891F Dual WAN configuration with same subnet (overlap error)

[nbaker011]

I suspect I'm running into a non supported configuration. The situation is that I have a range of public IP addresses provided by my ISP, e.g.:

10.10.10.254 << modem / gateway address

10.10.10.249-254 << public static IP for me to use

255.255.255.248 << mask

I have assigned 10.10.10.249 on the Gi8 interface using dhcp on the modem

I have assigned 10.10.10.250 on the Fa0 interface using dhcp on the modem

Only Gi8 gets a stable ip address, Fa0 keeps releasing and requesting (until I shutdown Gi8 say).

If I manually configure Gi8/Fa0 using say:

int Gi8 ip address 10.10.10.249 255.255.255.248

int Fa0 ip address 10.10.10.250 255.255.255.248

I get the following error:

% 10.10.10.248 overlaps with GigabitEthernet8

So, from what I can tell from other posts I can not assign addresses this way, even thought this is what the ISP provides me. Is the solution in my case 2 routers, or is there a way to get this to work with narrowing the mask on both interfaces, even though the ISP defines my address range as above?

Thanks,

Nick.

[Jason Vanlandingham]

No device likes to have more than one interface in the same subnet. Narrowing the mask would result in only one of the interfaces being able to reach its gateway. I can't imagine a configuration where you'd want to do what you're describing though. Can you describe the setup and goals?

If this is a lab type environment, and you're just doing this to play with configurations, I'd suggest you do the two router setup - pick up a used 1811 or 2801 or something like that on Amazon/eBay. They're cheap, and it will give you plenty of options to play with routing protocols, etc. Heck, even a 3825 or 3845 can be found for not too much, and they still have enough horsepower to be perfectly usable on a modern network.

[nbaker011]

Thanks - yes the theory was that I could have two VLANs on the LAN side one connected to say the 10.10.10.249 public network and the second for the 10.10.10.250 public network address. I'm doing this with two routers today, but after upgrading to the 891F on one of the networks I was testing to see if I could use the dual WAN feature to accomplish the same thing - seems like I can't, so thanks for confirming.

[fbeye]

It appears we are wanting the same outcome.

Currently I have a vDSL Router in Bridgemode connected to a TPI-Link Router which 1.) controls pppoe authentication and 2.) has a Static ip assigned to it as the gateway and then offers my 5 other Static ips to the various devices I have.

my goal/ ambition is one of 2 if possible.

to keep vDSL In Bridge and use my 891f-k9 as 1.) pppoe authenticator and as the gateway and assign the 5 ips to their designation as its own subnet (the statics from the gateway Static) with port /firewall control 

or

the keep my system as is; vDSL to TP-Link then add 2 WAN IP’s on 891f and then do a LAN Subnet (182.168.0.1 style) with Port forwarding .

are either my Of scenarios possible?