1. ECE 526 – Network Processing Systems Design Packet Processing II: algorithms and data structures Chapter 5: D. E. Comer

2. Ning WengECE 5262 Goal and Outline Goal: ─ Understand basic network processing operations ─ Learn how to perform operations – data structures & algorithms Outline: ─ IP fragmentation and reassembly ─ IP forwarding and routing ─ TCP connection recognition and splicing ─ Summary ─ For next class

3. Ning WengECE 5263 IP Fragmentation Needed when datagram larger than network MTU ─ Ethernet 1500 Byte FLAGs bits in datagram header

4. Ning WengECE 5264 Fragmentation Example How to identify a fragment ─ Flags ─ Offset: multiple of 64 bit ─ Ident: unique to send machine

5. Ning WengECE 5265 IP Fragmentation Algorithm

6. Ning WengECE 5266 IP Reassembly Process to join fragments and produce original datagram Only ultimate destination perform IP reassembly (NAT: exception) Four factors influencing reassembly ─ Out of order delivery ─ Duplication ─ Loss ─ Concurrent reception Key fields help reassembly ─ Source IP address ─ ID field ─ Flags and Offset

7. Ning WengECE 5267 Reassembly Algorithm

8. Ning WengECE 5268 Reassembly Data Structure Two parts ─ Buffer larger enough to hold original datagram ─ Linked list of pieces that have arrived

9. Ning WengECE 5269 IP Datagram Forwarding Conceptual mapping ─ (next hop, interface)  f(datagram, routing table) Routing table ─ one entry per destination ─ entry contents: IP address, address mask, next-hop address and N-bit interface number Example IP routing table

10. Ning WengECE 52610 IP Forwarding Algorithm Assuming: routing table sorted from most specific to less specific Can I use hashing?

11. Ning WengECE 52611 High-Speed Forwarding Example routing tree

12. Ning WengECE 52612 Routing Exercises Draw tire of the following prefixes: ─ A: 0010* ─ B: 010* ─ C: 0101* ─ D: 0* ─ E: 10* ─ F: 1011* ─ G: 100* Which prefixes match the following lookups? ─ 01 ─ 101 ─ 0001 ─ 1

13. Ning WengECE 52613 TCP Connection Recognition Key function of traffic monitors, firewalls and NAT State of TCP connection ─ Being established ─ Completely established ─ Being terminated ─ Completely terminated (remove from record) Code bits in TCP header: ─ Reset: error occurred when one end has no record connection regarded as a completely terminated here ─ Syn: to start new connection completely established need “see” syn from both sides ─ Fin: to terminate connection completely terminated need “see” fin from both sides

14. Ning WengECE 52614 TCP Connection Recognition Algorithm

15. Ning WengECE 52615 TCP Splicing Join two TCP connections ─ Allow data to pass between them ─ To avoid termination overhead ─ By translating segment header fields Acknowledgment number; sequence number

16. Ning WengECE 52616 TCP Splicing Algorithm

17. Ning WengECE 52617 Summary Packet processing operations and algorithms ─ Ethernet bridging (layer 2) ─ IP fragmentation, reassembly and forwarding (layer 3) ─ TCP splicing, connection recognition (layer 4) ─ Flow classification (mixed layer) Important data structure ─ Linked list ─ Hashing table ─ Routing table ─ Tire Table lookup ─ Hashing ─ Full match for layer 2 ─ Longest prefix match (LPM) for layer 3

18. Ning WengECE 52618 For Next Class “Networking Algorithmics” ─ Chapter 17: Network Security (handout)

19. Ning WengECE 52619 Backup