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I have the following network:

network diagram PCVLAN10 -> SWITCH_LAN1 -> ROUTER_LAN 1 -> ROUTER_LAN2 -> SWITCH_LAN2 -> DHCP(ROUTER)

I have set up subinterfaces on the routers, and allowed trunking on VLAN 10 on all devies.

What I want to achieve: PCVLAN10 should be able to receive an IP from the DHCP on LAN2.

What happens is: The traffic runs smoothly to DHCPRouter from PCVLAN10 and according to the simulation mode in Packet Tracer an address from the pool has been choosen and is prepared to be sent out, but never is.

If I put a computer on the same vlan but connect it to switch 2, that computer is able to receive an IP. So it has to be something with the switch and router 2 on the way back.

I have set up IP Helper adresses along the way and default routes, but somewhere the traffic just stops without giving me proper information.

What do you guys think might be the error?

EDIT: I've added a helper adress on the way back. The result is a bit irritating though, it takes quite a while for the PC to get the DHCP-address, my pools excludes adresses 1 - 3 but the next one recieved is "44" and if i release that and request a new one I get 49, does this mean that the dhcp server is unable to route the 5 packets?

Daniel
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Whatcouldbewrong82
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  • Downvote? Why is this a bad question? – Whatcouldbewrong82 Apr 14 '16 at 06:49
  • Please upload the picture through Serverfault. The ad-funded image hister might be the reason for downvote. – Daniel Apr 14 '16 at 07:58
  • Mouse over the down arrow; the popup says "*This question does not show any research effort; it is unclear or not useful*". Downvotes without comment may be presumed to be for at least one of those reasons. – MadHatter Apr 14 '16 at 08:18

1 Answers1

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Two networks mean two broadcast domains. Since DHCP communicates over broadcasts, the packet is dropped at the network boundary, say: the router. You need to configure the router to relay DHCP communication between the networks.

Now you have a second problem: Your DHCP server will need to know that the computer is in another network and so needs an IP address in a different network range.

I suggest you read about broadcast domains, broadcasts and how DHCP works to get a better idea of the issue.

Another question, though off-topic, is, why you don't give the computer a static address. Your conception is quite uncommon.

Daniel
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    I think part of the problem this answer may not touch on is a misunderstanding about what a VLAN is. a VLAN is a segmentation of an otherwise single broadcast domain. I think the poster confused the fact that I CAN apply the same VLAN to more then one subinterface to segment more then one actual broadcast domain. To clarify, i think the origional poster might need to better understand - Routers are not switches and will never forward broadcasts, even if VLANS match. – Nick Young Apr 14 '16 at 11:37