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Configuration Guide - IP Service

CloudEngine 12800 and 12800E V200R005C00

This document describes the configurations of IP Service, including IP address, ARP, DHCP, DNS, IP performance optimization, IPv6, DHCPv6, and IPv6 DNS.
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DHCPv6 Packets

DHCPv6 Packets

Similar to DHCP for IPv4, DHCPv6 clients and DHCPv6 servers exchange DHCPv6 messages using the User Datagram Protocol (UDP). DHCPv6 clients only process DHCPv6 messages with UDP port number 546. DHCPv6 servers and relay agents only process DHCPv6 messages with UDP port number 547.

DHCPv6 Packet Format

  • Format of messages exchanged between DHCPv6 clients and DHCPv6 servers

    Figure 8-2 shows the format of messages exchanged between DHCPv6 clients and DHCPv6 servers.

    Figure 8-2 Format of messages exchanged between DHCPv6 clients and DHCPv6 servers

    Table 8-1 Fields of messages exchanged between DHCPv6 clients and DHCPv6 servers

    Field

    Length

    Description

    msg-type

    1 byte

    Indicates the packet type. The value ranges from 1 to 11. For details, see the DHCPv6 Packet Type.

    transaction-ID

    3 bytes

    Identifies packet transaction between DHCPv6 clients and servers. For example, a DHCPv6 client initiates a Solicit/Advertise transaction or a Request/Reply transaction. Their transaction IDs are different. Transaction IDs have the following characteristics:
    • The transaction ID is randomly generated by a DHCPv6 client.
    • Transaction IDs of request and reply packets must be the same.
    • The transaction ID of a packet initiated by a DHCPv6 server is 0.

    Options

    Variable

    Indicates the option field in a DHCPv6 packet. The option field contains configurations that the DHCPv6 server assigns to IPv6 hosts, such as the IPv6 address of the DNS server.

    For details, see Options Field in a DHCPv6 Message.

  • Format of messages exchanged between DHCPv6 relay agents and DHCPv6 servers

    Figure 8-3 shows format of messages exchanged between DHCPv6 relay agents and DHCPv6 servers.

    Figure 8-3 Format of messages exchanged between DHCPv6 relay agents and DHCPv6 servers

    Table 8-2 Fields of messages exchanged between DHCPv6 relay agents and DHCPv6 servers

    Field

    Length

    Description

    msg-type

    1 byte

    Indicates the message type. The value ranges from 12 (RELAY-FORW) to 13 (RELAY-REPL). For details, see DHCPv6 Message Type.

    hop-count

    1 byte

    Indicates the number of DHCPv6 relay agents that a DHCPv6 message has passed through.

    link-address

    16 bytes

    Indicates an IPv6 global unicast or link-local address that will be used by a server to identify the link to which a client is connected.

    peer-address

    16 bytes

    Indicates the IPv6 address of a client or relay agent from which the message to be relayed was received.

    options

    Variable

    Indicates the Options field in a DHCPv6 message. The Relay Message option must be included.

    For details, see Options Field in a DHCPv6 Message.

DHCPv6 Packet Type

DHCPv6 defines 13 types of packets. A DHCPv6 server and a DHCPv6 client communicate by exchanging these types of packets. Table 8-3 lists DHCPv6 packets and their corresponding DHCPv4 packets and describes the DHCPv6 packets.

Table 8-3 Comparisons between DHCPv6 packets and DHCPv4 packets
DHCP Packet Type DHCPv6 Packet DHCPv4 Message Description
1 SOLICIT DHCP DISCOVER A DHCPv6 client sends a Solicit packet to locate DHCPv6 servers.
2 ADVERTISE DHCP OFFER A DHCPv6 server sends an Advertise packet in response to a Solicit packet to declare that it can provide DHCPv6 services.
3 REQUEST DHCP REQUEST A DHCPv6 client sends a Request packet to request IPv6 addresses and other configuration parameters from a DHCPv6 server.
4 CONFIRM - A DHCPv6 client sends a Confirm packet to any available DHCPv6 server to check whether the obtained IPv6 address applies to the link that the DHCPv6 client is connected to.
5 RENEW DHCP REQUEST A DHCPv6 client sends a Renew packet to the DHCPv6 server that provides the IPv6 addresses and other configuration parameters to extend the lifetime of the addresses and to update configuration parameters.
6 REBIND DHCP REQUEST A DHCPv6 client sends a Rebind packet to any available DHCPv6 server to extend the lifetime of the assigned IPv6 address and to update configuration parameters when the client does not receive a response to its Renew packet.
7 REPLY DHCP ACK/NAK

A DHCPv6 server sends a Reply packet in the following situations:

  1. A DHCPv6 server sends a Reply packet containing IPv6 addresses and configuration parameters in response to a Solicit, Request, Renew or Rebind packet received from a DHCPv6 client.
  2. A DHCPv6 server sends a Reply packet containing configuration parameters in response to an Information-Request packet.
  3. A DHCPv6 server sends a Reply packet in response to a Confirm, Release, or Decline packet received from a DHCPv6 client.
8 RELEASE DHCP RELEASE A DHCPv6 client sends a Release packet to the DHCPv6 server that assigns IPv6 addresses to the DHCPv6 client, indicating that the DHCPv6 client will no longer use the obtained addresses.
9 DECLINE DHCP DECLINE A DHCPv6 client sends a Decline packet to a DHCPv6 server, indicating that the IPv6 addresses assigned by the DHCPv6 server are already in use on the link to which the DHCPv6 client is connected.
10 RECONFIGURE - A DHCPv6 server sends a Reconfigure packet to a DHCPv6 client, informing the DHCPv6 client that the DHCPv6 server has new addresses or updated configuration parameters.
11 INFORMATION-REQUEST DHCP INFORM A DHCPv6 client sends an Information-Request packet to a DHCPv6 server to request configuration parameters except for IPv6 addresses.
12 RELAY-FORW - A DHCPv6 relay agent sends a Relay-Forward packet to relay Request packets to DHCPv6 servers.
13 RELAY-REPLY - A DHCPv6 server sends a Relay-Reply packet to a DHCPv6 relay agent. The Relay-Reply packet carries a packet that the DHCPv6 relay agent needs to deliver to a DHCPv6 client.
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Updated: 2019-04-18

Document ID: EDOC1100039535

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