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Cannot take ip from dhcp, connection dont go beyond layer-2 switch

svdblbl
Level 1
Level 1

Hey!

I'm trying to make a project in Cisco Packet Tracer and I can't take ip from dhcp. The connection cannot go through beyond Layer-3 switch. I've tried trunking but nothing seems to be working and I ran out of ideas. Please take a look and tell what have I been doing wrong. I've done the routings on the topology. (pls just look at the connected parts)

2 Accepted Solutions

Accepted Solutions

Martin L
VIP
VIP

ip helper-address 172.104.10.2 needs to be placed on L3 switch TOPLAMA int vlan 10 , not on L2; Note that IP here is the IP of DHCP server;

I removed interface vlan 10 config from L2 switch for now;  L2 should not be used (cannot be) default gateway for any PC;  Only L3 switch or router can be default gateway; L2  interface Vlan10 is used for switch management purpose only (telnet to sw and configure it); Since it is static IP, You can add any "reserved"  IP within 192.168.10.x ./24 network to L2 switch interface vlan 10; 

So, remove ip helper command from L2 and add to L3 but use IP of DHCP server; 

Regards, ML
**Please Rate All Helpful Responses ** 

 

View solution in original post

Hello @svdblbl 

 The problem you are facing is related to the fact that DHCP is a broadcast traffic and it will not cross a layer3 device unless you tell it how.

 As you configured interface vlan on the switch I highlighted below, you turned this device into a Layer3 device and you need to add on the interface vlan the command

ip helper-address 172.104.10.2

 

With this command, the switch will take the DHCP request from the PC, will encapsulate it into a unicast packet and send it out to the DHCP server

 

FlavioMiranda_0-1721850613622.png

 

View solution in original post

4 Replies 4

Martin L
VIP
VIP

ip helper-address 172.104.10.2 needs to be placed on L3 switch TOPLAMA int vlan 10 , not on L2; Note that IP here is the IP of DHCP server;

I removed interface vlan 10 config from L2 switch for now;  L2 should not be used (cannot be) default gateway for any PC;  Only L3 switch or router can be default gateway; L2  interface Vlan10 is used for switch management purpose only (telnet to sw and configure it); Since it is static IP, You can add any "reserved"  IP within 192.168.10.x ./24 network to L2 switch interface vlan 10; 

So, remove ip helper command from L2 and add to L3 but use IP of DHCP server; 

Regards, ML
**Please Rate All Helpful Responses ** 

 

Thanks a lot, it worked!

Hello @svdblbl 

 The problem you are facing is related to the fact that DHCP is a broadcast traffic and it will not cross a layer3 device unless you tell it how.

 As you configured interface vlan on the switch I highlighted below, you turned this device into a Layer3 device and you need to add on the interface vlan the command

ip helper-address 172.104.10.2

 

With this command, the switch will take the DHCP request from the PC, will encapsulate it into a unicast packet and send it out to the DHCP server

 

FlavioMiranda_0-1721850613622.png

 

Thank you! It worked!

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