IP packet Format

The service provided by the network layer is the forwarding of packets between different network segments.

IP packet Structure

1, Format (4byte*5 per line)

2, Version V4 V6

3, Header length 20 (fixed) + variable length

? , Differentiated Services

Win2008 start: Gpedit.msc set DSCP value

5, total length

Set the meaning of the head length: Because the IP header has a mutable part. Head length measurement head length, total length-head length = data length .

6, packet fragmentation

Why Shard?

Maximum allowable 1500byte for the data link layer.

The IP layer allows a maximum of 2 12 (total length 2byte) of 65535 bytes.

Id

Packet size:

Data Link layer data: 1500byte MTU min 64byte----1500byte mac Layer (14+4=18byte)

Packet: If not fragmented, the maximum is 1480 bytes. 46byte-----1500byte.

7,ttl

7.1,win7 Ping Ciscoiso

7.2,win server TTL 128

8. Agreement Number

ICMP 1 IGMP2 tcp:6 udp:17. Who should be given the data to deal with.

9, Header Checksum

The CRC is not used because the TTL changes every time.

10: Options available

Meaning: In order to increase the function of the IP header. (Increases the overhead of the router)

IP packet Format