Two Cable Modems w/ Same IP
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I'm trying to multi-WAN two Cable ISP's. Both have the same management IP (192.168.100.1). How can I have both coexist such that I can access the management GUI for both?
ONE way is simply to create a static route and swap back and forth between which gateway it routes to.
But that's mighty inelegant. Is there some way I can do a NAT rule or something that would, say, allow 192.168.100.2 to go to Gateway 2 but then translate to 192.168.1001. on that gateway?
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Can you not simply change the ip/dhcp settings on one of the modems? I personally have never seen one that you can’t change those settings on.
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@gabacho4 No, sadly, both Arris and Motorola GUI's don't offer any way to change the admin GUI IP. I bought one of each thinking they'd have different IPs but they both have them statically assigned to the same dadgum one.
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@ptyork In situations where I've seen this before the suggestion has been to turn on PBR and only allow one gateway to be managed at a time and turn them into bridging mode so you get public IP addresses on the devices.
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@ptyork that’s a major bummer. I personally would have to do some research but I wonder if there is a way to mark packets based on their port of origin or destination and then route them based on mark. I know of at least one other router/firewall company that has that kind of feature set but I’ve never looked into it on pfSense. Your proposed solution is a possible fix though rough. The challenge is that the outbound gateway ips are going to be the same so the router would need something else to know how to route packets, especially if you want some traffic to route one way and other traffic to route another. Check out the pfsense documentation to see if there is an example of this maybe or information on marking packets or something similar.
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@ptyork said in Two Cable Modems w/ Same IP:
I'm trying to multi-WAN two Cable ISP's. Both have the same management IP (192.168.100.1). How can I have both coexist such that I can access the management GUI for both?
Honestly, why would you need to? Put them in bridge mode and forget they're there.
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@jarhead One reason - I have a Netgear modem that regularly needs to be rebooted because Comcast sucks :-)
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Just to be clear, you may not be able to change the Admin IP, but can you change the DHCP range? Changing the range may have the side effect of changing the Admin IP.
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Do you mind telling us what the exact modem model numbers are? I’d like to poke a bit for my own curiosity.
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@rcoleman-netgate hmm, I'm not at all aware of bridge mode or how it works. Network admin is a "hobby-in-progress" for me. I thought I was doing well with Multi-WAN and a gateway group set for failover.
I've had it working okay for a while, but I'm trying to swap out a rented modem with a purchased one. I THINK the WAN side of things will work okay (still need to call Xfinity to get the new modem authorized). Just the goofy need for static route to the GUI.
But if bridging mode is a better solution, then I'm eager to learn. Can you or @Jarhead point me to a page or tutorial that describes this setup option?
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@gabacho4 Arris SB8200 and Motorola MB8611.
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@ptyork Your best bet here is to google search the model number and "enable bridge mode" to see how to do it.
Ryan
Repeat, after me: MESH IS THE DEVIL! MESH IS THE DEVIL!
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@andyrh cable modems are a bit odd. The ISP assigns you an IP address from their own DHCP range. And at least on these, the admin IP is fixed. Printed on a sticker on the bottom. There truly are almost no configuration options on these. You're not even allowed to update your own firmware. Only the ISP can do that...yes...even for a modem that you own. DOCSIS is a weird world.
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@ptyork said in Two Cable Modems w/ Same IP:
The ISP assigns you an IP address from their own DHCP range.
Yes but the modem management IP (the RFC1918 one) is not assigned out of an ISP DHCP pool
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@rcoleman-netgate ah, I think these ARE in bridge mode (vs. router mode). I was thinking you were referring to something to configure with pfSense needing to bridge two WAN ports or something.
Okay, then, yes. It sounds like I have the configuration pretty much as you describe. I just have to use the 'inelegant' solution of manually switching which of my WAN ports gets packets addressed to 192.168.100.1. Bummer, but far from the end of the world.
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@ptyork Then you need to do specific policy-based-routing to talk to a system. You can't talk to both at the same time from the same machine, basically. You put a rule on your LAN (or the interface your computer is on) that routes 192.168.100.1 out a specific gateway.
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@rcoleman-netgate thanks for the help. I think I understand. I can either toggle the static route between interfaces as I have it now or do as you suggest and set up PBR such that I can hit a different modem depending on which computer I access it from. Neither is a great solution, but either can work. Would be cool if there were some kind of NAT policy that could handle this, but I know it's a very fringe case and not worth really spending any development effort on.
Thanks to everyone for your help!!
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@ptyork said in Two Cable Modems w/ Same IP:
Would be cool if there were some kind of NAT policy that could handle this
Basically that's what the PBR is.
You could have one work from a wireless VLAN and one from a wired VLAN -- that's the suggestion I made to the last person that asked about it. -
@rcoleman-netgate understood. I just meant a way of translating and forwarding one IP address (e.g., 192.168.1.2) to another on a specific port (e.g., 192.168.100.1 on WAN2). So not a source-based policy, but one that could work from any LAN source.
Like I said, sounds like this is an edge case. Existing solutions can also work. Thanks again!
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You can try to use NAT like 192.168.101.1 to WAN2 and translate it do destination 192.168.100.1.
