Packet Tracer: Port being blocked by STP

[Matthew L]

Hello all! I am an apprentice in the networking industry who is struggling with a project i've been set.

I have been tasked with implementing a network specification from my tutor in PacketTracer however when the IP phone attempts to obtain an IP via DHCP,  STP blocks the switchport.

Current setup is attached in the image.

-DHCP server/pool has been configured on VLAN 10, my plan is to have VoIP traffic on VLAN 30.

-Inter vlan routing has been setup and I have confirmed it works because PCs in VLAN 20 can obtain IPs, config has been replicated for VLAN 30 (with the appropriate changes)

-I have run the command "spanning-tree mode rapid-pvst" on the multilayer switches

P.S any suggestions for improvement or best practices will be greatly appreciated!

[Flavio Miranda]

Hi

 You can attach the file here to better help you. You need to zip it first.

On the IP phone problem, you may need to setup voice vlan. The phone is send BPDU to switch as it has a "swich inside" 

ex:

Switch#configure terminal

Switch(config)#interface fastethernet 2/5

Switch(config-if)#switchport mode access

Switch(config-if)#Switchport access vlan 10

Switch(config-if)#switchport voice vlan 20

[djzn.br]

I stumbled on this issue tonight. A wireless client was supposed to get a DHCP message reply from a 1941 router offering DHCP in my topology, through a light weight access point via a Wireless Lan Controller, but it failed, STP had it blocked on a L3. Actually, it was a student's issue. I noticed that everything works fine if I configure the switch properly and only then go and cable the LAP on the trunking port from the switch. But when the student cabled the topology first and entered the switch configuration afterwards, the STP would prevent DHCP Discover messages to get past L3 towards the router, same message as OP describes. This wasn't supposed to happen to a real device, was it? Because I fail to see the reason. Could this be a bug in Packet Tracer?   

[Jitendra Kumar]

DHCP server should be in the same subnet since the DHCP discover messages are broadcasts. If your DHCP server is in another subnet then you’ll have to use DHCP Relay:

https://networklessons.com/network-services/cisco-ios-dhcp-relay-agent/

[djzn.br]

Hi. 

I think this could be a genuine problem. The lab in question is the actual SRWE final wireless lab the last time I've seen. However, building it up manually as a PKT, one can notice that there are problems. For instance, no beacon will be found if FlexConnect is not turned on in WLC, but one should get a beacon even with FlexConnect turned off. The router has G0/1 split to1.5 and 1.200 so management network is .200.0 and data network is 5.0, DHCP traffic works alright through the VLAN trunking link (from router to the L3 switch) and the situation I was trying to explain is... if you cable the L3 to the LAP first, before configuring the switch, STP will block DHCP discover messages, even on the same subnet. However, this behaviour is not observed when you configure the interface range f0/22-24 and only then you hook up the LAP afterwards - so DHCP comes and goes freely without STP intervention. What I mean is, the original poster might have been right about this particular misbehaviour of the software. Just so I can put my money where my mouth is, I'm going to try and provide the PKT and some testing. Thanks.