Can the firewall prevent the DHCP to give an address, how to fix this?

Question

I am not getting an IP in the subnet 10.0.0.0/24 where the DHCP is working and should serve an IP, I am getting instead only an IP in the subnet 169.254.0.0/16(link local address) that is probably given by Windows which runs on the laptop I am using to test this, which makes me think it might be a problem of the network firewall blocking the DHCP Discovery service.

And if that is caused by the firewall, which ports I should be opening for DHCP Discovery to work?

Did you try to plug the cable in anoter computer? Just to check the connection to the switch is working, the port is correctly configured ... — alphamikevictor, May 11 '15 at 15:34
@alphamikevictor yes I did, the same, also the inteface LEDs light up normally. — Eduard Florinescu, May 11 '15 at 15:35
When you say the same, do you mean the other computer is also receiving `169.254.0.0/16` address? If it is the case then looks like the configuration of this port switch is not the right one. — alphamikevictor, May 11 '15 at 15:37
@alphamikevictor »"the configuration of this port switch is not the right one" Can you please be more specific ? — Eduard Florinescu, May 11 '15 at 15:40
For example, it could happen this port is configured in a VLAN with no DHCP or no DHCP-relay — alphamikevictor, May 11 '15 at 15:42
Also keep in mind that DHCP is a broadcase-based service, it can't cross vlan boundary. If client and server are not on same segment, you need DCHP proxy — strongline, May 11 '15 at 15:45
Is the DHCP server on the same physical network segment or VLAN as the client? If so, then the problem is not the network firewall. — joeqwerty, May 11 '15 at 15:59
@alphamikevictor actually it was port configuration problem can you write your comment as an answer so I can vote, accept — Eduard Florinescu, May 12 '15 at 14:10
@EduardFlorinescu glad it helped you to solve the problem :) — alphamikevictor, May 12 '15 at 14:22

score 1 · Answer 1 · answered May 11 '15 at 15:42

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DHCP Server UDP 67

DHCP Client UDP 68.

There are other ports requirements for different things depending on the implementation, but above is standard.

answered May 11 '15 at 15:42

strongline

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score 1 · Answer 2 · answered May 11 '15 at 15:46

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I am going to assume you have a firewall (of some sort) between your machine, and the DHCP server - is this the case?

If so, does this firewall also route traffic? You may be required to switch on a DHCP helper (This is due to the fact DHCP uses broadcast traffic which routers will not forward on to other segments)

If this is not the case, have you tried some basic troubleshooting - i.e. plug in a device with no firewall. Does it get a DHCP lease? (i.e. is the problem common to all devices, or is it just certain devices)

Please give us some more information.

answered May 11 '15 at 15:46

Snellgrove

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I don't have that information I don't "own" the network, I can request just outbound/inbound rules and exceptions – Eduard Florinescu May 11 '15 at 15:54
Not an insurmountable problem! How many nodes do you have on that network that can grab a DHCP lease? I'm hoping you have more than one. It may help you figure out whether it's a certain node with an issue (suggesting a localised configuration problem) or all nodes with the same behaviour (suggesting a network firewall or router not forwarding to the DHCP server). – Snellgrove May 12 '15 at 13:49

score 1 · Accepted Answer · answered May 12 '15 at 14:21

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As stated in the comments:

Check with another computer to see if the problem appears in other computers
If it is the case check the configuration of the port this computer was plugged, as probably is configured in another VLAN.

answered May 12 '15 at 14:21

alphamikevictor

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Can the firewall prevent the DHCP to give an address, how to fix this?

3 Answers3