On regular group interfaces, redundancy is supported by enabling SRRP and IPoE session stateless redundancy. For more information about stateless redundancy, see Stateful Multi-Chassis Redundancy (MCS). The backup router is always in the backup-routing mode. There is no support for shunting traffic via a redundant interface from the standby to the active router.
IPv6 traffic and public IPv4 is attracted to the correct active (SRRP master state) router by the regular track-SRRP mechanism. L2-Aware NAT outside pools cannot use track-SRRP and should be configured distinctly on both routers making up the redundant pair. After a redundancy event, each home gains a new outside IP address on the new active router.
BRGs send out Gratuitous ARP (GARP) messages, which direct traffic to the correct active router. These GARPs update the FDB of the dual-homed Layer 2 aggregation nodes. GARPs are not supported for L2-Aware inside prefixes. At least one subscriber interface subnet must be explicitly configured to send a GARP.
When using MSAP deployments, the managed SAPs are not synchronized and must be recreated on the new active router via data-triggered authentication. Because there are no managed SAPs present, no GARPs can be sent when a standby router becomes active. If the aggregation node has a shared FDB for all C-VLANs (FDB per S-VLAN) or for all S-VLANs (FDB per switch), it is recommended to configure a single static SAP per S-VLAN or per port over which a single ARP can be sent.