The IPv6 source address field is a 128-bit header field containing the IPv6 address of the host that sent the packet. It identifies the packet’s origin at Layer 3. section 20.3.1 section 7.4
Keep these practical points in mind:
- Find the field in the fixed 40-byte IPv6 header, alongside the destination address field. section 20.3.1
- Distinguish the source address from the destination address: one identifies the sender, while the other identifies the intended recipient. section 7.1.9 section 20.3.1
- Treat detailed field positions as context rather than a memorization target for the CCNA exam. section 20.3.1 section 7.1
Reading an IPv6 header diagram
In the IPv6 header layout, locate Source Address after Hop Limit and before Destination Address; the diagram shows both as address fields within the 40-byte header. section 20.3.1
Figure 20.2 The format of the IPv6 header. The fields are Version, Traffic Class, Flow Label, Payload Length, Next Header, Hop Limit, Source Address, and Destination Address. The header is 40 bytes in size.
Use the IPv6 header diagram to see the source address field’s position, neighboring fields, and relationship to the destination address. section 20.3.1
