[c-nsp] 3750 acting as a hub - resolved

[Ed Butler]

I went through all the config changes that were made, and there was
absolutely nothing that would have had this kind of affect that I can
see.

As an aside, a packet capture showed over half the packets had no data,
eg 66 byte TCP packets. The problem righted itself after issuing a
"clear mac-address-table dynamic" command. Why it happened in the first
place is still a mystery to me, I would be interested to hear any
thoughts.

Regards,

Ed Butler
RapidSwitch Ltd
DDI: 020 7106 0731

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

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-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Ed Butler
Sent: 02 April 2007 16:20
To: nsp
Subject: Re: [c-nsp] 3750 acting as a hub

To reply to myself - just had an idiot moment. This is happening on
other VLANs too on the switch, and started happening at some minor
maintenance we made. Going to compare the before/after config to see
what could cause the odd behaviour; I can't immediately thing of changes
that would facilitate this.

Regards,

Ed Butler
RapidSwitch Ltd
DDI: 020 7106 0731

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

This email message is intended only for the addressee(s) and contains
information that may be confidential and/or copyright.  No
representation is made that this email or any attachments are free of
viruses. Virus scanning is recommended and is the responsibility of the
recipient. RapidSwitch Ltd is registered in England & Wales Company No.
04535693, Registered Address: 3 Beacon Mews, South Road, Weybridge, KT13
9DZ. VAT Registration No. GB 794 3811 96. All prices exclude VAT unless
otherwise stated. Quotations valid for seven days.
-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Ed Butler
Sent: 02 April 2007 16:11
To: nsp
Subject: [c-nsp] 3750 acting as a hub

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

This email message is intended only for the addressee(s) and contains
information that may be confidential and/or copyright.  No
representation is made that this email or any attachments are free of
viruses. Virus scanning is recommended and is the responsibility of the
recipient. RapidSwitch Ltd is registered in England & Wales Company No.
04535693, Registered Address: 3 Beacon Mews, South Road, Weybridge, KT13
9DZ. VAT Registration No. GB 794 3811 96. All prices exclude VAT unless
otherwise stated. Quotations valid for seven days.

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