Network operators are sometimes unable to turn on debug to troubleshoot customers issues on a live production network. Turning on debug may affect the BNG performance, and some support technicians may not have access to debug and configuration commands.
The show subscriber-mgmt errors command is a show command that captures detailed ESM errors. This command helps diagnose problems immediately without the need to turn on the debug function. Only DHCPv4 and PPPv4 supports this command; some support details are provided below. This command does not compromise the BNG performance and does not require debug or configuration commands.
DHCPv4 support:
dropped protocol messages (host setup/renew)
protocol timeouts
PPPoEv4 support:
dropped protocol messages
traps
IPv6 host setup errors may be captured in error logs.
All subscriber problems are first stored in a main circular buffer. The main circular buffer is then fed into smaller circular buffers, organized by MAC addresses. When the buffer is full, the first circular buffer purges the oldest message to make room for the newest message. The smaller circular buffers (one per MAC address) store a limited number of messages per MAC. Again, the smaller buffer deletes the oldest to make room for the newest. The circular buffer, per MAC, prevents one device from holding all the error messages in the buffer. The main circular buffer can hold 5,000 errors in total, while the smaller buffer can hold 10 log entries per MAC. The circular buffer supports CPM3 and higher.
The show command allows sorting by MAC, subscriber SAP, SDP, and unknown-origin (unknown SAP or SDP). The show command allows the input of a specific MAC, SAP, or SDP to directly search for particular subscriber issues or problems.
The circular buffer only logs drop reasons for DHCPv4 and PPPoEv4. Non-error reasons are never logged; for example, a drop because of being in SRRP standby is not logged. The circular buffer has a timestamp associated with each error and the errors are listed beginning with the most recent. Error logs are lost on a HA switchover, and persistency is not supported. There is no throttling mechanism for the same errors; it is possible to fill the circular buffer with the same error message from different MAC addresses.