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Configuration Guide - IP Service

CloudEngine 8800, 7800, 6800, and 5800 V200R003C00

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 Server Allowing DHCPv6 Clients to Renew Address Leases

DHCPv6 Server Allowing DHCPv6 Clients to Renew Address Leases

IPv6 addresses that are dynamically allocated by a DHCPv6 server have leases. An IPv6 address application message from a DHCPv6 client can carry an expected lease. When allocating network configuration parameters, the DHCPv6 server compares the expected lease with the specified lease in the address pool and allocates the IPv6 address with a smaller lease to the DHCPv6 client. When the lease expires, the DHCPv6 server reclaims the IPv6 address, which can then be allocated to another client. This mechanism improves IPv6 address utilization and releases IPv6 addresses after clients get offline. If the DHCPv6 client wants to keep using this IPv6 address when the lease is going to expire, the DHCPv6 client needs to renew the IPv6 address lease.

The following describes how a DHCPv6 client renews the IPv6 address lease with and without a DHCPv6 relay agent.

Address Lease Renewal (Without a Relay Agent)

Figure 8-10 Address lease renewal (without a relay agent)

  1. When the lease reaches T1 (indicating 50% of the lifetime by default), the DHCPv6 client sends a unicast Renew message (carrying the DHCPv6 server's DUID) to the DHCPv6 server that allocates the IPv6 address to request for lease renewal.
  2. After receiving the Renew message, the DHCPv6 server checks the IPv6 address carried in the message. If the check passes, the DHCPv6 server replies with a Reply message carrying the IPv6 address with a new lifetime, T1', and T2' to the DHCPv6 client.
  3. If the DHCPv6 client receives the Reply message, the IPv6 address lease is successfully renewed (counted from 0).
  4. If no reply is received from the DHCPv6 server when the lease reaches T2 (indicating 80% of the lifetime by default), the DHCPv6 client sends a multicast Rebind message to all DHCPv6 servers on the same link to request for IPv6 address lease renewal.
  5. When a DHCPv6 server receives the Rebind message, the DHCPv6 server checks the DHCPv6 server DUID carried in the message.
    • If the DHCPv6 server DUID carried in the Rebind message is not the DHCPv6 server's DUID, the DHCPv6 server does not respond to the Rebind message.
    • If the DHCPv6 server DUID carried in the Rebind message is the DHCPv6 server's DUID, the DHCPv6 server checks the IPv6 address carried in the message. If the check passes, the DHCPv6 server replies with a Reply message carrying the IPv6 address with a new lifetime, T1', and T2' to the DHCPv6 client.
  6. If the DHCPv6 client receives the Reply message, the IPv6 address lease is successfully renewed (counted from 0). If the Reply message is not received, the DHCPv6 client stops using the current IPv6 address when the IPv6 address lease expires and sends a Solicit message to request for a new IPv6 address.

Address Lease Renewal (with a Relay Agent)

Figure 8-11 Address lease renewal (with a relay agent)

  1. When the lease reaches T1 (indicating 50% of the lifetime by default), the DHCPv6 client sends a unicast Renew message (carrying the DHCPv6 server's DUID) to the DHCPv6 server that allocates the IPv6 address to request for lease renewal.
  2. After receiving the Renew message, the DHCPv6 server checks the IPv6 address. If the check passes, the DHCPv6 server replies with a Reply message carrying the IPv6 address with a new lifetime, T1', and T2' to the DHCPv6 client.
  3. If the DHCPv6 client receives the Reply message, the IPv6 address lease is successfully renewed (counted from 0).
  4. If no response is received from the DHCPv6 server when the lease reaches T2 (indicating 80% of the lifetime by default), the DHCPv6 client sends a multicast Rebind message to the DHCPv6 relay agent. The DHCPv6 relay agent then sends a unicast Relay-forward message to the DHCPv6 server that allocates the IPv6 address to request for lease renewal. For details on how the DHCPv6 relay agent processes received messages, see Address and Network Configuration Parameter Allocation (with a Relay Agent).
  5. After receiving the Relay-forward message, the DHCPv6 server checks the IPv6 address. If the check passes, the DHCPv6 server replies with a Relay-reply message carrying the IPv6 address with a new lifetime, T1', and T2' to the DHCPv6 relay agent. After receiving the Relay-reply message, the DHCPv6 relay agent parses the new lifetime, T1', and T2' and sends the IPv6 address with the new lifetime, T1', and T2' to the DHCPv6 client through a Relay-reply message.
  6. If the DHCPv6 client receives the Reply message, the IPv6 address lease is successfully renewed (counted from 0). If the Reply message is not received, the DHCPv6 client stops using the current IPv6 address when the IPv6 address lease expires and sends a Solicit message to request for a new IPv6 address.
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Updated: 2019-05-08

Document ID: EDOC1100004354

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