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New Member

Too many devices on VLAN?

Can anyone recommend counters, logs or specific Sniffer captures that can be viewed or captured to tell if excessive broadcasts or multicasts may be causing trouble in my environment. I currently have approximately 500 devices running on a single network, my native vlan, vlan1. Is there anything besides broadcasts or multicasts that could adversely affect performance on a single VLAN?

My environment:

- 6509 in MDF

- GIG fiber from MDF to 14 IDF's that contain Catalyst 3500's and 2950's

- IDF's typically contain several switches that use gigastack modules

- Single NT 4 Domain with several w2k servers.

- Pure TCP/IP environment, no IPX or Appletalk

- Workstations all pulling DHCP from MS DHCP server

- Approximately 100 CAD workstations using PRO E, remainder of workstions using a variety of apps that include Oracle, Windchill and 3270 mainframe emulation.Oracle, Windchill and mainframe (3270) hosts all reside off site. DNS servers reside off site.

- Approximately 23 Cisco 1200 AP's with dozens of aironet clients and Cisco workgroup bridges. All reside on native VLAN

- All workstations and severs running Norton anti virus pulling dats from a local Norton primary server

We have run a single vlan for several years with no apparent problems but I am starting to wonder if this may be a problem especially relating to anomalies that I see with wireless clients.

Thanks in advance for any help....

New Member

Re: Too many devices on VLAN?

I'm fairly certain that you know more about the technicals as a whole than I do, but I'd recommend moving everything OFF of your native VLAN and leaving the native VLAN as your backbone trunk network between only switching/routing devices.

If you use SNMP to manage the network, that would be on the native VLAN also.

Of course, breaking your network up into more VLANs would further reduce broadcast/multicast traffic also.

New Member

Re: Too many devices on VLAN?

Yikes, your network sounds just like ours ! At one point we would have had upwards of 1000 users (NT/W2K, some XP) in a single VLAN. Our ambient broadcast level was about 60Kbps, which was not a bother 99% of the time. Browser wars tended to increase that level from time to time, and sometimes this caused some performance grief at lower bandwidth remote sites, but only a little. Another time a machine was arping many times a second (due to a stupid popup or spyware) and that also caused some slow speed line problems. Generally though we do not have any significant performance problems.

Now that I think about it, we must have close to 500 devices now in one VLAN, and it works fine (with about 30Kbps ambient traffic).


New Member

Re: Too many devices on VLAN?

Can you please tell me how you derived the figure for your ambient broadcast level?

Re: Too many devices on VLAN?

You need a minimum of 3 vlans, Network Management, Wired, and Wireless.