BugZero | Cisco BugID CSCvt51424 - Local Microloop avoidance is overridden after loca...

Cisco - Defect ID: CSCvt51424

Local Microloop avoidance is overridden after local link down event

Cisco - Defect ID: CSCvt51424

Local Microloop avoidance is overridden after local link down event

Last updated on April 2nd, 2023

BugZero Risk Score
6.1 Medium

Overall: 6.1

Severity: 6.4

Lifecycle: 9.1

Popularity: 4.6

What is the BugZero Risk Score?

Cisco Integration

Learn more about where this data comes from

Cisco Integration

Learn more

Bug Scrub Advisor

Streamline upgrades with automated vendor bug scrubs

Bug Scrub Advisor

Learn more

BugZero Enterprise

Wish you caught this bug sooner? Get proactive today.

BugZero Enterprise

Learn more

Bug Details

Views: 2

Description

Symptom

ISIS microloop avoidance is not triggered by local link or BFD down event.

Conditions

The problem happens under specific timing conditions, when updated LSP triggers SPF prior the link or BFD down event is locally detected. The problem is more likely to happen under following conditions: - extremely aggressive initial LSP generation and SPF timers (example - both set to 1 ms) - event happening on remote side (interface shutdown etc), and slow local failure detection (copper interfaces, subinterfaces with slow BFD, L1/L2 infrastructure in between routers, etc)

Workaround

1/ Avoid using aggressive LSP and SPF timers 2/ Use "microloop avoidance segment-routing", which is more advanced solution with following benefits: - works for both local and remote (not directly connected) links - supports more triggers - link down, link up, metric change, overload bit set/clear - has more advanced detection mechanism to ignore LSP changes that do not affect the topology

Further Problem Description

This fix doesn't cover the case when SPF is first triggered by remote LSP change without receiving the local trigger. For regular microloop avoidance, the local trigger (interface or BFD down) must be received prior the SPF is started. Otherwise the FRR backup paths are not activated in the hardware, and delaying the RIB update would just slow down the network convergence. If this case needs to be covered, use segment-routing microloop avoidance.

Change history

2023-04-02 Added: 6.7.2, 6.7.3, 6.7.35, 6.7.4, 6.8.1, 6.8.2, 6.9.1, 6.9.2, 7.0.14, 7.1.2, 7.1.25, 7.1.3, 7.2.1, 7.2.12, 7.2.2, 7.3.0, 7.3.1, 7.3.15, 7.3.16, 7.3.2, 7.3.25, 7.3.26, 7.3.27, 7.3.3, 7.3.4, 7.4.1, 7.4.15, 7.4.16, 7.4.2, 7.5.1, 7.5.12, 7.5.2, 7.5.3, 7.5.4

Relevant Products

Click on a version to see all relevant bugs

Affected versions:No known affected versions

Fixed versions: 6.7.2, 6.7.3, 6.7.35, 6.7.4, 6.8.1, 6.8.2, 6.9.1, 6.9.2, 7.0.14, 7.1.2, 7.1.25, 7.1.3, 7.2.1, 7.2.12, 7.2.2, 7.3.0, 7.3.1, 7.3.15, 7.3.16, 7.3.2, 7.3.25, 7.3.26, 7.3.27, 7.3.3, 7.3.4, 7.4.1, 7.4.15, 7.4.16, 7.4.2, 7.5.1, 7.5.12, 7.5.2, 7.5.3, 7.5.4

Relevant Products

Click on a version to see all relevant bugs

Affected versions:No known affected versions

Top Cisco Defects

9.7Defect ID: CSCwk61938
ISE Evaluate OpenSSH CVE-2024-6387 "regreSSHion"
9.7Defect ID: CSCwa70008
Expired certs cause Security Intelligence updates to fail
9.7Defect ID: CSCwc94466
Cisco ASA/FTD Firepower 2100 SSL/TLS Denial of Service Vulnerability
9.7Defect ID: CSCun66310
Nexus 5596: System fails to boot after a power cycle
9.7Defect ID: CSCvq12070
Not able to establish more than 2 simultaneous ASDM sessions

Ready to prevent the next vendor outage?

Get a demo

Cisco - Defect ID: CSCvt51424

Local Microloop avoidance is overridden after local link down event

Cisco - Defect ID: CSCvt51424

Local Microloop avoidance is overridden after local link down event

Last updated on April 2nd, 2023

BugZero Risk Score6.1 Medium

Bug Details

Symptom

Conditions

Workaround

Further Problem Description

Top Cisco Defects

Ready to prevent the next vendor outage?

Links

BugZero Risk Score
6.1 Medium