Wireless router DHCP connected to switch

evanmarshall
evanmarshall used Ask the Experts™
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Situation:

Let's say a person has a wireless router that has 4 ethernet LAN ports on the back of the router.  There are 4 devices connected to the LAN ports on the back of the router and therefore all the ports are used.  There may or may not be devices connected wirelessly.  The wireless router is acting as a DHCP server (assigning IP addresses).

Now that person has a need for more ports to connected wired devices.  A switch (8 port for example) is connected to one of the LAN ports on the back of the wireless router and some or all of the devices that were connected to the back of the wireless router are now connected to the switch.  There are now enough ports for all wired devices.

Here is my question:

How does the wireless router assign IP addresses through the single port that connects the wireless router to the switch, and then to the devices connected to the switch.  I'm under the assumption that each port on the back of the wireless router is only capable of one IP address associated with it (which is assigned by the DHCP function of the router).

Any clarification and knowledge would be appreciate.  Thanks.
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Commented:
The DHCP server running on the wireless router is not assigning the IPs to the individual interfaces.  Instead it is assigning IP addresses to the individual MAC addresses that are querying for an IP.
DHCP just hands addresses out to any device asking no matter how they are attached. A DHCP scope is defined to how many address to hand out not based on the number of ports on a switch. On your Router just have the DHCP setup to hand out as many from 1-254 IP addresses you wish it to hand out. It is only limited by your setting it not by the hardware device.
Agree with both comments above, wanted to maybe explain a bit further. When you do this you are basically creating a bridge from the "Wireless Router" to the "Switch". The Router knows it needs to hand out IP Addresses, nothing is port based it's all based on what's connected down the line. Now when you do something like this you will potentially have traffic issues on that one line depending on the cable type and the switch and router. Best to be running 1Gb/s this way you shouldn't see any performance issues.

Another example is like creating a virtual machine. When you create a virtual machine it actually receives an internet connection with it's own ip address. This is considered a bridge as well. It's quite impressive.
> How does the wireless router assign IP addresses through
the single port that connects the wireless router to the switch,
and then to the devices connected to the switch.

The same way it assigns other DHCP addresses...

1) the client sends a DHCP discovery request to 255.255.255.255
2) the DHCP server responds to the requestor's MAC with an address it has to offer
3) the client replies to 255.255.255.255 requesting the address offered
4) the DHCP server sends an acknowledgement to 255.255.255.255 with the new IP address
Technically, that's the end of the DHCP server's role.

4a) DHCP servers with no scope available respond with NAK.

5) the client queries the network to see if its new IP address already exists
6) if no dupe IP is detected, the client sends an ack to the DHCP server that it's now using the address assigned.

I believe the current DHCP RFC is http://www.ietf.org/rfc/rfc2131.txt

You can watch steps 1 through 4a happen in Wireshark by using the BOOTP display filter.
e.g.
OPPO BDP-83 requesting/getting an IP

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Commented:
Thank you all for your responses.

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