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CRIO: Scaling IP Routing with the Core Router-Integrated Overlay. Xinyang (Joy) Zhang Paul Francis Jia Wang Kaoru Yoshida. Internet Architecture Board Routing Workshop (Oct 2006).

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Crio scaling ip routing with the core router integrated overlay

CRIO:Scaling IP Routing with the Core Router-Integrated Overlay

Xinyang (Joy) Zhang Paul Francis Jia Wang Kaoru Yoshida

Internet architecture board routing workshop oct 2006
Internet Architecture BoardRouting Workshop (Oct 2006)

  • It was clear at the workshop, and probably clearly evident elsewhere, that if there is a highest ranked “problem” in the routing space then it would be that of scaling the routing system

  • It appears that unbounded continued growth of the routing and forwarding system in the Internet appears to trigger off some real limitations relating to hardware design and switching centre infrastructure

---- Geoff Huston

Why is scaling a problem


Active BGP entries (FIB)





Why is Scaling a Problem?

  • A glimpse of current routing system:

    • Static table size

      • Global IPv4 : ~ 200K entries

      • VPN: ~800K entries

      • And more routes are coming: IPV6, traffic-engineered, etc.

    • Routing Dynamics

      • BGP update churns

      • Persistent instabilities

      • Long convergence time (due to damping and MRAI timer)

  • Looking into the future:

    • Can we support a routing table twice (or 10 times) the size of today?

    • Can we rely on the hardware advances to alleviate the scaling pressure?

  • This talk is about the static

  • characteristics of the scaling

  • Validity of CRIO approach

Crio s approach to scaling
CRIO’s Approach to Scaling

  • Tunneling

    • Revisit old idea (by Deering)

    • Decouples addressing from topology

  • Virtual Prefix

    • Novel approach

    • Greatly shrink forwarding table

Crio tunneling an illustration
CRIO Tunneling: an Illustration

Prefix TE Source

Mapping Adv.


PE2 ---- BGP

Prefix TE Source PE2 Mapping ---- BGP/OSPF PE3 Mapping

Provider Networks





Routing Adv.




Customer Site C2

Customer Site C1

Crio tunneling benefits
CRIO Tunneling: Benefits

  • Separate Mapping from Routing

    • BGP only computes routes to TE prefixes

      • On the order of one thousand entries

      • Stable ISP provisioned prefixes

    • Mappings are easy to distribute

      • A mapping entry is the same no matter where it appears

    • Support multi-homing without burdening the routing system

What about router s forwarding table
What about router’s forwarding table?

  • CRIO tunneling can not shrink forwarding information

  • Forwarding table is expected to get larger

    • Since CRIO supports for fine-grained multi-homing

  • Benefits for having small forwarding tables

    • Smaller memory requirement on routers’ line cards

    • Faster transfer for forwarding table updates

Crio virtual prefix an illustration
CRIO Virtual Prefix: an Illustration

  • A virtual prefix is a super-prefix that spans a large portion of the address space

  • Routers that advertise a given virtual prefix must hold the mappings for every prefix within the virtual prefix

Prefix TE Source

Routing Adv.

PE2 ---- BGP PE2 Mapping PE4 Mapping








Prefix TE Source

PE2 ---- BGP

PE3 ---- BGP ---- BGP PE2 Mapping PE4 Mapping

Crio virtual prefix trade off
CRIO Virtual Prefix: Trade-off

  • Virtual prefixes provide a tuning knob for the router

    • trade-off forwarding table size for path length

    • Per-prefix basis

  • It’s a good trade-off to make

    • Few prefixes handle most traffic (power law)

    • Routers could shed most of their prefixes with very little overall increase in traffic volume

    • Save routers from handling large amount of mapping updates

  • Virtual Prefix is particularly suitable for VPNs

Crio evaluation static analysis
CRIO Evaluation: Static Analysis

  • Evaluate the static performance of CRIO by simulation

    • Quantify table size vs. path length tradeoff

    • Simulated both Global Internet and VPN

      • Based on actual Internet topology & ISP traffic matrices

    • Simulation tool: C-BGP

Crio evaluation data collection
CRIO Evaluation: Data Collection

  • Global Internet

    • Topology:

      • POP-level from RocketFuel

      • 23 Tier-1 ISP, 1219 POPs, 4159 inter-POP links

    • Mappings:

      • Derived <prefix, TE> mappings from RocketFuel raw traces

    • Internet Traffic Matrices:

      • Prefix-level, across all POP in our topology

      • Use Netflow records from Tier-1 ISP backbone

  • VPN

    • Same data is collected for VPN from a large VPN provider and one of its national-sized customers

Crio evaluation forwarding table content


CRIO Evaluation: Forwarding Table Content

  • Direct Entries

  • Virtual Prefix Entries

  • “Extra” Path-Shrinking Entries

Routing Adv.

Prefix TE Source

PE2 ---- BGP

PE3 PE2 Mapping





Prefix TE Source

Prefix TE Source

PE2 ---- BGP ---- BGP

PE3 ---- BGP ---- BGP PE2 Mapping

Crio evaluation virtual prefix placement policy

Prefix TE Source

Prefix TE Source

PE2 ---- BGP

PE2 ---- BGP PE2 Mapping PE2 Mapping




Prefix TE Source

Prefix TE Source

Prefix TE Source ---- BGP

PE3 ---- BGP

PE4 ---- BGP ---- BGP ---- BGP

CRIO Evaluation: Virtual Prefix Placement Policy

  • Inter-ISP (Random)

  • Intra-ISP

  • Intra-ISP shortest customer path

Routing Adv.

Routing Adv.

Provider 2

Provider 1





Crio global internet simulation results

Path-length vs. Table-size Trade-off

Virtual Prefix does increase the path length

Average path length converges quickly as the # path-shrinking entries increases

Reduce FIB size by 3-5 times with very little path length penalty

CRIO Global Internet Simulation Results

Increase the percentage of shortest path traffic

by increasing # of Path-Shrinking Entries

99% Traffic uses shortest path

Crio vpn simulation results one customer
CRIO VPN Simulation Results (One Customer)

  • Hub-Spoke nature of VPN traffic exploits the tradeoff better

  • Reduce table size by 10-20 times with very little path length penalty

Cumulative Distribution of PE Routers

PE Routers

In Hub Sites


  • CRIO is a new routing architecture, aimed to provide

    • Scalable and stable core routing

      • Reduce BGP RIB by two order of magnitude

    • FIB size reduction

      • Reduce FIB by one order of magnitude for global Internet, 10-20x for VPN

Future work
Future Work

  • Design and implement the mapping distribution infrastructure

  • Study the dynamics aspect of CRIO

  • Study the security aspect of CRIO

  • Explore the use of CRIO to provide traffic engineering for multi-homed site

  • Address (??) new management challenges