PACKET TRACER: DHCP and VLAN configuration

[SteveScorse]

Hello, I am in the process of trying to configure DHCP for my VLANS and am having some trouble. So far I have:

• Configured my DHCP pool
• Added the VLAN(s) to the L3 and L2 switch
• Configured the VLANS on the switches
• Enabled Trunking on the necessary ports

I'm not sure why I am unable to get DHCP working, any help would be greatly appreciated.

NOTE : (I am currently configuring VLAN 101, on Floor2 - F2 Multilayer Switch and F2GSwitch0 - just to try and get a VLAN working before I implement it across all switches)

Attached is my PT file - I fear I may be unclear or missing something entirely and am more than welcome to clarify on any info I've missed out on. Many Thanks.

[marce1000]

 - You may also ask that in https://learningnetwork.cisco.com/s/topic/0TO6e000000WEorGAG/packet-tracer 

 M.

[SteveScorse]

I wasn't aware of this, thank you very much!

[M02@rt37]

Hello @SteveScorse

some details are wrong concerning your configuration.

On Sw 2960 delete SVI (interface vlan X)

On Multilayer Switch add ip helper-address command like this:

AS concerned this Multilayer Switch, modify the port facing the DHCP server, mode Trunk is not good ! Modify with switchport mode access vlan 201:

Also, take care, all Gateways on your DHCP server are wrong! Configure like this:

After that, this PC has got this IP with DHCP.

[SteveScorse]

Hi, thank you very much for your response! I have a couple of questions regarding the answers you gave as I am quite confused, apologies as I am new to networking.

"On Sw 2960 delete SVI (interface vlan X)" - what does this mean - do I need to remove the VLANs from that switches database?

"AS concerned this Multilayer Switch, modify the port facing the DHCP server, mode Trunk is not good ! Modify with switchport mode access vlan 201:" - why would I set the VLAN for the port facing the DHCP server to access and not trunk where it has all VLANS available to it? And why VLAN201?

"Also, take care, all Gateways on your DHCP server are wrong!" - Why are the gateways their own network and not the main routers?

Sorry for not understanding, I really appreciate your response!

[M02@rt37]

You're welcome @SteveScorse 

"On Sw 2960 delete SVI (interface vlan X)" - what does this mean - do I need to remove the VLANs from that switches database?

-- Delete the interface VLAN not the VLAN. Let your 2960 as a traditional L2 Swich. 

"As concerned this Multilayer Switch, modify the port facing the DHCP server, mode Trunk is not good ! Modify with switchport mode access vlan 201:" - why would I set the VLAN for the port facing the DHCP server to access and not trunk where it has all VLANS available to it? And why VLAN201?"

-- The DHCP server is a host! A host with an IP address. Its Gateway is the interface's Router facing to it. Then it is not a Trunk port, it is a access port. The router is in charge to route packet from/towards this DHCP host interface towards/from different subnet.

"Also, take care, all Gateways on your DHCP server are wrong!" - Why are the gateways their own network and not the main routers?

-- Gateways are IP on the same subnet than their respective host. Your host need to know where to send packet towards an other subnet...this is the Gateway role to do that. That Gateway has to be in the same subnet !

[Martin L]

in addition to what M02 mentioned L3 should be doing Routing for vlans near by in access layer but it has ip routing turned off; Note this model in PT comes with no ip routing by default.  While L2 switch should just have 1 IP on SVI for management purpose, L3 device (either router or L3 sw) should performed role of default gateway for PCs in access layer. In order to do that, all SVIs on L3 sw should be up/up state. Switch SVI Interfaces will stay down if vlans are missing from vlan database and there is no trunking or no hosts connected to particular access vlan.

Useful commands to TS issues on switches:  show ip interface brief, show interfaces trunk, sh vlan brief, show ip route (L3)

Regards, ML
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