cdp neighbor downstream connections

[lcaruso]

Hi,

I'm trying to use sh cdp neighbor as a first pass to track down briding loops in a network. It is showing me the following: switch 1-1 has a connection to the hp procurve via port fas1 and it has a connection to switch 2-1 via port fas1, the same port.

Can I correctly conclude that the first reported connection to the hp procurve is the actual physical connection via port fas1 and the second connection, also via port fas1, is downstream from the first connection? Thanks.

s-1-1#sh
cdp ne

Capability
Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

                 
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone, 

                  D
- Remote, C - CVTA, M - Two-port Mac Relay 

Device
ID        Local
Intrfce     Holdtme    Capability 
Platform  Port ID

hp procurve 2524(3rd flr)(000883-2cc900)

                
Fas 1/0/1        
148              
S    HP 2524   18

s-2-1.client.org

                
Gig 1/0/2        
168             
S I   WS-C3750- Gig 1/0/1

s-2-1.client.org

                
Fas 1/0/1        
156             
S I   WS-C3750- Fas 1/0/1

s-3-1.client.org

                
Gig 1/0/1        
143             
S I   WS-C3750- Gig 1/0/1

[Eugene Lau · Accepted solution]

Hi there,

Did a quick google and found that HP2524 supports CDP

http://61-218-49-2.hinet-ip.hinet.net/network/L2/HP/2524%202512/2524and2512_spec_en.pdf

Technically speaking, if the HP2524 understands CDP, then it "shouldn't" flood the CDP Frame. In the old days, when Cisco switches were connected to other vendors switches that did not support CDP, you could see multiple Cisco switches connected to fa1/0/1.

I would assume one of two things:

1. HP2524 is flooding the CDPv2 frame but understands the HP2524 CDP (not sure if it's v1 or v2)

2. There's another switch in the middle that does not understand CDP

3750 fa1/0/1 ----- switch ----HP

                            |___ cisco

S-2-1 seems to have a Gig and Fa connection back to the 3750, possibly for some type of redundancy. If you don't see any blocked ports in that path, you could shut the fa link down to break any possible loops.

HTH

Eugene

[lcaruso]

Thanks for your reply!  There very well could be another switch inbetween, or these HP's 2524's are so old they don't understand the CDP being used by the 3750 running the latest 12.2(55). I'm trying to figure out as much as I can before I start toning cable runs. Thanks again.