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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

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