1 / 18

CSCE 515 : Computer Network Programming

CSCE 515 : Computer Network Programming. Chin-Tser Huang huangct@cse.sc.edu University of South Carolina. Open Shortest Path First (OSPF). A link-state routing protocol Each router tests status of all its links and broadcasts its link status to all routers on network

julianne-morin
Download Presentation

CSCE 515 : Computer Network Programming

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CSCE 515:Computer Network Programming Chin-Tser Huang huangct@cse.sc.edu University of South Carolina

  2. Open Shortest Path First (OSPF) • A link-state routing protocol • Each router tests status of all its links and broadcasts its link status to all routers on network • Use IP to carry its message • Provide features superior to RIP

  3. OSPF Message Format 1 1 2 4 4 2 2 8 ver- sion type packet length router ID area ID checksum auth type authentication data

  4. Autonomous Systems • A collection of networks administered by single entity, e.g. a corporation or a campus • Three categories of AS • Stub AS • Multihomed AS • Transit AS

  5. Example of Autonomous System Source: Internetworking Technologies Handbook by Cisco Press

  6. IGP and EGP • Each AS selects its interior gateway protocol (IGP) for communications between routers in this AS • E.g. RIP, OSPF • Multiple AS’s use exterior gateway protocol (EGP) for communications between routers in different AS’s • E.g. EGP, BGP

  7. Border Gateway Protocol (BGP) • An exterior gateway protocol • Distance-vector protocol but enumerates route to each destination • Allow policy-based routing • Use TCP to transport its messages

  8. Classless Interdomain Routing (CIDR) • Solve two problems • Shortage of class B network IDs • Explosion in routing table size due to allocation of multiple class C network IDs • Summarize multiple IP addresses into a smaller number of routing table entries

  9. Requirements of CIDR • Multiple IP addresses to be summarized need to share same high-order bits • Routing decisions need to be based on 32-bit IP address and 32-bit mask • Routing protocols need to carry 32-bit mask in addition to 32-bit address

  10. Example of CIDR CIDR Block Prefix # Equivalent Class C # of Host Addresses /27 1/8th of a Class C 32 hosts /26 1/4th of a Class C 64 hosts /25 1/2 of a Class C 128 hosts /24 1 Class C 256 hosts /23 2 Class C 512 hosts … /15 512 Class C 131,072 hosts /14 1,024 Class C 262,144 hosts /13 2,048 Class C 524,288 hosts

  11. User Datagram Protocol (UDP) • A datagram-oriented transport layer protocol • Each output operation by a process produces exactly one UDP datagram • Provide no reliability

  12. source port number destination port number UDP length UDP checksum data (if any) UDP Header 0 15 16 31 8 bytes

  13. UDP Checksum • Cover UDP header and UDP data • End-to-end checksum calculated by sender and verified by receiver • Should always be enabled • 16-bit one’s complement sum of header (including a pseudo header) and data is calculated

  14. Computation of UDP Checksum 0 15 16 31 source IP address destination IP address UDP pseudo header zero protocol(17) UDP length source port number destination port number UDP header UDP length UDP checksum data (if any) pad byte(0)

  15. Fragmentation • Need to fragment if size of resulting IP datagram exceeds MTU • Can take place at source or at an intermediate router • Fragments are reassembled at destination

  16. Example of UDP Fragmentation IP header UDP header UDP data 20 8 1473 IP header UDP header IP header 20 8 1472 20 1

  17. ICMP Unreachable Error (Fragmentation Required) 0 7 8 15 16 31 type(3) code(0-15) checksum unused (must be 0) MTU of next-hop network IP header + first 8 bytes of original datagram data

  18. Next Class • UDP • Broadcasting and multicasting • Class MulticastSocket • Read TI Ch. 11, 12, JNP Ch. 22

More Related