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IP Address Lookup

IP Address Lookup. Masoud Sabaei Assistant professor Computer Engineering and Information Technology Department, Amirkabir University of Technology. Outlines. Overview, Trie-based Algorithms, Hardware-based Schemes, IPV6 Lookup. IP Routing. Packet forwarding tasks

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IP Address Lookup

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  1. IP Address Lookup Masoud Sabaei Assistant professor Computer Engineering and Information Technology Department, Amirkabir University of Technology

  2. Outlines • Overview, • Trie-based Algorithms, • Hardware-based Schemes, • IPV6 Lookup

  3. IP Routing • Packet forwarding tasks • Packet header encapsulation and decapsulation • Updating TTL field • Checking for errors • … • IP route lookup -> Dominates the processing time

  4. IP Address Bit Position

  5. IP Address Lookup

  6. Routing Table at Each Node

  7. Hierarchical Routing

  8. Net ID Host ID Hierarchical Routing

  9. Router’s Forwarding Table Structure

  10. IP Routing – Classful and Classless

  11. Prefix Aggregation

  12. Prefix Ranges

  13. Exception Prefix

  14. IP Routing – Classless • Classless Interdomain Routing (CIDR) • Arbitrary aggregation • Arbitrary length for host and network fields • Routing entry: <prefix/length> pair • <12.0.54.8/32> • <12.0.54.0/24> • <12.0.0.0/16> • Efficient routing table size • Needs to find the longest match • Packet destination: 12.0.54.2 • Matches: <12.0.54.0/24>, <12.0.0.0/16> • <12.0.54.0/24> is used • Makes IP route lookup a bottleneck

  15. Table Growth of a Typical Backbone Router

  16. Prefix Length Distribution of a Typical Backbone Router

  17. IP Address lookup design • Goals • Minimize time (primary goal) • Minimize the number of memory accesses • Minimize the size of the data structure • Minimize instructions needed • Aligned data structures

  18. Address Lookup Structure • IP address space • A binary tree with depth 32 • 232 leaves • <prefix/length> pair • Prefix defines a path in the tree • Length says how deep the path goes in the tree • All IP addresses in the subtree are routed according that entry • Longest matching concept • Subtrees of entries e1 and e2 overlap • e1 is hidden by e2 for addresses in the range r

  19. IP Address Lookup and Caching • Using caching techniques for IP address lookup • Relies on locality of destination address stream • There is not enough locality for backbone routers • Not a good solution for current backbone routers

  20. Performance Metrics for Comparison IP Address Lookup Algorithms • Lookup Speed, • Storage Requirement, • Update Time, • Scalability, • Flexibility in Implementation.

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