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Not able to reach VLAN between access and core switch

geoivi
Occasional Advisor

Not able to reach VLAN between access and core switch

I have an access point plugged into port 38 on an Access Switch that is not able to reach DHCP on the network.  I set up a VLAN 128 on the access switch and there is a matching VLAN 128 on the core switch with an ip helper-address of 172.16.16.8.   However it seems the AP cannot reach the VLAN at all. I am attaching the switch configs of the access switch and core switch. The access switch is connected at port 1 to core switch on port 44. 

Any assistance as to why i cannot get traffic to flow would be great.  Thank you. 

10 REPLIES
Vince-Whirlwind
Honored Contributor

Re: Not able to reach VLAN between access and core switch

Your 3500 has an IP address in VLAN128 - what is this for?

You need to break this down - connectivity is one thing, DHCP is another.

On the 3500, put one port into VLAN128 as untagged, then give a laptop an IP address in the 172.16.128.0 subnet, attach it to this port and see if you can ping the DHCP server.
If this works, then you need to troubleshoot your DHCP. If not, you need to troubleshoot connectivity at Layer2 and Layer3 first.

geoivi
Occasional Advisor

Re: Not able to reach VLAN between access and core switch

I will test as you mentioned tomorrow.  In the meantime APs are attached to that switch and are functioning.  My gut tells me this is a Layer 2 or layer 3 issue. But i'm having trouble trying to figure out where to look in this case. 

I'll test and get back to you.  Thanks for your help. 

geoivi
Occasional Advisor

Re: Not able to reach VLAN between access and core switch

Any recommendations you can give on the start of troubleshooting the layer 2 or 3 issues would be helpful.  Networking is not my primary field. 

geoivi
Occasional Advisor

Re: Not able to reach VLAN between access and core switch

I plugged a laptop into the network and it worked as you suggested so i don't think it's a DHCP issue. 

It appears i need to take a look at layer 2 or 3.  Any suggestions?

Vince-Whirlwind
Honored Contributor

Re: Not able to reach VLAN between access and core switch

If the test I suggested with the laptop was successful then your Layer2 and Layer3 config is good.

Now you need to troubleshoot your DHCP issue.

So, next, edit your laptop's network config to change it from static to DHCP.
What happens on the laptop?
What happens on the router/Layer3 switch?
What happens on the DHCP server?

geoivi
Occasional Advisor

Re: Not able to reach VLAN between access and core switch

It appears that the laptop gets an IP address.

Which I'm assuming means the DHCP is responding properly. I guess where I'm confused is that everything appears to be fine on the core switch. I've been looking at this from the issue of the access switch.

Other access switches are connected into that core switch without a problem. APs are plugged into those other switches smoothly.
Vince-Whirlwind
Honored Contributor

Re: Not able to reach VLAN between access and core switch

OK, I was suggesting you test your layer2/layer3 connectivity from the access switch, which I think is the 3500:

Give the laptop a static IP address in the 128 subnet and patch it to an untagged VLAN 128 port on the Access switch.
Can you ping your default GW? 
Can you ping IP addresses in a different subnet?

geoivi
Occasional Advisor

Re: Not able to reach VLAN between access and core switch

It looks like the routing is not working.  We set up the laptop with an IP address on that subnet and we got nothing. 

geoivi
Occasional Advisor

Re: Not able to reach VLAN between access and core switch

When i try to ping the IP address i get no reply from the address 172.16.255.2 which is the gateway address for VLAN 902. When i do a tracert from another pc to that address is get a jump from the pcs gateway 172.16.8.1 to the IP 172.16.255.2 and then it dies. so i think it may be routing on the core switch.  It looks to me like the problem must be rooted in that 902 VLAN or the fact that the ip route on the switch is 0.0.0.0 0.0.0.0 172.16.255.1. 

Thank you again for your help. 

Vince-Whirlwind
Honored Contributor

Re: Not able to reach VLAN between access and core switch

You're being a little bit too sparse on detail for me to understand what is going on.

What are you trying to ping, exactly?
Provide the full IP configuration for the device that you are using to do the ping.
Provide the switchport ID of the devices you are using for testing.
Provide updated switch configs if you have changed anything.

The first thing I suggested is - put a laptop onto a switchport on the 3500 that is configured as untagged in VLAN128, and give the laptop an IP address in the 172.16.128.0/22 subnet>
-> ping your default gateway. Success?