DOC PREVIEW
WMU CS 5550 - IP Overview

This preview shows page 1-2-3-4-5 out of 15 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 15 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 15 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 15 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 15 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 15 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 15 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

IP Header&IP FragmentationBased on the slides of Dr. Jorg Liebeherr, University of Virginia 20 bytes ≤ Header Size <24x 4 bytes = 60 bytes 20 bytes ≤ Total Length <216 bytes = 65536 bytesIP Datagram FormatECNversionheaderlengthDS total length (in bytes)Identification Fragment offsetsource IP addressdestination IP addressoptions (0 to 40 bytes)payload4 bytestime-to-live (TTL) protocol header checksumbit # 0 15 23 248317160MFDFIP Datagram Format Question: In which order are the bytes of an IP datagram transmitted? Answer: Transmission is row by row For each row:1. First transmit bits 0-72. Then transmit bits 8-153. Then transmit bits 16-234. Then transmit bits 24-31 This is called network byte order or big endian byte ordering.  Note: Many computers (incl. Intel processors) store 32-bit words in little endian format. Others (incl. Motorola processors) use big endian.Big endian vs. small endianLittle Endian Stores the low-order byte at the lowest address and the highest order byte in the highest address. Base Address+0 Byte0 Base Address+1 Byte1 Base Address+2 Byte2 Base Address+3 Byte3  Intel processors use this orderBig Endian Stores the high-order byte at the lowest address, and the low-order byte at the highest address. Base Address+0 Byte3 Base Address+1 Byte2 Base Address+2 Byte1 Base Address+3 Byte0Motorola processors use big endian.• Conventions to store a multibyte work• Example: a 4 byte Long Integer Byte3 Byte2 Byte1 Byte0Fields of the IP Header Version (4 bits): current version is 4, next version will be 6. Header length (4 bits): length of IP header, in multiples of 4 bytes DS/ECN field (1 byte) This field was previously called as Type-of-Service (TOS) field. The role of this field has been re-defined, but is “backwards compatible” to TOS interpretation Differentiated Service (DS) (6 bits): Used to specify service level (currently not supported in the Internet) Explicit Congestion Notification (ECN) (2 bits): New feedback mechanism used by TCPFields of the IP Header Identification (16 bits): Unique identification of a datagram from a host. Incremented whenever a datagram is transmitted Flags (3 bits):  First bit always set to 0 DF bit (Do not fragment) MF bit (More fragments) Will be explained laterÆ FragmentationFields of the IP Header Time To Live (TTL) (1 byte): Specifies longest paths before datagram is dropped Role of TTL field: Ensure that packet is eventually dropped when a routing loop occursUsed as follows: Sender sets the value (e.g., 64) Each router decrements the value by 1 When the value reaches 0, the datagram is droppedFields of the IP Header Protocol (1 byte): Specifies the higher-layer protocol. Used for demultiplexing to higher layers.Header checksum (2 bytes): A simple 16-bit long checksum which is computed for the header of the datagram.Fields of the IP Header Options: Security restrictions Record Route: each router that processes the packet adds its IP address to the header. Timestamp: each router that processes the packet adds its IP address and time to the header. (loose) Source Routing: specifies a list of routers that must be traversed. (strict) Source Routing: specifies a list of the only routers that can be traversed. Padding: Padding bytes are added to ensure that header ends on a 4-byte boundaryMaximum Transmission Unit Maximum size of IP datagram is 65535, but the data link layer protocol generally imposes a limit that is much smaller Example:  Ethernet frames have a maximum payload of 1500 bytesÆ IP datagrams encapsulated in Ethernet frame cannot be longer than 1500 bytes The limit on the maximum IP datagram size, imposed by the data link protocol is called maximum transmission unit (MTU) MTUs for various data link protocols:Ethernet: 1500 FDDI: 4352802.3: 1492 ATM AAL5: 9180802.5: 4464 PPP: negotiatedIP FragmentationFDDIRingRouterHost AHost BEthernetMTUs: FDDI: 4352 Ethernet: 1500• Fragmentation: • IP router splits the datagram into several datagram• Fragments are reassembled at receiver What if the size of an IP datagram exceeds the MTU?IP datagram is fragmented into smaller units. What if the route contains networks with different MTUs?Where is Fragmentation done? Fragmentation can be done at the sender or at intermediate routers The same datagram can be fragmented several times. Reassembly of original datagram is only done at destination hosts !!RouterIP datagram H Fragment 1 H1Fragment 2 H2What’s involved in Fragmentation? The following fields in the IP header are involved:Identification When a datagram is fragmented, the identification is the same in all fragmentsFlagsDF bit is set: Datagram cannot be fragmented and must be discarded if MTU is too smallMF bit set: This datagram is part of a fragment and an additional fragment follows this oneWhat’s involved in Fragmentation? The following fields in the IP header are involved:Fragment offset Offset of the payload of the current fragment in the original datagramTotal length Total length of the current fragmentExample of Fragmentation A datagram with size 2400 bytes must be fragmented according to an MTU limit of 1000 bytesDetermining the length of fragments To determine the size of the fragments we recall that, since there are only 13 bits available for the fragment offset, the offset is given as a multiple of eight bytes. As a result, the first and second fragment have a size of 996 bytes (and not 1000 bytes). This number is chosen since 976 is the largest number smaller than 1000–20= 980 that is divisible by eight. The payload for the first and second fragments is 976 bytes long, with bytes 0 through 975 of the original IP payload in the first fragment, and bytes 976 through 1951 in the second fragment. The payload of the third fragment has the remaining 428 bytes, from byte 1952 through 2379. With these considerations, we can determine the values of the fragment offset, which are 0, 976 / 8 = 122, and 1952 / 8 = 244, respectively, for the first, second and third fragment.Internet Control Message Protocol (ICMP)Based on the slides of Dr. Jorg Liebeherr, University of Virginia The IP (Internet Protocol) relies on several other protocols to perform necessary control and routing functions: Control functions (ICMP) Multicast signaling (IGMP) Setting up routing tables


View Full Document

WMU CS 5550 - IP Overview

Download IP Overview
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view IP Overview and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view IP Overview 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?