Route And Label Consistency Checker - Cisco ASR 9000 Series Routing Configuration Manual

Implementing and Monitoring RIB
there is no damping on the oscillation, then both the protocol process and the RIB process have high CPU
use, affecting the rest of the system as well as blocking out other protocol and RIB operations. This problem
occurs when a particular combination of routes is received and installed in the RIB. This problem typically
happens as a result of a network misconfiguration. However, because the misconfiguration is across the
network, it is not possible to detect the problem at configuration time on any single router.
The quarantining mechanism detects mutually recursive routes and quarantines the last route that completes
the mutual recursion. The quarantined route is periodically evaluated to see if the mutual recursion has gone
away. If the recursion still exists, the route remains quarantined. If the recursion has gone away, the route is
released from its quarantine.
The following steps are used to quarantine a route:
1 RIB detects when a particular problematic path is installed.
2 RIB sends a notification to the protocol that installed the path.
3 When the protocol receives the quarantine notification about the problem route, it marks the route as being
"quarantined." If it is a BGP route, BGP does not advertise reachability for the route to its neighbors.
4 Periodically, RIB tests all its quarantined paths to see if they can now safely be installed (moved from
quarantined to "Ok to use" state). A notification is sent to the protocol to indicate that the path is now safe
to use.

Route and Label Consistency Checker

The Route Consistency Checker and Label Consistency Checker (RCC/LCC) are command-line tools that
can be used to verify consistency between control plane and data plane route and label programming in IOS
XR software.
Routers in production networks may end up in a state where the forwarding information does not match the
control plane information. Possible causes of this include fabric or transport failures between the Route
Processor (RP) and the line cards (LCs), or issues with the Forwarding Information Base (FIB). RCC/LCC
can be used to identify and provide detailed information about resultant inconsistencies between the control
plane and data plane. This information can be used to further investigate and diagnose the cause of forwarding
problems and traffic loss.
RCC/LCC can be run in two modes. It can be triggered from EXEC mode as an on-demand, one-time scan
(On-demand Scan) , or be configured to run at defined intervals in the background during normal router
operation (Background Scan). RCC compares the Routing Information Base (RIB) against the Forwarding
Information Base (FIB) while LCC compares the Label Switching Database (LSD) against the FIB. When an
inconsistency is detected, RCC/LCC output will identify the specific route or label and identify the type of
inconsistency detected as well as provide additional data that will assist with further troubleshooting.
RCC runs on the Route Processor. FIB checks for errors on the line card and forwards first the 20 error reports
to RCC. RCC receives error reports from all nodes, summarizes them (checks for exact match), and adds it
to two queues, soft or hard. Each queue has a limit of 1000 error reports and there is no prioritization in the
queue. RCC/LCC logs the same errors (exact match) from different nodes as one error. RCC/LCC compares
the errors based on prefix/label, version number, type of error, etc.
On-demand Scan
In On-demand Scan, user requests scan through the command line interface on a particular prefix in a particular
table or all the prefixes in the table. The scan is run immediately and the results are published right away.
LCC performs on-demand scan on the LSD, where as RCC performs it per VRF.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
Route and Label Consistency Checker
505