65b2f968_R_12000_Series_Router____Cisco_ase_verbose_Field_Descriptions_Description
[Field] ATT/P/OL [Description] 
ATT—Attach bit. This bit indicates that the router is also a Level 2 router, and it can reach other areas. Level 1-only routers and Level 1-2 routers that have lost connection to other Level 2 routers use the Attach bit to find the closest Level 2 router. They point to a default route to the closest Level 2 router. P—P bit. Detects if the intermediate system is area partition repair capable. Cisco and other vendors do not support area partition repair. OL—Overload bit. Determines if the IS is congested. If the Overload bit is set, other routers do not use this system as a transit router when calculating routers. Only packets for destinations directly connected to the overloaded router are sent to this router.
Cisco IOS XR Routing Command Reference for the Cisco XR 12000 Series Router, Release 4.2.x - IS-IS Commands on Cisco IOS XR Software [Cisco XR 12000 Series Router] - Cisco