing as well as cold potato routing

  • RR needs to account for additional diverse path computation


Diverse paths pe asbr functionality

Diverse Paths PE/ASBR Functionality

  • PE/ASBR may need configure additional sessions with RRs

    • Does NOT require any software upgrade

    • Can reuse its existing peering address for diverse path sessions

  • PE/ASBR treats diverse paths as just another BGP path received

  • PE/ASBR can use diverse paths to pre-compute and install backup paths in RIB and FIB

  • PE/ASBR needs to account for

    • Additional sessions to enable diverse paths

    • Additional memory to store diverse paths


Rr deployment models

RR Deployment Models

Today’s case:

Diverse sessions:

Diverse RR:

10/8 - P1*, P2 ....

10/8 - P1*, P2 ....

10/8 - P1*, P2 ....

RR1

RR2

RR1

RR2

RR1

RR2

s1

s2

PE/ASBR

PE/ASBR

PE/ASBR

10/8 - P1 via RR1

- P1 via RR2

10/8 - P1 via RR1

- P2 via RR2

10/8 - P1 via RR1

- P1 via RR2 s1

- P2 via RR2 s2

RR1 & RR2 same IGP location or IGP metric ignore in best path

Possible to peer both sessions s1 and s2 to the same loopback on PE/ASBR.


Ibgp network w ith f lat i gp m ultiple rr clusters

IBGP Network With Flat Igp & Multiple RR Clusters

P1/nh ASBR1

PE4

P1

RR1

P1/nh ASBR1

P2

ASBR2

P1

P1, P2, P3a, P3b

ASBR1

RR2

PE2

P1/nh ASBR1

PE1

P1/nh ASBR1

P1/nh ASBR1

P1/nh ASBR1

ASBR3a

ASBR3b

P3a

P3b


Ibgp network w ith f lat i gp multiple rr shadow rr clusters

IBGP Network With Flat Igp, Multiple RR & Shadow RR Clusters

P2/nh ASBR2

P1/nh ASBR1

PE4

  • RR1’ and RR2’ are shadow RRs

  • RR1, RR1’ & RR2, RR2’ are in different

  • clusters

  • They are configured to calculate and

  • advertisediverse path to it’s clients

  • They can do it on a per AFI/SAFI basis

  • Same IGP metric as best RRs or IGP metric

  • disabled on both

  • P1 overall best and P2 second best/diverse

P1

RR1

P1/nh ASBR1

P2

P1, P2

ASBR2

RR1’

P2/nh ASBR2

P1

P1, P2, P3a, P3b

ASBR1

RR2

PE2

  • Deployment Considerations:

  • No upgrade of any existing PE/ASBR is

  • required

  • Additional IBGP session per eachdiverse

  • path

  • Additional shadow RR per cluster

  • Works within flat domain or within each

  • area of hierarchical network

P2, P3a, P3b

P1/nh ASBR1

RR2’

P2/nh ASBR2

PE1

P1/nh ASBR1

P2/nh ASBR2

P1/nh ASBR1

P1/nh ASBR1

ASBR3a

ASBR3b

P2/nh ASBR2

P2/nh ASBR2

P3a

P3b


Ibgp network with f lat i gp a nd m ultiple rr clusters

IBGP Network With Flat Igp And Multiple RR Clusters

P1/nh ASBR1

P2/nh ASBR2

PE4

  • RRs and RRs’ are same RRs

  • RR1, RR1’ & RR2, RR2’ are in different

  • clusters

  • They are configured to calculate and

  • advertisediversepath to it’s clients on a

  • per neighbor basis

  • They can do it on a per AFI/SAFI basis

  • Same IGP metric as best RRs

  • P1 overall best, P2 second best/diverse

RR1

P1, P2

P1/nh ASBR1

RR1’

P2

ASBR2

P2/nh ASBR2

P1

ASBR1

P1, P2, P3a, P3b

RR2

PE2

RR2’

P1/nh ASBR1

P2/nh ASBR2

PE1

P1/nh ASBR1

P2/nh ASBR2

  • Deployment Considerations:

  • No upgrade of any existing PE/ASBR is

  • required

  • Additional IBGP sessions per each diverse

  • path

  • No additional Shadow RRs required

  • Works within flat domain or within each

  • area of hierarchical network

P1/nh ASBR1

P1/nh ASBR1

ASBR3a

ASBR3b

P2/nh ASBR2

P2/nh ASBR2

P3a

P3b


Hierarchial rrs

Hierarchial RRs

PE4

  • Each shadow RR is configured to

  • calculate andadvertise diverse path

  • to it’s clients (POP RRs) on a

  • per neighbor basis

  • They can do it on a per AFI/SAFI basis

  • Any encapsulation can be used

  • within each area IP or MPLS (option).

  • Pop RRs replicate the design in the

  • same manner

RR4a

RR4b

P1

P2

P3

P1

P2

P3

P2

ASBR2

P1

ASBR1

P1 P2 P3

L2-RR1

RR1a

RR2a

P1 P2 P3

P1

P2

P3

P1

P2

P3

L2-RR1’

P1 P2 P3

L2-RR1”

RR1b

RR2b

PE1

P1

P2

P3

P1

P2

P3

PE2

P1

P2

P3

P1

P2

P3

RR3a

RR3b

P3a

P3b

P3a

P3b

  • Deployment Consideration:

  • No upgrade of any existing PE/ASBR is

  • required

  • Additional IBGP sessions per each

  • diverse path

ASBR3a

ASBR3b

P3a

P3b


Diverse paths bgp best external

Diverse Paths & BGP Best External

  • Intra-cluster routes may not always get announced with diverse paths

    • Diverse paths does NOT change any BGP route propagation rules

    • IBGP network still has multiple diverse paths for a given prefix

    • Not an issue within a Cluster

  • Usage of BGP Best External between RRs can assure announcements of intra cluster routes

    • Reduce number of sessions between full meshed RRs

    • Achieve higher path diversity within the network


Diverse paths with missing intra cluster routes

Diverse Paths With Missing Intra-Cluster routes

P3a/nh ASBR3a

P3b/nh ASBR3b

PE4

  • RRs and RRs’ are same RRs

  • RR1, RR1’ & RR2, RR2’ are in different

  • clusters

  • They are configured to calculate and

  • advertisediversepath to it’s clients on a

  • per neighbor basis

  • They can do it on a per AFI/SAFI basis

  • Same IGP metric as best RRs

  • Cold Potato Routing (Local Prefs win)

  • P3a overall best, P3b second best/diverse

  • RR1 and RR1’ got 3 paths

  • RR2 and RR2’ got 3 paths

  • Network still has path diversity

P3a/nh ASBR3a

RR1

P3a, P3b, P1,

P3b/nh ASBR3b

RR1’

P2

ASBR2

P3a/nh ASBR3a

P3b/nh ASBR3b

P1

ASBR1

RR2

P3a, P3b, P2

PE2

RR2’

P3a/nh ASBR3a

P3b/nh ASBR3b

PE1

P3a/nh ASBR3a

P3b/nh ASBR3b

ASBR3a

ASBR3b

P3b/nh ASBR3b

P3a/nh ASBR3a

P3a

P3b


Bgp diverse paths bgp best external

BGP Diverse Paths + BGP Best External

P3a/nh ASBR3a

P3b/nh ASBR3b

PE4

  • RRs and RRs’ are same RRs

  • RR1, RR1’ & RR2, RR2’ are in different

  • clusters

  • They are configured to calculate and

  • advertisediversepath to it’s clients on a

  • per neighbor basis

  • They can do it on a per AFI/SAFI basis

  • Same IGP metric as best RRs

  • Cold Potato Routing (Local Prefs win)

  • P3a overall best, P3b second best/diverse

  • RR1 and RR1’ got 3 paths

  • RR2 and RR2’ got 4 paths

  • Network still has path diversity

P3a/nh ASBR3a

RR1

P3a, P3b, P1

P3b/nh ASBR3b

RR1’

P2

ASBR2

P3a/nh ASBR3a

P3b/nh ASBR3b

P1

ASBR1

P3a, P3b, P1, P2

RR2

PE2

RR2’

P3a/nh ASBR3a

P3b/nh ASBR3b

PE1

P3a/nh ASBR3a

P3b/nh ASBR3b

ASBR3a

ASBR3b

P3b/nh ASBR3b

P3a/nh ASBR3a

P3a

P3b


Bgp diverse paths bgp best external1

BGP Diverse Paths + BGP Best External

P3a/nh ASBR3a

P1/nh ASBR1

PE4

  • RRs and RRs’ are same RRs

  • RR1, RR1’ & RR2, RR2’ are in different

  • clusters

  • They are configured to calculate and

  • advertisediversepath to it’s clients on a

  • per neighbor basis

  • No diverse session between RRs

  • Best External enabled between RRs

  • They can do it on a per AFI/SAFI basis

  • Same IGP metric as best RRs

  • P3a overall best, P1 & P3b second best/

  • diverse

  • RR1 and RR1’ got 2 paths

  • RR2 and RR2’ got 4 paths

  • Network still has path diversity

  • Single session between RRs

P3a/nh ASBR3a

RR1

P3a, P1

P3b/nh ASBR3b

RR1’

P2

ASBR2

P3a/nh ASBR3a

P1

ASBR1

P3a, P3b, P1, P2

RR2

PE2

RR2’

P3a/nh ASBR3a

P3b/nh ASBR3b

PE1

P3a/nh ASBR3a

P1/nh ASBR1

ASBR3a

ASBR3b

P3b/nh ASBR3b

P3a/nh ASBR3a

P3a

P3b


Acknowledgements

Acknowledgements

Special Thanks to:

Randy Bush

Robert Raszuk

Chris Cassar

SatishMynam

Selma Yilmaz


Questions

Questions?


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