Confusing CDP Neighbour command result.

parvees123 · ‎07-20-2005

Hai,

I am using 3550 in Distribution layer and 4000 series in the core layer. I have more than 12 switches in the distribution layer and those switches are connected to Core layer swicthes and dont have any direct connection.

I have checked the result of " sh cdp neighbour details" on one of my distribution switch. Its shwoing result like one gigabit port is connected to two different destinations. when i checked with one of the destination which was shown in the present DL switch , there also the same issue, its connected to two different ports. How this happens?, What could be the reason for this result. If a gigabit hub is there in picture, will this happen, coz i am very new to this topology , i am going through the configs, where i found this sort of result.?

Any idea what is the problem?

Regards

PSM

Richard Burts · ‎07-20-2005

I have experienced something that sounds somewhat similar to what you describe. I have done show cdp neighbor (or show cdp neighbor detail) and seen what appeared to be two devices connected where I knew that there was a single device connected. The explanation was that the device had been configured and the hostname changed. For a period of time (depending on the cdp hold timer) cdp has both the old name and the new name.

Perhaps this is what you were seeing? Is there any chance that a device name had been reconfigured? If not it would be helpful if you would post the output of show cdp neighbor detail so we can perhaps get a better understanding of what is going on.

HTH

Rick

HTH

Rick

parvees123 · ‎07-20-2005

Hi Rick,

Following is the Output .

-------------------------

Device ID: tel-3550-sel

Entry address(es):

IP address: 100.201.139.8

Platform: cisco WS-C3550-24-PWR, Capabilities: Switch IGMP

Interface: GigabitEthernet0/2, Port ID (outgoing port): GigabitEthernet0/1

Holdtime : 128 sec

Version :

Cisco Internetwork Operating System Software

IOS (tm) C3550 Software (C3550-I9Q3L2-M), Version 12.1(13)EA1a, RELEASE SOFTWARE

(fc1)

Compiled Tue 25-Mar-03 23:21 by yenanh

advertisement version: 2

Protocol Hello: OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=0000000

0FFFFFFFF010229FF000000000000000DEDA5AD00FF0000

VTP Management Domain: 'Zen'

Native VLAN: 1

Duplex: full

-------------------------

Device ID: tel-3550-Gel

Entry address(es):

IP address: 100.201.139.5

Platform: cisco WS-C3550-24-PWR, Capabilities: Switch IGMP

Interface: GigabitEthernet0/2, Port ID (outgoing port): GigabitEthernet0/1

Holdtime : 102 sec

Version :

Cisco Internetwork Operating System Software

IOS (tm) C3550 Software (C3550-I9Q3L2-M), Version 12.1(14)EA1a, RELEASE SOFTWARE

(fc1)

Compiled Tue 02-Sep-03 03:55 by antonino

advertisement version: 2

Protocol Hello: OUI=0x00000C, Protocol ID=0x0112; payload len=27, value=0000000

0FFFFFFFF010229FF000000000000000DBDF32380FF0000

VTP Management Domain: 'Zen'

Native VLAN: 1

Duplex: full

---------------------------------------------------------------------------------------------------

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

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

Device ID Local Intrfce Holdtme Capability Platform Port ID

tel-3550 Gig 0/2 178 S I WS-C3550-2Gig 0/1

tel-4506 Gig 0/1 147 R S I WS-C4506 Gig 2/5

tel-3550 Gig 0/2 79 S I WS-C3550-2Gig 0/1

tel-3550

-------------------------------------------------------------------------------------------

tel-3550 #sh cdp

Global CDP information:

Sending CDP packets every 60 seconds

Sending a holdtime value of 180 seconds

Sending CDPv2 advertisements is enabled

Regards

PSM

Kevin Dorrell · ‎07-20-2005

I wonder: are these devices connected with fiber links? Is there any chance that you could have some fibers mis-paired, tx vs. rx? Are you running UDLD?

Kevin Dorrell

Luxembourg

parvees123 · ‎07-20-2005

Hi Kevin,

Its a gigabit interfce and is connected with fibre only. UDLD is not enable.

Regards

PSM

Richard Burts · ‎07-20-2005

I have just re-read all the messages in this thread and realized something. The show cdp is being done on a distribution switch. Its neighbor should be a core switch. But what is showing up are two other distribution switches (and you said in the original post that there is no direct connectivity between any of the distribution switches). This makes me wonder what is going on with the core switch. I wonder if there is possibly a SPAN port (or monitor port) which is forwarding frames from two distribution connections.

Can you post the config of the core switch to which this distribution switch is connected?

HTH

Rick

HTH

Rick