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Cisco Bug: CSCuw30290 - Delay the backup path installation for bundle Convergence issue

Last Modified

Sep 20, 2018

Products (8)

  • Cisco ASR 9000 Series Aggregation Services Routers
  • Cisco ASR 9922 Router
  • Cisco IOS XR Software
  • Cisco ASR 9010 Router
  • Cisco ASR 9904 Router
  • Cisco ASR 9006 Router
  • Cisco ASR 9001 Router
  • Cisco ASR 9912 Router

Known Affected Releases

5.3.2.BASE

Description (partial)

We have mixed family of line cards. The Tomahawk LCs are faster than the
Typhoon LCs. This is causing the programming (convergence) on the Typhoon LC
to take longer compared to the Tomahawk LC
• So in the interim we have state where Ingress Tomahawk LC is programmed to
switch from Bundle 1 to Bundle 2. The packet goes to the Typhoon LC which is part
of Bundle 2 but since this card is not yet programmed it black holes the traffic.
• NHID feature is present on the platform to address such cases where we have
speed mismatched cards. If we have LFA enabled NHID is not supported currently.
• LSNT team has verified with LFA configuration (NHID enabled) removed we are not
seeing such high traffic loss.
• Code changes for LFA to utilize NHID would need additional packet buffer header
memory.
• Typhoon does not have the additional space to support this.
• Tomahawk would need microcode work in forwarding.

Symptom:
Packet loss of 10-15 sec on some streams during traffic move from Tomahawk
Only Mixed Bundle (B1) to Typhoon/Tomahawk Mixed Bundle (B2), without LFA
FRR being triggered.

Conditions:
Convergence event without LFA trigger
• Bundle 1 is not going down due to triggers (listed below).
• Ingress LC is Tomahawk LC/Typhoon (Mod-80) and egress is Typhoon LC
(24x10GE LC)

Following are the triggers:
• OSPF link manual costing out of Bundle 1.
• Shutting of some member links of the bundle 1 which trigger OSPF cost
threshold (BW <40GE).
• LDP failure on Bundle 2. (Seen when traffic re-convergence to Bundle-2)
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Bug Details Include

  • Full Description (including symptoms, conditions and workarounds)
  • Status
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