The original design of IPv6 did not include DHCP; all hosts would use SLAAC to calculate their IPv6 address. As noted previously, operators discovered there are still reasons to have a lightweight protocol that supports interface address configuration.
There are some minor differences between DHCP for IPv4 and DHCP for IPv6 (often called DHCPv6):
•Instead of broadcasting responses, the server can send packets to the client’s link local address, thus eliminating all server broadcasts.
•Instead of broadcasting packets intended for the DHCP server, the client sends these packets to a multicast group.
•A server can assign an address to a host based on a DHCP unique identifier (DUID), which is calculated by the client. If the host’s physical address changes, it can keep or recover its previous IPv6 address.
•Many unnecessary and unused options from DHCP for IPv4 have been removed in DHCPv6.
•The discover message in IPv4 DHCP is the solicit message in DHCPv6.
•The offer message in IPv4 DHCP is the advertise message in DHCPv6.
•The acknowledge message in DHCP for IPv4 is the reply message in DHCPv6.
One major difference between DHCP for IPv4 and DHCPv6 is the prefix length and default gateway are not included in the DHCPv6 reply message. Instead, these are carried in a separate IPv6 protocol called Router Advertisements (RAs). Here is the prep course: https://www.acedexam.com/010-151-dctech-supporting-cisco-datacenter-networking-devices/
IPv6-capable routers send RAs to each segment to
•Inform hosts connected to the segment the router can be used as a default gateway.
•Indicate whether hosts connected to this segment should automatically compute their IPv6 addresses via SLAAC or should ask for an address through a DHCPv6 server.
•Inform hosts connected to the segment about the maximum packet size (or maximum transmission unit [MTU]).
Note
The chapters in Part II explore MTU in more detail.
Host-to-Host Communication and Address Resolution on a Single Wire
Once all the hosts connected to a single segment have physical and interface addresses, they can begin to communicate. Figure 3-4 will be used to explain the process.
Figure 3-4 Host-to-Host Communication
In the figure, each host has two addresses: a physical address and an interface address. Host A could send packets destined to host D to the correct interface and broadcast physical addresses. Host D would certainly receive and process the packet in this case, but host B would need to receive the packet, examine it, determine it does not need to accept or process it, and then discard it. If every host on the segment must receive and process every packet—even if the processing is just to discard the packet—this would be a huge waste of resources.
It is much more efficient if host A can send packets to host D’s correct interface and physical addresses. To do this, however, A must know the relationship between these two addresses; it must resolve host D’s interface address to a physical address reachable on this segment.
IPv4 and IPv6 use different address resolution techniques.
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