SHCV policies are used to control subscriber host connectivity verification which verifies the host connectivity to the BNG. There are two types of SHCV: periodic and event triggered. Before Release 13.0R4, some event triggered SHCV relied on the reference timer set by the host-connectivity-verify under the group interface while others had hard-coded values. Release 13.0R4 introduced the SHCV policy that allows individual configuration of trigger SHCV timers and periodic SHCV timers depending on the application.
Under the group-interface, the host-connectivity-verify configuration was used as a reference timer for some event triggered SHCV while other used hard-coded values. The SHCV policy separated out every type of SHCV and allows each type to have their individual configurable timer values. Furthermore, individual SHCV trigger types can be shut down. The SHCV policy can be applied to one or more group interfaces and can be configured differently for IPv4 vs. IPv6 hosts. There are various types of triggered SHCV:
ip-conflict
This SHCV is sent when a SAP detects that there is a IP address or prefix conflict on the SAP.
host-limit-exceeded
Sent when a subscriber has exceeded a configured host or session limit. Host limits are set in the sla-profile host-limits and in the sub-profile host-limits. Session limits are set in the group-interface ipoe-session sap-session-limit and session-limit, in the sla-profile session-limits and in the sub-profile session-limits contexts.
inactivity
The category-map configured under sla-profile can trigger an SHCV when the subscriber host becomes idle.
mobility
Intended for mobility applications such as Wi-Fi. When a subscriber moves between SAPs and requests for the same IP address, a triggered SHCV is sent to verify if the old host is still connected before removing the old host entry.
mac-learning
For IP-only static-host MAC learning. The trigger SHCV is sent to learn the subscriber MAC when a no shutdown command is executed on the CLI for the static host.
Some SHCVs are triggered based on a host’s DHCP messages. These DHCP messages are not buffered. The SHCV is used only to perform a verification check on an old host to verify if the host is still connected to the BNG. Therefore, the BNG still requires the new hosts to retransmit their DHCP messages after the SHCV removes the disconnected host.