No relevant resource is found in the selected language.

This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Read our privacy policy>Search

Reminder

To have a better experience, please upgrade your IE browser.

upgrade

NE40E-M2 V800R010C10SPC500 Feature Description - User Access 01

This is NE40E-M2 V800R010C10SPC500 Feature Description - User Access
Rate and give feedback:
Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Principles of DHCPv6 Address Allocation

Principles of DHCPv6 Address Allocation

Principles of the DHCPv6 Server

DHCPv6 servers are responsible for assigning IPv6 addresses/prefixes and other configuration information (such as configuration information about the DNS server) to clients. Clients send Information-Request messages to a specific server to obtain required configuration information. After receiving an Information-Request message, each server replies with a Response message containing the configuration information required by the client according to policies. Both the Request and Response messages are encapsulated in UDP packets.

  • DHCP Unique Identifier (DUID) of a DHCPv6 device

    During the interaction between a DHCPv6 client and a DHCPv6 server, each DHCPv6 client or DHCPv6 server is identified by a unique DUID. On a DHCPv6 server, the client DUID identifies a DHCPv6 client and is used in the local address allocation policy. On a DHCPv6 client, the server DUID is used to identify a DHCPv6 server. DUIDs can be generated in the following modes:

    • DUID Based on Link-layer Address Plus Time (DUID-LLT)

      In DUID-LLT mode, DUIDs are generated for DHCPv6 devices based on link-layer addresses and the time.

    • DUID Assigned by Vendor Based on Enterprise Number (DUID-EN)

      In DUID-EN mode, DUIDs are generated for DHCPv6 devices based on the enterprise numbers registered with the Internet Assigned Numbers Authority (IANA).

    • DUID Based on Link-layer Address (DUID-LL)

      In DUID-LL mode, DUIDs are generated for DHCPv6 devices based on link-layer addresses.

  • DHCPv6 multicast address

    Similar to a DHCPv4 client, a DHCPv6 client does not need to be configured with the IPv6 addresses of DHCPv6 servers. Instead, the DHCPv6 client sends a Solicit message with a multicast destination address to locate DHCPv6 servers. When the DHCPv6 client discovers multiple servers, the client selects a server according to a certain policy (such as the Preference option). In DHCPv6, two multicast addresses are defined:

    • All_DHCP_Relay_Agents_and_Servers (FF02::1:2)

      This multicast address is used by all servers and relay agents in a broadcast domain. When a client initiates DHCPv6 interaction, it interacts with all servers and relay agents through this address.

    • All_DHCP_Servers (FF05::1:3)

      This multicast address is used by all servers in a broadcast domain. When a relay agent needs to forward messages to all servers but it does not know the unicast addresses of the servers, the relay agent can use this multicast address to forward messages.

  • Interaction model between a DHCPv6 client and a DHCPv6 server

    DHCPv6 adopts the client/server model for communications. A client sends an Information-Request message to a specific server for a valid dynamic IPv6 address/prefix or other configuration information. After receiving the Information-Request message, each server replies with a Response message containing the configuration information for the client according to policies. At different stages, DHCPv6 clients and servers exchange different information in different modes:

    • Exchanging configuration information, involving two steps

      • After a client obtains an IPv6 address/prefix in the stateless address configuration manner, it multicasts a DHCPv6 Information-Request message.

      • After a server receives the Information-Request message, it replies with a Response message containing the configuration information for the client.

    • Exchanging IPv6 addresses/prefixes and other configuration information, involving two steps:

      When a client accesses the network for the first time, it can obtain an IPv6 address/prefix and configuration information based on the following steps:

      • When a client accesses the network for the first time, it multicasts a DHCPv6 Solicit message containing the Rapid Commit option.

      • After receiving the DHCPv6 Solicit message from the client, a DHCPv6 server selects an unassigned IPv6 address/prefix from the IPv6 address/prefix pool and assigns it to the client. If the server supports two-step interaction, it sends a DHCPv6 Response message containing the leased IPv6 address/prefix and other configuration information. Otherwise, the server sends a DHCPv6 Advertise message.

      • After receiving the Response message, the client uses the IPv6 address/prefix and other configuration information in the Response message. If the client receives only a DHCPv6 Advertise message within the specified period, the client undergoes four stages to obtain the configuration information according to the configured policy.

      NOTE:

      This situation is applicable to the scenario where only one server exists on the network. Otherwise, IPv6 addresses/prefixes are wasted.

    • Exchanging IPv6 addresses/prefixes and other configuration information, involving four stages:

      When a DHCPv6 client accesses the network for the first time, similar to a DHCPv4 client, the DHCPv6 client undergoes four stages to obtain an IPv6 address/prefix and other configuration information:

      • Discovering stage: indicates the stage at which the DHCPv6 client searches for a DHCPv6 server. The client multicasts a DHCPv6 Solicit message.

      • Offering stage: indicates the stage at which the DHCPv6 server offers an IPv6 address/prefix to the DHCPv6 client. After receiving the DHCPv6 Solicit message from the client, the DHCPv6 server selects an unassigned IPv6 address/prefix from the IPv6 address/prefix pool, and then sends a DHCPv6 Advertise message containing the leased IPv6 address/prefix and other configuration information to the client.

      • Selecting stage: indicates the stage at which the DHCPv6 client selects an IPv6 address/prefix. If multiple DHCPv6 servers send DHCPv6 Advertise messages to the client, the client selects a server according to the configured policy. If the Advertise message contains the Server Unicast option, and the client also supports this option, the client unicasts a DHCPv6 Request message to each DHCPv6 server. Otherwise, the client multicasts a DHCPv6 Request message containing information used to instruct the selected DHCPv6 server to offer an IPv6 address/prefix.

      • Acknowledging stage: indicates the stage at which the DHCPv6 server acknowledges the IPv6 address/prefix to be offered. After receiving the DHCPv6 Request message from the client, the DHCPv6 server sends a DHCPv6 Response message to the client. The DHCPv6 Response message contains the offered IPv6 address/prefix and other configuration information. After receiving the DHCPv6 Response message, the client uses the offered IPv6 address/prefix and other configuration information.

      NOTE:

      Except the address offered by the DHCPv6 server selected by the DHCPv6 client, the unassigned IPv6 addresses/prefixes offered by other DHCPv6 servers are available for other DHCPv6 clients.

    • The DHCPv6 client extends the IPv6 address/prefix lease.

      When a DHCPv6 server assigns an IPv6 address/prefix to a client, the server sends a message containing the preferred lifetime, valid lifetime, lease renew time, and rebind time. The relationship between them is as follows: lease renew time < rebind time < preferred lifetime < valid lifetime.

      The preferred lifetime is used to limit the lease renew time and rebind time. By default, the lease renew time and rebind time account for 50% and 80% respectively of the preferred lifetime.

      The valid lifetime is the lease set for the IPv6 address/prefix assigned to a client. The server retrieves the IPv6 address/prefix after the valid lifetime expires. If the client intends to continue to use this IPv6 address/prefix, it needs to extend the IPv6 address/prefix lease before the valid lifetime ends.

      When the lease of the IPv6 address/prefix expires, the DHCPv6 client automatically sends a DHCPv6 Renew message to the server. If the client and server support unicast, the client unicasts a DHCPv6 Renew message. Otherwise, the client multicasts a DHCPv6 Renew message.

      After the DHCPv6 server receives the DHCPv6 Renew message, if the contained IPv6 address/prefix is valid and the lease can be renewed, the server replies with a DHCPv6 Response message containing the new lease of the IPv6 address/prefix. After receiving the DHCPv6 Response message from the server, the client renews the lease of its IPv6 address/prefix.

      When the rebind time expires, if the DHCPv6 client does not finish renewing the lease of its IPv6 address/prefix, it multicasts a DHCPv6 Rebind message to all available servers.

      After the DHCPv6 server receives the DHCPv6 Rebind message, if the contained IPv6 address/prefix is valid and the lease can be renewed, the server replies with a DHCPv6 Response message containing the new lease of the IPv6 address/prefix. After receiving the DHCPv6 Response message from the server, the client renews the lease of its IPv6 address/prefix.

    • When the link to which the DHCPv6 client is connected changes, the client needs to check whether its IPv6 address/prefix is still available.

      When the link to which the DHCPv6 client is connected changes, for example, the network cable is loosely connected, the client needs to send a DHCPv6 Confirm message to the server to check whether its IPv6 address/prefix is still available.

      If the IPv6 address needs to be validated, the client multicasts a DHCPv6 Confirm message containing the IPv6 address to be validated.

      After the DHCPv6 server receives the DHCPv6 Confirm message, if the IPv6 address/prefix assigned to the client is still available, the server replies with a DHCPv6 Response message in which the status of the IPv6 address is set to Success. After receiving the DHCPv6 Response message from the server, the client continues to use this IPv6 address.

      If the IPv6 prefix needs to be validated, the client multicasts a DHCPv6 Rebind message containing the IPv6 prefix to be validated. The DHCPv6 server processes the received Rebind message and then replies with a Response message. After the client receives the Response message from the server, if the lifetime of the IPv6 prefix is not 0, the client continues to use this prefix and renew the lease.

    • The DHCPv6 client detects a duplicate IPv6 address.

      If the DHCPv6 client detects a duplicate IPv6 address, it notifies the server of the address conflict.

      That is, the DHCPv6 client sends a DHCPv6 Decline message containing the duplicate IPv6 address to the server. The source address of the Decline message cannot be the duplicate address. If the client and server support unicast, the client unicasts a DHCPv6 Decline message to the server. Otherwise, the client multicasts a DHCPv6 Decline message to the server.

      When receiving the DHCPv6 Decline message, the server marks the IPv6 address contained in the Decline message as a duplicate address.

      NOTE:
      If the DHCPv6 server and DHCPv6 client are not on the same network segment, address conflicts cannot be detected.
    • The DHCPv6 client releases an IPv6 address/prefix.

      To release its IPv6 address/prefix, the DHCPv6 client sends a DHCPv6 Release message containing the IPv6 address/prefix to be released to the server. If the client and server support unicast, the client unicasts a DHCPv6 Release message. Otherwise, the client multicasts a DHCPv6 Release message.

      After receiving the DHCPv6 Release message from the client, the server releases the IPv6 address/prefix assigned to the client and responds with a Reply message.

  • Lease of an IPv6 prefix pool

    Different IPv6 prefix pools can be set with different leases by DHCPv6 servers, but prefixes in one prefix pool have the same lease.

  • Ability to parse options

  • Lease time of an IPv6 prefix pool

    The DHCPv6 server specifies different lease times for different IPv6 prefix pools. All the prefixes in a DHCPv6 prefix pool have the same lease time.

  • Renew time and rebind time of an IPv6 address pool

    In different IPv6 address pools, the respective proportions of the renew time and rebind time in the preferred lifetime can be set to different values. In one IPv6 address pool, the respective proportions of the renew time and rebind time in the preferred lifetime are fixed.

Download
Updated: 2019-01-02

Document ID: EDOC1100058415

Views: 12193

Downloads: 8

Average rating:
This Document Applies to these Products
Related Documents
Related Version
Share
Previous Next