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jwilliams31
Beginner

Find unmanaged switches connected to managed switches

I'm trying to create a network "map" for a network that has both managed and unmanaged switches.  Is there a way, while connected to one of the managed switches that I can find what port an unmanaged, possibly non-Cisco switch may be connected to?

1 ACCEPTED SOLUTION

Accepted Solutions
Seb Rupik
VIP Advisor

Hi there,

non-cisco devices *may* have LLDP enabled, which if configured on the connected cisco switch, will reveal its identity. If the mystery switch is not running a discovery protocol the only other way you might be able to know it is hanging off a switchport is to check the mac-address table on your cisco switch and look for switchports with a large number of MAC addresses.

 

cheers,

Seb.

View solution in original post

3 REPLIES 3
Seb Rupik
VIP Advisor

Hi there,

non-cisco devices *may* have LLDP enabled, which if configured on the connected cisco switch, will reveal its identity. If the mystery switch is not running a discovery protocol the only other way you might be able to know it is hanging off a switchport is to check the mac-address table on your cisco switch and look for switchports with a large number of MAC addresses.

 

cheers,

Seb.

hemmerling
Beginner

 Like the other post said "show cdp neighbor" "show lldp neighbor" should show you both cdp and lldp neighbors.
Only works for locally connected switches, but you can always look at the mac table (show mac address) and see which ports have more than one or two MACs on them (1 or 2 could just be a phone, 3+ should be hubs or switches).

 

Joseph W. Doherty
Hall of Fame Expert

Just to add to what the other posters have noted, an unmanaged switch, I believe, is more likely NOT to support CDP and/or LLDP.  So, as the other posters have already noted, possibly more than one MAC, or even more likely, more than two MACs on a port might indicate an unmanaged switch (or hub).  Of course, unfortunately, just one MAC doesn't mean there's not another device, like a switch, in-line.

With two MACs, the MACs, themselves, might provide a clue, as burnt-in MACs are globally unique and assigned (in blocks) to different vendors.  I.e. two MACs from the same PC company or two from the same VoIP company, might indicate as unmanaged switch.

Lastly, since an unmanaged switch may be "invisible", you might also face the issue there might be multiple such switches off a port.  The only clue for such might be "seeing" more than 24 or 48 MACs on a port.

Oh, also don't forget wireless bridges might be "invisible" on a port too.