Cisco Bug: CSCvs75321 - ISIS and MRIB out of sync for the FTag oifs
Aug 28, 2020
- Cisco Nexus 9000 Series Switches
Known Affected Releases
Symptom: Broadcast Traffic/Unknown Unicast/multicast traversing the fabric can get blackholed on nodes that have inconsistent ISIS and MRIB states. ISIS Output for FTAG 0 node-1103 (vsh)# show isis internal mcast routes | more <snip> FTAG ID: 0 [Root] [Enabled] Cost:( 2/ 8/ 0) ---------------------------------- Root port: Ethernet1/2.47 OIF List: Ethernet1/5.12 Ethernet1/6.16 Ethernet1/13.24 Ethernet1/17.21 Ethernet1/19.37 Ethernet1/20.43 Ethernet1/22.23 Ethernet1/23.38 Ethernet1/24.41 Ethernet1/25.50 Ethernet1/33.33 Ethernet1/34.34 <snip> The MRIB outputs should include both the root port and the OIFs above aggregated into the "outgoing interface list" However below you see that root port e1/2 is missing in the outputs. In this scenario, the BUM traffic using FTAG 0 and ingressing port e1/2 gets dropped. Sideband ELAM will register a fwddrop=1 FTAG 0 MRIB output node-1103 (vsh)# show ip mroute detail vrf all | more <snip> (*, 0.64.0.0/32), FTAG Route: , FTAG Enable , uptime: 31w5d, isis(0) Data Created: No OTV Router Mode Stats: 0/0 [Packets/Bytes], 0.000 bps Incoming interface: Null, RPF nbr: 0.0.0.0 Outgoing interface list: (count: 12) Ethernet1/25.50, uptime: 1d00h Ethernet1/24.41, uptime: 1d00h Ethernet1/23.38, uptime: 1d00h Ethernet1/22.23, uptime: 1d00h Ethernet1/20.43, uptime: 1d00h Ethernet1/19.37, uptime: 1d00h Ethernet1/17.21, uptime: 1d00h Ethernet1/13.24, uptime: 1d00h Ethernet1/6.16, uptime: 1d00h Ethernet1/5.12, uptime: 1d00h Ethernet1/34.34, uptime: 4w5d Ethernet1/33.33, uptime: 4w5d <snip> Conditions: This issue occurs due to link flaps between leaf switches and spine switches or interDC links that may cause FTAG reconvergence, and ARP flood is enabled for the bridge domain.
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