IP Packet

April 20, 2023 IP Packet 2

Packet Format

Version HLen TOS Length

Ident Flags Offset

TTL Protocol Checksum

SourceAddr

DestinationAddr

Options (variable) Pad(variable)

0 4 8 16 19 31

Data

April 20, 2023 IP Packet 3

Packet Format

• Version—Versi IP yang digunakan (0100=4) • IP Header Length (IHL)—Datagram header length dalam

32-bit words. • Type-of-Service—Specifies how an upper-layer protocol

would like a current datagram to be handled, and assigns datagrams various levels of importance.

• Total Length—Panjang paket dalam bytes, termasuk data dan header.

• Identification—Nilai integer ebagai identifikasi paket saat ini. Item ini berguna pada fragmentation jika paket terdiri atas potongan-potongan paket besar

April 20, 2023 IP Packet 4

Packet Format

• Flags—Consists of a 3-bit field of which the two low-order (least-significant) bits control fragmentation. – The low-order bit specifies whether the packet can be fragmented.

– The middle bit specifies whether the packet is the last fragment in a series of fragmented packets.

– The third or high-order bit is not used.

• Fragment Offset—Indicates the position of the fragment's data relative to the beginning of the data in the original datagram, which allows the destination IP process to properly reconstruct the original datagram.

April 20, 2023 IP Packet 5

Packet Format

• Time-to-Live—Maintains a counter that gradually decrements down to zero, at which point the datagram is discarded. This keeps packets from looping endlessly.

• Protocol—Indicates which upper-layer protocol receives incoming packets after IP processing is complete.

• Header Checksum—Helps ensure IP header integrity. • Source Address—Specifies the sending node. • Destination Address—Specifies the receiving node. • Options—Allows IP to support various options, such as

security. • Data—Contains upper-layer information.

April 20, 2023 IP Packet 6

Fragmentation and Reassembly

R2

R1

H4

H5

H3H2H1

Network 2 (Ethernet)

H6

Network 3 (FDDI)

Network 4(point-to-point)

Network 1 (Ethernet)

R3 H7 H8

R1R2

R3

April 20, 2023 IP Packet 7

Fragmentation and Reassembly

R1

ETH FDDI

IPIP

ETH

TCP R2

FDDI PPP

IP

R3

PPP ETH

IP

H1

IP

ETH

TCP

H8

H1 R1 R2 R3 H8

ETHIP (1400) FDDIIP (1400) PPPIP(512)

PPPIP(376)

PPPIP(512)

ETHIP(512)

ETHIP(376)

ETHIP(512)

April 20, 2023 IP Packet 8

Ident = x Offset = 0

Start of header

0

Rest of header

1400 data bytes

H1 R1 R2 R3 H8

ETHIP (1400) FDDIIP (1400) PPPIP(512)

PPPIP(376)

PPPIP(512)

ETHIP(512)

ETHIP(376)

ETHIP(512)

Ident = x Offset = 0

Start of header

1

Rest of header

512 data bytes

Ident = x Offset = 512

Start of header

1

Rest of header

512 data bytes

Ident = x Offset = 1024

Start of header

0

Rest of header

376 data bytes

IP Header = 4x5 = 20 bytes