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An analysis of scaling issues in MPLS-TE backbone networks

An analysis of scaling issues in MPLS-TE backbone networks. Seisho Yasukawa, Adrian Farrel, and Olufemi Komolafe draft-yasukawa-mpls-scaling-analysis-04.txt. Introduction. Motivated by concerns about potentially excessive number of LSPs in MPLS-TE networks PE-PE LSPs required in a full mesh

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An analysis of scaling issues in MPLS-TE backbone networks

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  1. An analysis of scaling issues in MPLS-TE backbone networks Seisho Yasukawa, Adrian Farrel, and Olufemi Komolafe draft-yasukawa-mpls-scaling-analysis-04.txt 69th IETF Chicago July 2007

  2. Introduction • Motivated by concerns about potentially excessive number of LSPs in MPLS-TE networks • PE-PE LSPs required in a full mesh • Multiple ‘parallel’ LSPs for service differentiation • How many LSPs can a core P-node support? • The old n-squared problem re-surfaces • Simple math…1000 PEs means up to 999000 LSPs in the core (per service type) • Important issue because number of LSPs supported by LSR constrained by factors such as • Amount of LSP state • Processing overhead • RSVP-TE overhead • Management complexity • Open questions include • Does use of hierarchical LSPs solve problem? • Are there other solutions? 69th IETF Chicago July 2007

  3. Progress • Last discussed in Dallas (March 2006) • Updates • Added discussion of “ladder topology” • New author: Femi from Glasgow University • Checked (and corrected) the math • Revised to clarify the problem and objectives 69th IETF Chicago July 2007

  4. Approach • Use exemplar topologies to give insight into potential MPLS-TE scaling issues • Exemplar topologies • Have characteristics similar to real networks • e.g. tree-like at edges, mesh-like in core • Have well-defined connectivity and symmetry • Amenable to mathematical analysis • Exemplar topologies considered in draft • Snowflake topology • Ladder network topology 69th IETF Chicago July 2007

  5. Exemplar Snowflake Network • Meshed core of P(1) nodes • P(n+1) nodes connected to P(n) nodes • PE nodes connected to P nodes • Well-defined connectivity and symmetry allows many important metrics to be computed • Number of levels & number of nodes per level may be varied PE P(2) P(1) 69th IETF Chicago July 2007

  6. Exemplar Ladder Network • Core of P(1) nodes looks like a ladder • Symmetrical trees subtended to core • P(n+1) nodes connected to P(n) nodes • PE nodes connected to P nodes • Well-defined connectivity and symmetry allows many important metrics to be computed • Number of levels & number of nodes per level may be varied P(1) P(2) PE 69th IETF Chicago July 2007

  7. Method • Using Snowflake & Ladder network, can study MPLS-TE scaling, considering • Flat networks • Forwarding adjacencies (hierarchical LSPs) • MP2P LSPs • Interesting metrics include • Number of PEs • Number of LSPs traversing different LSRs • Amount of LSP state at any LSR • Ratio of PE to P LSRs (cost-effectiveness) 69th IETF Chicago July 2007

  8. What are the Scaling Limitations? • Number of labels on a link • Signaling state on an LSR • Simple constraint on memory usage • Signaling processing • Searching control blocks • RSVP-TE soft state (even with refresh reduction) • RSVP-TE Hellos • Management • How many LSPs can the EMS/NMS handle • Monitoring • What management protocol load can the network support? • Status and statistics 69th IETF Chicago July 2007

  9. Normal Suggestion - Hierarchy • Hierarchical LSPs scale well, but: • Not as well as you might think • Obviously no benefit from core tunnels • PE-PE tunnels don’t help n-squared problem • Multiple layers of hierarchy needed to make full impact • Tunnel end-points see increase in state • Adds a significant management overhead • All tunnel end-points have to be planned • All tunnels have to be provisioned • Auto-mesh can help • Other issues: • OAM for PE-PE LSPs is degraded • Loss of information inside the tunnel • LSP aggregation reduces PE-PE TE possibilities • TE bandwidth granularity is reduced 69th IETF Chicago July 2007

  10. A Scaling Alternative – MP2P LSPs • LSPs “merge” automatically • Reduces number of LSPs towards the egress • Bandwidth has to be increased on downstream legs 69th IETF Chicago July 2007

  11. Savings and Issues with MP2P • MP2P LSPs give: • Good scaling of LSP numbers near egress • No benefit near ingress • Particularly good on ladder topologies • LSP numbers is not everything! • LSP state scales slightly less well • Traffic disambiguation may be needed • Same issue as LDP – what is the source? • New functional controls needed • Control of merging lies with the ingress or the egress? • Management of explicit routes • Resource sharing or resource increments? • New protocol extensions needed • To control the function above • For OAM 69th IETF Chicago July 2007

  12. Next Steps • Close off this I-D with a little more polish • Progress to RFC as individual submission • Will (presumably) attract MPLS WG review in last call • Persuade community that the problem is real • Encourage implementers to develop solutions • MP2P first proposal in draft-yasukawa-mpls-mp2p-rsvpte-02.txt • Happy to see any solution 69th IETF Chicago July 2007

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