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Cisco Bug: CSCvu10863 - Cat4K/3.11.2- Multicast traffic being punted to CPU continuously after new mroute install/reload/SSO

Last Modified

Jul 25, 2020

Products (1)

  • Cisco Catalyst 4000 Series Switches

Known Affected Releases


Description (partial)

Cat4K VSS- issue is specific to 3.11.1 and 3.11.2 . It is not seen on 3.11.0.

Issue is seen with both default/global VRF and VRF-lite. 

After upgrading to 3.11.1 /3.11.2, we see that multicast feed is being punted to CPU continuously- not all packets of all flows but few packets for all flows. If there are multiple S,G groups (say 100), that is enough to hog CPU as much as 99%. 

We do see HW switched counters incrementing fine in MFIB, however hardware mroute programming indicates "Cpu aggport" for incoming Vlan interface (where feed came from) which is punting a few packets to CPU and this behavior needs to be corrected in software. 

Clearing mroute fixes the issue but it eventually comes back after reload/SSO.

If a new mroute is programmed, then also it exhibits same behavior for that group until that entry is cleared manually once. 

LAN_4500X# sh pl hard ip route multicast | sec
008196: v4 --> vrf: vrf_PROD (4)
        adjStats: true  fwdSel: 3  Dug: 0  mrpf: 300 (FwdToCpu)  fwdIdx: 0  ts: 0
        retIndex: 49150 retTs: 177489
            Vlan: 300  BridgeOnly: Y Te1/1/1(56) 
            Vlan: 300  BridgeOnly: Y Cpu aggport(6)  <<< uwanted and indicates this issue

LAB-4500X#sh pl cpu packet statistics | in L3 Fwd
L3 Fwd                           10080        87        56        17          0
LAB-4500X#sh pl cpu packet statistics | in L3 Fwd
L3 Fwd                           10688        81        57        17          0 << keeps growing at high rate

(*,, 00:05:21/00:02:32, RP, flags: SJCF
  Incoming interface: Null, RPF nbr
  Outgoing interface list:
    Vlan300, Forward/Sparse, 00:04:07/00:01:54
    Vlan1011, Forward/Sparse, 00:05:21/00:02:32

(,, 00:04:47/00:02:43, flags: FT
  Incoming interface: Vlan300, RPF nbr
  Outgoing interface list:
    Vlan1011, Forward/Sparse, 00:00:57/00:02:32

 (*, Flags: C HW
   SW Forwarding: 0/0/0/0, Other: 0/0/0
   Tunnel2 Flags: A
 (, Flags: HW
   SW Forwarding: 2/0/46/0, Other: 2705/0/2705
   HW Forwarding:   9498800/329924/46/124454, Other: 0/0/0
   Vlan300 Flags: A


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