Solved: Packet trace 2960 switch dropping packets

imood · ‎03-19-2023

Why does a 2960 switch drop packets from a layer 3 switch, with the message "switch does not have the Vlan indicated on the IEEE 802.1q frame tag. It drops the frame" in packet tracer, all vlans and inter vlan routing was configured?

David Ruess · ‎03-19-2023

OK I was able to take a look. After seeing the full configs and setup I don't think that will work. Apologies I gave you some wrong information based on some assumptions. I have attached the PT file configured a bit differently.

The reason it wasn't processing the packet is because the switch is using a trunk port (to allow all VLANs to get an IP from it) but the server doesn't know how to process VLAN tags so it drops it. It needs its own subnet. Also you configured the .193 address as the helper which is the DG of the DHCP server. You need the IP of the DHCP server itself.

Changes I made:

Configured the DHCP server port on SW3 as an access port assigned to VLAN 40.

Configured the helper address of 192.168.1.195

PC0 was able to get an IP address after that. I ahve attached the PT file.

I aslo fixed a couple other things. The connection between R0 and the MLS was not in the same subnet. You were using a /30 but the interfaces IPs were in different /30 networks. I made them the same. Also your OSPF config on the MLS was configured wrong (if you were trying to advertise those VLAN subnets). You were activating OSPF on interfaces that didnt exist.

For example you had:

network 192.168.2.0 0.0.0.63 area 0

when the interface was the 192.168.1. subnet. I added the .1 interfaces but left the .2 interfaces if you want to check it out

Hope that helps

-David

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David Ruess · ‎03-19-2023

Hello,

Can you provide the vlan database, trunk configurations, and screenshots of the error or what it shows that its dropping packets?

-David

imood · ‎03-19-2023

The problem arises when pcA on switch 0 request for an ip from the dhcp server on switch 4 when the layer 3 switch for wards the packet to switch 4 it drops it.

MHM Cisco World · ‎03-19-2023

share the config of SW and R

imood · ‎03-19-2023

I shared it below, it's the layer 3 switch

imood · ‎03-19-2023

The problem arises when pcA on switch 0 request for an ip from the dhcp server on switch 4 when the layer 3 switch for wards the packet to switch 4 it drops it.

David Ruess · ‎03-19-2023

Did you also create the VLAN 40 on the L3 switch. If you just created the SVI it does NOT automatically create the L2 instance which is needed to complete the path.

You didn't provide any VLAN database for wither switch and you don't have a PCA. You have a PC0 and a PC1 so not sure which one it is.

On the L3 switch make sure the command is entered:

conf t

vlan 40

YOu will also need to do this for all other VLANs that need communication from the other switches

Show the vlan database on the L2 and the L3 switch if that didn't solve your issue:

show vlan

Please also show the trunk interface (to make sure its allowed on the interface).

-David

imood · ‎03-19-2023

PC0 not A, I configured vlan 40 already.

David Ruess · ‎03-19-2023

I think you switched some things. From your first couple of pictures you show that SW3 drops the traffic due to no VLAN but you say its from PC0. PC0 is connected to switch 0 with VLAN 10. PC0 shouldn't even be reaching switch 3.

Can you check all your access switches to ensure the correct VLAN is on them and configured on the access ports attached to the PCs.

From your picture Switch0 should be all VLAN 10 with PC0, and Switch3 should be all VLAN 40 with PC1 connected. Please verify this is correct.

-David

imood · ‎03-19-2023

Yes, Switch0 is VLAN 10 with PC0, and Switch3 is VLAN 40 with PC1 connected. Switch 3 is the one who drops the packets.

imood · ‎03-19-2023

The Dhcp server is also on switch three, the layer 3 uses the helper address and forwards the packet to switch 3 which drops it

David Ruess · ‎03-19-2023

Can you create VLAN 10 on Switch 3. And also make the port connected to the DHCP server a trunk port and make sure VLAN 10 (and all other VLANS) are allowed.

If the DHCP server is on SW 3 then it will just get to the L3 switch and be sent on the trunk port to Switch 3. I dont think it hits the SVI because it doesn't need to.

-David

imood · ‎03-19-2023

It forwarded it to the DHCP server, but the server now drops the frame

David Ruess · ‎03-19-2023

Are DHCP services turned on on the server. Have you assigned a pool for VLAN 10? Can you show the screenshots of the server and what networks you have configured on there for DHCP. It should be 192.168.1.0 255.255.255.192.

imood · ‎03-19-2023