Description

This article describes a scenario when subscribers are not able to connect and "please modify address allocation scheme to avoid subscriber failures" syslog messages are continuously generated. 

Symptoms

The following syslog messages indicate that subscribers are not able to connect due to address allocation failures: 
<date> <time> <device> authd[63299]: %DAEMON-3: Address Pool <name> is in maintenance mode "hold-down" is set.
<date> <time> <device> authd[63299]: %DAEMON-3: please modify address allocation scheme to avoid subscriber failures
<date> <time> <device> authd[63299]: %DAEMON-3: Address Pool <name> is in maintenance mode "hold-down" is set.
<date> <time> <device> authd[63299]: %DAEMON-3: please modify address allocation scheme to avoid subscriber failures

Solution

These syslog messages provide clear indication that authentication daemon is not able to allocate addresses from an address pool due to active-drain configuration for this pool. This command is used to prevent address allocation from an address pool, usually in preparation for deletion of this pool, but it's expected that addresses in other pools should be available. If authentication daemon is not able to find any available addresses and an address pool is configured in active-drain mode, the error message mentioned above is generated to notify operator that the system is not able to allocate addresses and subscribers are not able to connect.

An excerpt from Configuring DHCP Local Address Pool Rapid Drain: 
You can force the DHCP local server to stop allocating addresses from a
specific local address pool by configuring the pool to active-drain mode. This
mode enables the server to gracefully terminate subscribers that are already
using addresses assigned from that pool and transition them to another pool.
When a DHCP subscriber attempts to renew (at the T1 renewal time) the lease on
an IP address from a pool now configured for active-drain mode, the DHCP local
server replies with a NAK to the subscriber’s renewal request. This response
forces the subscriber to renegotiate a lease. The server then allocates a new
IP address from an alternative address pool that is not configured for active
drain.

Modification History

2024-03-08 : Article Created

Related Information

Address-Assignment Pools for Subscriber Management