Cisco Nexus 7000 Series - Ipv4 Packet Header; Simplified Ipv6 Packet Header

Send document comments to nexus7k-docfeedback@cisco.com.
3-9
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 3 Configuring IPv6
Information About IPv6
IPv4 Packet Header
The basic IPv4 packet header has 12 fields with a total size of 20 octets (160 bits) (see Figure 3-8). The
12 fields may be followed by an Options field, which is followed by a data portion that is usually the
transport-layer packet. The variable length of the Options field adds to the total size of the IPv4 packet
header. The shaded fields of the IPv4 packet header are not included in the IPv6 packet header.
Figure 3-8 IPv4 Packet Header Format
Simplified IPv6 Packet Header
The basic IPv6 packet header has 8 fields with a total size of 40 octets (320 bits) (see Figure 3-9).
Fragmentation is handled by the source of a packet and checksums at the data link layer and transport
layer are used. The User Datagram Protocol (UDP) checksum checks the integrity of the inner packet
and the basic IPv6 packet header and Options field are aligned to 64 bits, which can facilitate the
processing of IPv6 packets.
Table 3-2 lists the fields in the basic IPv6 packet header.
Version Hd Len Type of Service Total Length
20
octets
Identification Flags Fragment Offset
Time to Live Protocol Header Checksum
Source Address
Destination Address
Data Portion
32 bits
Options Padding
Variable
length
51457
Table 3-2 Basic IPv6 Packet Header Fields
Field Description
Version Similar to the Version field in the IPv4 packet header, except that the
field lists number 6 for IPv6 instead of number 4 for IPv4.
Traffic Class Similar to the Type of Service field in the IPv4 packet header. The
Traffic Class field tags packets with a traffic class that is used in
differentiated services.
Flow Label New field in the IPv6 packet header. The Flow Label field tags
packets with a specific flow that differentiates the packets at the
network layer.
Payload Length Similar to the Total Length field in the IPv4 packet header. The
Payload Length field indicates the total length of the data portion of
the packet.