[c-nsp] 3750 acting as a hub

[Ed Butler]

We saw a surge in incoming traffic to a number of boxes on a certain
VLAN on a 3750 stack earlier. The traffic appeared to be unicast traffic
to a number of different boxes on the VLAN, but it was being broadcast
to everything on that port - eg normal hub behaviour. This doesn't
happen to other VLANs on the same box, and there's no apparent reason
for the behaviour.

Cisco 3750 stack running on 12.2(25)SED1. 

1. No spanning tree issues:

3750#sh spanning-tree vlan 400 detail  | in last  
  Number of topology changes 79 last change occurred 17:09:44 ago


2. TCAM space looks fine:

3750#sh ip arp sum
3353 IP ARP entries, with 149 of them incomplete

3750#sh sdm pref
 The current template is "desktop default" template.
 The selected template optimizes the resources in
 the switch to support this level of features for
 8 routed interfaces and 1024 VLANs. 

  number of unicast mac addresses:                  6K
  number of IPv4 IGMP groups + multicast routes:    1K
  number of IPv4 unicast routes:                    8K
    number of directly-connected IPv4 hosts:        6K
    number of indirect IPv4 routes:                 2K
  number of IPv4 policy based routing aces:         0
  number of IPv4/MAC qos aces:                      512
  number of IPv4/MAC security aces:                 1K
 
3750#sh mac-address-table count vlan 400

Mac Entries for Vlan 400:
---------------------------
Dynamic Address Count  : 77
Static  Address Count  : 0
Total Mac Addresses    : 77

Total Mac Address Space Available: 2680

Regards,

Ed Butler
RapidSwitch Ltd
DDI: 020 7106 0731

RapidSwitch Ltd, Sovereign House, 227 Marsh Wall, London, E14 9SD

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