The BRAS manages addresses through an address pool, including assigning and renewing address resources, reclaiming the assigned DNS addresses, and providing a Layer 3 interface (gateway) for access users.
Local address pool
The BRAS manages local address pools, including assigning, renewing, and reclaiming IP address resources in an address pool.
Remote address pool
A remote address pool maps to an external DHCP/BOOTP server. The remote address pool is not configured with actual IP addresses but merely specifies the DHCP/BOOTP server to which it maps. When a remote address pool is used, the BRAS can act as an agent to initiate or relay user requests to the DHCP/BOOTP server for address application, lease renewal, or address release.
When one or more addresses in an IP address pool cannot be used, you can configure protection for the address pool using any of the following four methods:
Locking an address pool
An address pool can be locked using a command. IP addresses in a locked address pool cannot be assigned any more. This method is usually used when an address pool cannot be deleted because an address in the pool is already used by an online user. In this case, lock the address pool so that no address can be assigned from this address pool. After all users go offline and all IP addresses in the address pool are released, delete the address pool.
Excluding IP addresses
In complex network planning, some IP addresses may need to be disabled.
Setting the IP address conflict flag
When an IP address in an address pool conflicts with a device's IP address, the status of this IP address can be set to conflicting using the corresponding command. After the conflict is cleared, the conflict flag can be reset manually.
Reclaiming IP addresses
When an IP address in an address pool is abnormal, that is, the IP address is in use but actually no user is using it, this IP address cannot be used any more. In this case, you can run a command to forcibly reclaim the IP address.
If a user fails to apply for an address from an IPv4 address pool for a specified number of times, this address pool is considered faulty and will be automatically isolated. The device then preferentially selects another available address pool for address assignment. If no other address pool is available, the device assigns the user an IP address from the current address pool.
The BRAS uses address leases to manage the validity period of users' IPv4 addresses. If the lease of a user's IP address expires and the user still wants to use this address, the user needs to apply for a lease renewal which is performed automatically. Lease renewal can be successful as long as this IP address is valid.
Address lease management works in either of the following ways:
If an IP address is assigned through a built-in DHCP client, the BRAS periodically scans the address. If the IP address lease of the DHCP client reaches 1/2 or 7/8 of the address lease, the DHCP client sends a DHCP request packet to renew the IP address lease.
If an IP address is assigned through a built-in DHCP server, the BRAS renews the IP address lease or reclaims the IP address after receiving a DHCP request packet from the DHCP client for address renewal.
Leased-based reservation: An IP address is dynamically assigned to a client. After the client goes offline, the IP address remains bound to the client and is deleted only after the address lease expires. Before the IP address is deleted, it is available only to the client it is bound.
When one MAC address maps to multiple sessions, IPoE users are identified based on the MAC address, access interface, and access VLAN of the client. When a client goes online for the first time, an IP address is dynamically assigned to the client.
After a delay for releasing IP addresses is configured, when PPP, L2TP, or DHCP users go offline, their IP addresses are in the delayed release state and cannot be assigned to new access users. After the configured delay elapses, the IP addresses are switched to the idle state and can be assigned to new users.
The delayed release function applies to local address pools, local rui-slave address pools, and DAP address pools.
After the user who is assigned a statically bound address, a reserved address, a static user address, or an address delivered by the RADIUS server goes offline, the original service process is retained and is not affected by the delayed release function.
VPN instances can be configured for address pools. The IP addresses of address pools in different VPN instances can overlap each other.
When a user goes online, an address pool needs to be selected from the address pool list bound to the user domain for address assignment.
Currently, there are many address pool selection policies. By default, the local address pool is selected before the remote address pool. You can configure the remote address pool to be selected before the local address pool in a domain. In NAT scenarios, you can configure a policy to preferentially assign public IP addresses from the local address pool and then from the remote address pool. In this manner, if both the local and remote address pools are available in the public address pool, the local public address pool is preferentially selected. If no public address pool is available, the device selects a private address pool. The local private address pool is preferentially selected over the remote private address pool. Multiple local address pools are assigned based on the sequence in which they were configured. Multiple remote address pools are selected based on the number of response failures of the DHCP server. The smaller the number of response failures of the DHCP server, the higher the priority.
For DHCP access users, an address pool can also be selected based on Option 60. If Option 60 does not match any address pool, other policies can be selected for address pool selection.