[ale] 10.1.10.1 Comcast access from local LAN? (Slightly OT BUT there is Ubuntu AND PI involved!)

[Derek Atkins]

HI,

Youre ascii art is hard to read, so I can't tell what's where.
But basically, no, what SHOULD be happening is that your RV180 would NAT
your 192.168 network to its 50.248 address.  then it will send a request
to 10.1 -- the DPC3939 might not allow that.

I think it very unlikely that the Comcast device is seeing the packet
coming from 192.168.

More likely it's blocking access from the 50.248 to the 10.1 address.

Here's something to try:  Can you ADD a 10.1. address to the Comcast side
of the RV180?  In other words, let it have the 50.248 address as the
default address, but also add a static address of 10.1.10.X?  And ensure
it properly NAT's from 192.168 to 10.1.

-derek


On Fri, February 5, 2021 11:45 am, Neal Rhodes via Ale wrote:
> Our church has a Business Comcast DPC3939 connected to Our little Cisco
> RV 180 VPN.
>
> The Comcast has a local IP of 10.1.10.1, and the WAN Static Address of
> 50.248.230.105.
>
> Our Cisco router has a WAN address of 50.248.230.106, and it supports a
> 192.168.1.X network behind that, which is where everything on the LAN
> lives.
>
> INTERNET==>Comcast DPC3939 <===>Our Cisco RV180VPN<====Our 192.168.1.X
> LAN <==JackTrip Raspberry Pi Virtual Studio
>                            50.248.230.105                  50.248.230.106
>                                                           <== Everything
> else on the LAN
>                             10.1.10.1
>                                    |== Ubuntu JackTrip Audio Server
>                                            10.1.10.91
>                                            Port Forwarding 4464, UDP
> 61002-62000
>
> We really need to do a couple of things:
> - our office administrators need to occasionally be able to http access
> the Comcast router from our 192.168.1.X LAN.  They cannot.  Any attempt
> times out.  (Fun fact: you CAN http to 50.248.230.105, and get a login
> response, BUT the correct userid/password will result in a Password
> failure.  It only allows login from the 10.1.10.1 address.)
> - we need for ME to be able to occassionally get an ssh session from an
> office PC TO the Ubuntu server.   Similar challenge I think.
> - The Raspberry Pi Virtual Studio box in the sanctuary needs to connect
> to the Ubuntu server on port 4464.   I think it can hit the external
> address of the Comcast router for that.   I've got that port forwarding
> all working now at home with a UVerse router.
>
> We can access the Comcast Router as http://10.1.10.1 IF we go downstairs
> to the furnace room and plug into the LAN ports on the DPC3939.  The PC
> will then get a 10.1.10.X address.
>
> Now, when I look at the DPC3939, I see no evidence that it has a static
> route for our LAN.  So, when someone on, say 192.168.1.145 puts
> 10.1.10.1 in their browser, the PC hands it to our Cisco router, it
> knows it's not on our LAN, so it hands it to its gateway: the DPC3939.
>
> And then I THINK the DPC3939 then says, "I don't know where to send
> 192.168.1.145" and so it times out.
>
> I THINK the Comcast router needs a static route that says 192.168.1.X is
> behind our Cisco router: 50.248.230.106.
>
> Am I thinking right?  I don't mind stuffing in the route myself, but I
> asked Comcast first, since it's their equipment.   Tier 1 said, "no
> that's not possible".  Tier 3 response was:
>
> _1- you need to know, in order for two local networks to communicate
> they have to be in the same lan scheme, either both 192.168.x.x or
> 10.1.x.x_
>
> _2-  My suggestion is to change the local IP scheme for Comcast
> modem/router to match the other router _
> _192.168.1.X_
> _ _
> _3- Make sure the IP scope of the modem is not conflicting with the
> other router._
> _ _
> _For example if the other router IP scope is from 192.168.1.1 to
> 192.168.1.100 then make the modem DHCP  192.168.1.101 to 192.168.1.200.
> Same lan scheme different IP scope to avoid future issues._
>
> The Tier 3 response sounds insane to me; if I'm on 192.168.1.145, and I
> want to send data to 192.168.1.4, my IP stack will just put it out on
> the LAN wire.   The Comcast router is never going to see that,  'cause
> it's connected to the WAN port on our router.    The only way my gateway
> would get involved is when a workstation knows that the destination is
> NOT on the local network, and hence the packet needs to get passed to
> the gateway.  The Tier 3 response also seems to open up all kinds of
> security issues if it in fact worked; then a compromise to anything on
> the Comcast side could easily bleed into our LAN.
>
> What is kinda weird to me is that at home this "just works".  I have an
> AT&T Uverse router which provides 192.168.1.X.  I have a Sonicwall VPN
> router plugged into that, which provides a LAN of 192.168.100.X.   The
> linux and PC devices are on the 100.X network.   There are a few
> expendable devices and IOT on the 1.1 network.    I can ssh and http
> from the 100.1 network to hosts on the 1.1 network; but of course they
> cannot go the other way.    I didn't do anything for this to happen.
> Did the routers exchange BGP and just figure that out?
>
> Regards,
>
> Neal Rhodes_______________________________________________
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> Ale at ale.org
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-- 
       Derek Atkins                 617-623-3745
       derek at ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant