Port forwarding------- modem or router or both

[apostolakisl]

So, if instead of plugging it into your router, what if you plugged it into a switch with 2 or more things attached?  The first thing that asks would get the public IP address, but what would it give the other things?

 

[pete_c]

Typically you would:
 
1 - connect the ISP WAN link to your GT701
2 - connect the ethernet port to the WAN ports of your Cisco E3200
3 - connect your Elk to one of the LAN ports on the Cisco E3200
 
Configure your Cisco E3200 such that it port forwards port in question from WAN port on the Cisco E3200 to LAN IP of the ELK whatever LAN port its on.  Some routers also let you configure the specfic LAN port for whatever you want say if you connect the ELK directly to said physical LAN port.
 
Simple as that.
 
Your modem (DSL) is really another router with a configuration that you cannot get to or modify typically.  Your ISP can though modify the configuration file for said modem.  Depending on the configuration from the ISP the modem can dole out DHCP NAT'd addresses or bridge one (or more) addresses to LAN port.  Typically too the MAC address of the inside router is utilized for the modem or a default one already configured inside of the modem.  Typically if you see a public IP on the WAN port of your firewall then its just the bridged IP your are seeing coming from the modem.  The rule's / configuration set in the modem is still in place and doing its job.  The configuration file on the modem also contains the designated service tier that your ISP is providing to you along with other stuff and is typically based on the MAC address of the modem itself. 
 
IE: your modem boots up; does a TFTP to the ISP provider, checks the MAC address to a DB which includes your service et al, then drops down the configuration file to your modem.  It does the same with the firmware on your modem if it needs to be updated.

 

[tmbrown97]

So, if instead of plugging it into your router, what if you plugged it into a switch with 2 or more things attached?  The first thing that asks would get the public IP address, but what would it give the other things?

typically the first device to register gets the only available IP and the rest of the devices end up with nothing.  Seen it a bunch of times in this neck of the woods.  This is also a security hole because most of the time the device that registers doesn't have proper firewall protection.  I've even seen it with a wireless bridge where the first wifi client gets the one and only available IP.

 

[apostolakisl]

typically the first device to register gets the only available IP and the rest of the devices end up with nothing.  Seen it a bunch of times in this neck of the woods.  This is also a security hole because most of the time the device that registers doesn't have proper firewall protection.  I've even seen it with a wireless bridge where the first wifi client gets the one and only available IP.

 
OK, makes sense.