Stateless redundancy uses SRRP in the same form as the current implementation for active and standby selection and peer liveness detection, but does not need subscriber state synchronization using MCS that requires CPM/IOM resources to be on standby node.
Stateless redundancy has the following characteristics:
IPoE sessions and their hosts (DHCP,DHCP6,SLAAC, and DT) are not synchronized by the subscriber management IPoE MCS client.
SRRP is synchronized over MCS.
Active BNG in the (SRRP master state) only processes the data-trigger and authenticates and creates a subscriber host state.
Standby BNG in the (SRRP non-master state) discards all upstream packets.
Shunt and redundant interfaces are not supported.
After an SRRP switchover, the new active BNG starts processing subscriber traffic. The previous active BNG deletes all IPoE sessions and IPoE subscriber hosts on an SRRP switchover. Accounting stops are sent to indicate that this node became standby (non-master SRRP state). Accounting messages are different based on the radius-accounting-policy configuration.
queue-instance-accounting:
accounting-stop with Alc-Error-Code = Node has switched to stateless backup
session-accounting:
interim-update with Alc-Acct-Triggered-Reason = Node has switched to stateless backup, upon each stack deletion if host-update is configured, and accounting-stop with Alc-Error-Code = Node has switched to stateless backup
accounting:
accounting-stop with Alc-Error-Code = Node has switched to stateless backup, upon each host deletion
The DHCP local server state can be synchronized for DHCP promotion.
DHCP promotion for BRG requires lease state synchronization between redundant BNGs, which disables protocol-triggered IPoE ESM without an IPoE session. This requires the config>service>ies | vprn>sub-if>grp-if>ipoe-session>stateless-redundancy command to be configured.
host-PPPoE (PTA and LAC) processing can be tied with an SRRP instance for stateless redundancy. Only the active BNG (SRRP master state) processes PPPoE/PPP control plane data. A standby BNG (SRRP non-master state) does not send LCP echo messages. After switchover, subscriber hosts retry to connect after echo timeout.
Supports both static SAP and MSAP.
Figure: Stateless multi-chassis redundancy shows an example of stateless multi-chassis redundancy.
