What does the IPv6 next header field mean?

The next header field is an 8-bit value that tells the receiver what protocol follows the IPv6 base header. Common values are 6 for TCP, 17 for UDP, 58 for ICMPv6, and 43 for a routing extension header. The parser shows the numeric value and the matching protocol name when available.

How is IPv6 different from IPv4?

IPv6 uses a fixed 40-byte base header, 128-bit addresses, and a flow label for QoS. IPv4 headers are variable length from 20 to 60 bytes, use 32-bit addresses, and include a header checksum. When you parse an IPv6 packet with ByteLens, the byte grid immediately shows the larger address fields and simpler header layout.

What is the IPv6 flow label used for?

The 20-bit flow label marks a sequence of packets that should receive consistent handling, such as the same path or scheduling treatment. The parser extracts the flow label from the first four bytes of the header and displays it in decimal and hex for quick inspection.

Can this parser decode IPv6 extension headers?

ByteLens IPv6 Parser currently decodes the 40-byte fixed base header and the next header value. It does not recursively decode extension headers or the transport payload, but you can read the remaining bytes as raw hex and paste them into the TCP, UDP, or ICMPv6 parser when the next header points to one of those protocols.

IPv6 Parser - Decode IPv6 Packets Online

Name: IPv6 Protocol Visualizer
Author: ByteLens

IPv6 Packet Parser Online

ByteLens IPv6 Parser turns a raw IPv6 packet hex dump into a clear field breakdown. Paste any complete IPv6 header to see the version, traffic class, flow label, payload length, next header, hop limit, source address, and destination address. The parser validates the hex string, maps each byte to its field, and highlights the corresponding bytes in the grid.

IPv6 Header Format

The IPv6 base header is a fixed 40 bytes. It starts with a 4-bit version field set to 6, followed by an 8-bit traffic class, a 20-bit flow label, a 16-bit payload length, an 8-bit next header field, and an 8-bit hop limit. The header ends with a 128-bit source address and a 128-bit destination address.

Version (4 bits): always 6 for IPv6 packets.
Traffic Class (8 bits): carries DSCP and ECN values for quality of service.
Flow Label (20 bits): marks a packet sequence that should receive consistent handling.
Payload Length (16 bits): the number of bytes after the fixed header.
Next Header (8 bits): identifies the protocol that follows, such as TCP, UDP, or an extension header.
Hop Limit (8 bits): decremented by each router; the packet is dropped when it reaches zero.
Source Address (128 bits): the origin IPv6 address.
Destination Address (128 bits): the target IPv6 address.

IPv6 Packet Example

Explore real IPv6 samples to see how each field behaves:

Next Header Field Explained

The next header field replaces the IPv4 protocol field and tells the receiver how to interpret what follows the fixed header. Common values include 6 for TCP, 17 for UDP, 58 for ICMPv6, and 43 for routing extension headers. Learn more in the IPv6 header guide.

IPv6 vs IPv4 Header Differences

IPv6 simplifies the IP header compared with IPv4. The IPv6 base header is always 40 bytes, while IPv4 headers vary from 20 to 60 bytes because of options. IPv6 removes the header checksum, so upper-layer protocols handle error detection. Address size grows from 32 bits to 128 bits, and the IPv4 TTL field becomes the IPv6 hop limit. Compare both headers side by side on the IPv4 vs IPv6 comparison page, or open the IPv4 parser to see the older format.

Parse IPv6 UDP/TCP Packets

IPv6 does not change UDP or TCP semantics, only the encapsulation. When the next header value is 17, the payload begins with a UDP header. When it is 6, the payload begins with a TCP header. Paste a combined hex dump into the parser above to inspect the IPv6 base fields first, then continue reading the transport header bytes.

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