Letting a second router through the SMCD3GN

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I Plan to Stick Around
Posts: 9

Letting a second router through the SMCD3GN

I currently have an SMCD3GN router through Rogers.  I am connecting a Cisco 891 to it, using the SMC as the external WAN.

 

For examples sake, let's say the internal IP on my SMC is 192.168.150.1.  The 891 has an IP connected to the 192.168.150.0 network of 192.168.150.150.  The other side of the 891 is 10.10.10.1 (the default for the 891.)  Anything connected to the 891 (say a device with an IP of 10.10.10.100) can ping both sides of the 891, and also the internal IP of the SMC.  That's it.  It can't ping any machines I have on the 192.168.150.0 network, and can't ping anything on the outside (past the SMC.)  From a machine on the 192.168.150.0 network I can ping everything, including the 10.10.10.100 machine (due to me putting a static route on the SMC pointing to that network.)  If I add a static route to my 192.168.150.101 machine, the 10.10.10.100 machine can now ping that machine also, but nothing else.

 

Is there a way to set up the SMCD3GN to allow me access from the 891 and it's corrosponding network to the outside, and the rest of my 192.168.150.0 network?

I called Rogers and asked if I could get a secondary IP (which would make my life a lot easier with this!) and I was told that wasn't offered anymore.  😛  I would put the SMCD3GN in gateway mode and add another router between the 891 and the SMC, but that's just not feasable at the moment with the way things are set up here (have to deal with family in the house that also uses the internet!)

If anybody has any ideas, please let me know!  Thanks!

 

 

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I'm an Advisor
Posts: 928

Re: Letting a second router through the SMCD3GN

Can you take a step back and explain exactly what you are trying to do?
 Are you trying to keep family members away from the 891's network?

 

I guess I'm just confused about why you can't just put the SMC in bridge mode (well, really, you should replace that SMC with an 8 or 24-channel modem) and put everything behind the 891. If you can elaborate on why that won't accomplish what you want, perhaps we can come up with some good ideas...

Resident Expert
Resident Expert
Posts: 13,948

Re: Letting a second router through the SMCD3GN

Yeah, i would agree.. explain to us, what you are trying to do...

Alot of it seems possibly un necessary.. and maybe we can come up with a better solution.



I'm an Advisor
Posts: 928

Re: Letting a second router through the SMCD3GN

This may be a totally absurd idea (remember, I'm not sure I understand the problem), but if you need two subnets, why not bridge the Rogers modem, then get a fancier router (I don't know how fancy you'd need to get) with two interior interfaces.

 

Then set up the fancy router like this:

- WAN port - Rogers

- LAN port #1 - 192.168.150.1 - connected to one network

- LAN port #2 - 10.10.10.1 - connected to other network

... and the fancy router NATs traffic from both subnets to the outside, while allowing traffic to be routed between the two subnets without NAT.

 

This would be easy enough to do with an x86 box running Linux, FreeBSD, etc. and three NICs. If you're trying to use something more specialized, I don't know who makes software that would let you do this. Maybe the Tomatos and DD-WRTs of the world do...

Resident Expert
Resident Expert
Posts: 6,147

Re: Letting a second router through the SMCD3GN

If its a matter of having enough ports for all of the devices, you would be better off placing the 891 behind the SMC and then placing an unmanaged 8 port gigbit switch behind the 891.  As Gdkitty and VivienM have said, let us know what you need to accomplish.



I Plan to Stick Around
Posts: 9

Re: Letting a second router through the SMCD3GN

I'm trying to do this (let me see if I can diagram as best I can with no real art tools!)

 

XXXXXXX - SMCD3GN

I       I

I       I

I       --- Rest of network attached to here

I

I

I

XXXXXXXX - 891

I

I

I

I------- Test network

 

I don't want to put the SMC into bridged mode, because I don't plan on being here that long (wife and I are looking for a house and moving out of her mother's place) and I don't feel like reconfiguring all the other bits and pieces around this house.


I'm using the 891 as a "learning device" (I work for an ISP, oh how I wish they could give me free internet at home, but I live too far away from them for anything better than 6/1 DSL) to figure out how to get it to work the same as, or as close to, an ASA5505 as I can.  So, I'm building a small network behind it, and have it plugged into the SMC, using the SMC as the "ISP" so to speak.

 

So, I want to configure the SMC to let the 891 traffic through it.  That's it.  I don't know if that can be done (as a side note, I do have full access to the SMC, so that's not an issue.)

 

Granted, my company may be putting a line in here for me (again, 6/1 DSL so it won't be my main internet, just something I can play around on, and thank the goddess they let SMTP traffic through so I can have my own mail server, as opposed to Rogers not allowing it) so it all my be for naught, but I still want to know if it can be done.  Without putting anything in gateway mode (which I would do if I were staying here, or if I didn't have to worry about other people in the house on the internet.  They like things the way they are, and considering that they're the ones paying for it, I really can't just do what I want.)

 

If it were my own place, I'd have this thing wired the way I wanted anyway, and wouldn't be having this issue.  I just need to know if it can be done through the SMC or not.

I'm an Advisor
Posts: 928

Re: Letting a second router through the SMCD3GN


@Corbeau wrote:

I'm trying to do this (let me see if I can diagram as best I can with no real art tools!)

 

XXXXXXX - SMCD3GN

I       I

I       I

I       --- Rest of network attached to here

I

I

I

XXXXXXXX - 891

I

I

I

I------- Test network

 

I don't want to put the SMC into bridged mode, because I don't plan on being here that long (wife and I are looking for a house and moving out of her mother's place) and I don't feel like reconfiguring all the other bits and pieces around this house.


I'm using the 891 as a "learning device" (I work for an ISP, oh how I wish they could give me free internet at home, but I live too far away from them for anything better than 6/1 DSL) to figure out how to get it to work the same as, or as close to, an ASA5505 as I can.  So, I'm building a small network behind it, and have it plugged into the SMC, using the SMC as the "ISP" so to speak.

 

So, I want to configure the SMC to let the 891 traffic through it.  That's it.  I don't know if that can be done (as a side note, I do have full access to the SMC, so that's not an issue.)

 

Granted, my company may be putting a line in here for me (again, 6/1 DSL so it won't be my main internet, just something I can play around on, and thank the goddess they let SMTP traffic through so I can have my own mail server, as opposed to Rogers not allowing it) so it all my be for naught, but I still want to know if it can be done.  Without putting anything in gateway mode (which I would do if I were staying here, or if I didn't have to worry about other people in the house on the internet.  They like things the way they are, and considering that they're the ones paying for it, I really can't just do what I want.)

 

If it were my own place, I'd have this thing wired the way I wanted anyway, and wouldn't be having this issue.  I just need to know if it can be done through the SMC or not.



Okay, I think your problem isn't with the SMC.

 

Your problem is with routing tables... and it won't be "pretty" to fix.

 

Assuming the 891 isn't doing any NAT, the problem is that the 'rest of network', hooked up to the SMC, don't have a route to the SMC's internal subnet. So they send those packets to the default gateway (the SMC)... which has no idea where to route them to either.

 

I don't have the ability to see your actual IPs (the reply interface doesn't show your original post), but let's say the 891's 'outside' IP is 1.2.3.4., and the 891's internal subnet is 2.3.4.0/24, then you'd need to go to every machine plugged into the SMC other than the 891, and do something in the command line like

route add 2.3.4.0 netmask 255.255.255.0 1.2.3.4

(that syntax should work in Windows NT-based OSes)

 

(The machines behind the 891 should be fine, since their default gateway is the 891, and the 891 is on the same physical subnet as the other machines and therefore knows how to route to them. It's the route back that's the problem.)

 

Time for you to look up the command-line commands to add routes in your favourite OS, I guess.

I Plan to Stick Around
Posts: 9

Re: Letting a second router through the SMCD3GN

From my SMC network I can ping anything on the network, including everything on the 891 network (192.168.150.0 and 10.10.10.0 respectively.  That is with using the static route on the SMC to tell everything on its network where to send things for 10.10.10.0.  And it works.  From the 10.10.10.0 network, I can ping 10.10.10.1 (the 891 on the one side), 192.168.150.150 (the 891 on the SMC side) and 192.168.150.1 (the SMC).  I cannot ping anything else.  If I add the route to my machine on the SMC network, I can then also ping that machine from the 10.10.10.0 network machine.  But I still can't get to the internet.  That is stopped at the SMC, I'm guessing.

 

I need the 891 network to be able to get out to the internet.  It knows where the gateway of last resort is (it's a static on the 891, pointing to the SMC) but it just stops at the SMC (remember, I can ping the SMC with no problem from the 891 network machines.)

Resident Expert
Resident Expert
Posts: 6,147

Re: Letting a second router through the SMCD3GN

My question would be whether or not the ability to ping inside the SMC network and communicate device to device is important.  My home network is very similiar to your diagram, the only difference is an unmanaged gigabit switch in between the two routers.   Substitute new CGN3 for SMC and older Dlink DIR-655 for your 891.  With nothing else hooked into the switch, my network would look like yours.  It can be done very easily.  Disable the DHCP on the 891 and set it to accept the address that the SMC assigns to it and leave the firewall functioning.  As long as you are not fussy with the device addresses, they will originate from the SMC.  I've run this same configuration with the SMC, the DCP3825 and now with the Hitron CGN3.  In my case the second router functions as an access point, and is invisible to the network but it will run wired or wireless as required and ping the outside world as required.  If I ever have to reset any item, I have to reset back to factory defaults, make the changes, save and reboot.  Back in business.  I haven't looked at the settings for weeks, and normally have no need to.  You could probably set the second router to an address completely outside of the range of the SMC, and enable the DHCP for the 891 in order to assign its own address to devices that are connected to it.  In that case you should be able to log into both routers when needed. As long as you are normally running pc's / laptops etc. behind the 891, the first configuration with the DHCP disabled should work for you.



I'm an Advisor
Posts: 928

Re: Letting a second router through the SMCD3GN

Okay, I think I see the problem.

 

The SMC, like most such devices I would guess, is only going to do NAT for traffic with a source IP that matches its 'interior' IP range (i.e. 10.10.10.* if I read your example right). If the 891 traffic hits the SMC with a source IP of 192.168.150.2, then whooops, it's not going to be NATted. (And no NAT means it's not going out)

 

I very much doubt the SMC, or any other 'consumer-grade' NAT device for that matter, can be configured to do something as fancy as what you'd need.

 

One 'solution', as ugly as it would be (and it would break other stuff): can the 891 do its own NAT? then the traffic would hit the SMC with the 891's 10.10.10.whatever IP, and the SMC would happily NAT it again and send it out)