Able to see switch through CDP, but can't ping/telnet

kemgs20 · ‎06-29-2007

We are having connectivity issues with a couple of our 3750 switches. The devices were working a week ago but now we can't connect remotely or ping. Switches are showing up in CDP neighbors. Any ideas of what could have happened, or how to fix them remotely?

glen.grant · ‎06-29-2007

If you cant get to them then you have to go in thru the console to look at the parameters . Check for things like no exec-timeouts on the vty's that would tie up all the vty lines.

guruprasadr · ‎06-29-2007

HI, [Pls Rate if HELPS]

Was there any Changes in the Configuration recently. Other than CDP neighbors Updates, Do you see in the "show ip route" table still the neighbors / routing Updates exists.

I hope in the CDP table you are seeing the previous History only. Can you please check again by clearing the CDP Table. Use "Clear cdp table" in the privileged EXEC mode.

Then Execute the "show cdp neighbors" command. (or) even turn OFF the CDP globally using "no cdp run" & then turn ON after few minutes in the Switch.

At last, if nothing work fine then you will have to try connecting via Console Access to Check what is happening....

If possible can you pls post the Configuration.

Hope this Helps you

PLS RATE if HELPS

Best Regards,

Guru Prasad R

srimural · ‎06-29-2007

Hi,

CDP works at Layer 2, I doubt the L3 is not UP or something blocking it. If your can share the configs that will be great.

Thanks and Regards,

Sri

guruprasadr · ‎07-01-2007

HI,

I accept the suspection of Sri.

CDP works at L2 but if the IP Layer is not UP means you can't take the control of the Device.

Can you post your Configuration to investigate more on this.

Best Regards,

Guru Prasad R

FMaster007 · ‎08-31-2020

Hello! I am running into this problem as well but a bit different setup. I have two Unifi AirFiber setup as Point-2-Point to connect both buildings together. I have a Cisco 2960x on the new building set up as a Layer 2 and using the command IP default-gateway (the gateway of the switch working as an L3. I can ping both Unifi AirFiber, I can see the Unifi controller and Unifi WAPs, but I cannot ping or SSH to the switch using the IP address on the VLAN (VLAN-ID 93 in this case).

Also, both ports are trunk where the Unifi AirFiber connects to pass-thru 4 VLANs.

Do I need to put the switch on the new building as an L3 and put the static IP address?

Thanks!

Georg Pauwen · ‎09-01-2020

Hello,

post a schematic drawing of your topology. From where can you not Telnet/SSH to the switch ? What are the IP addresses configured on the two devices ?

FMaster007 · ‎09-01-2020

Hi Georg,

Here's a high-level sketch of the topology.

I have a switch in the old building that's the gateway for the subnet 10.1.20.0/24, and that switch has an IP address of 10.1.20.254 using as its default gateway to its next hop which is the core switch. The switch 10.1.20.161 is where the Unifi Airfiber connects, is this switch is IP routing enable and default-gateway (this is not a Cisco switch, it's an Aruba 2920 switch). There is another switch that connects to 10.1.20.161, which is 10.1.20.134 and it only has default-gateway enable which is 10.1.20.254. On the new building, where the Cisco 2960x is located, I've enabled only IP-default gateway (using IP 10.1.20.254) and put an IP address on VLAN 93 10.1.20.172 (which is the same network/subnet). Both ports on the Aruba 2920 (int eth 12) and Cisco 2960x (int gi1/0/24) where the Unifi Airfiber connects are configured as trunk (cisco) and tagged (Aruba) to allow multiple VLANs.

Hope this makes sense. Thanks again!

paul driver · ‎09-01-2020

Hello

@FMaster007 can you ping the switch from the l3 core sourced from its own vlan interface, if so that will mean that switch's addressing is in someway incorrect ( wrong default gateway address or subnet mask) or you have ip routing enabled on that switch?

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Kind Regards
Paul