Effects Of Two Dhcp Servers

[nikster]

Hi,

I often find myself in a situation where there are 2 DHCP servers on a network, and there is nothing I can do about it. This happens a lot with wireless - even so-called "experts" set up WiFi in this way. E.g. there is a Router/DSL modem running a DHCP server AND connected to that there is a wireless router which also has a DHCP server running.

Now I know that's stupid - however, it works by and large. But I often have networking issues on these networks, either getting a DHCP address - when both DHCP servers are on the same number scheme - or now with VPN.

Arguing this with the people in charge is useless, you might as well speak Russian to them. When you say "DHCP" their eyes sort of glaze over and all they hear from that point on is "blah blah blah". Understandably, no one should have to care about such things, these machines should just work, but that's a different story.

So two things:

1) If both DHCP servers are on the same numbering scheme, what are the effects?

2) If both DHCP servers are on different numbering schemes, would this explain that VPN can't connect _sometimes_? I am on such a system right now, and VPN seems to work for long periods of time, then suddenly disconnect and simply not connect anymore for a while, then slowly reconnect.

I can rule out that the VPN issues are caused either by my client or by the server in the U.S. because as soon as I connect through my GPRS cell phone, it works every time and is completely stable.

I can also rule out a general downtime for the network because internet pages still load fine when the VPN goes down.

[lingling]

Hi,

I often find myself in a situation where there are 2 DHCP servers on a network, and there is nothing I can do about it. This happens a lot with wireless - even so-called "experts" set up WiFi in this way. E.g. there is a Router/DSL modem running a DHCP server AND connected to that there is a wireless router which also has a DHCP server running.

Now I know that's stupid - however, it works by and large. But I often have networking issues on these networks, either getting a DHCP address - when both DHCP servers are on the same number scheme - or now with VPN.

Arguing this with the people in charge is useless, you might as well speak Russian to them. When you say "DHCP" their eyes sort of glaze over and all they hear from that point on is "blah blah blah". Understandably, no one should have to care about such things, these machines should just work, but that's a different story.

So two things:

1) If both DHCP servers are on the same numbering scheme, what are the effects?

2) If both DHCP servers are on different numbering schemes, would this explain that VPN can't connect _sometimes_? I am on such a system right now, and VPN seems to work for long periods of time, then suddenly disconnect and simply not connect anymore for a while, then slowly reconnect.

I can rule out that the VPN issues are caused either by my client or by the server in the U.S. because as soon as I connect through my GPRS cell phone, it works every time and is completely stable.

I can also rule out a general downtime for the network because internet pages still load fine when the VPN goes down.

Absolute and utter chaos, unless the dsl modem is plugged into the wireless router's "external / internet" port. In that case, the dsl modem's dhcp should only assign an address to the wireless router's external interface. (dhcp traffic will not be routed)

If, for some reason, the dsl modem is plugged in on the "internal" side of the wireless router you need to switch off the dhcp in the wireless router. (however, if this is a wireless router and not a wireless access point I can't see any reason why the dsl modem would be connected to the "internal" side of it - use the router as a router and not an access point).

[A_Traveller]

Forgive the post and run, but I'm on my way out of the door. The short answer is that one should never have two DHCP servers on a single network unless the two are running as a coordinated cluster. i.e. two machines providing fail over for each, meaning that the leases {addresses} issued by them both are coordinated.

Regards