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VPN subnet advice please

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rzj

IS-IT--Management
Nov 17, 2008
2
GB
I have two Draytek 2930Vn firewall routers and I'm trying to setup a LAN to LAN VPN between home and office.

Each Draytek router is connected to a Netgear ADSL modem router which also has wireless clients on the RED side of my firewall routers.

Both ADSL routers have local IP range 192.168.1.x then my green networks inside the Draytek's will be 192.168.2.x and maybe .3.x but maybe not.

I'm assuming I need to set the ADSL routers to port forward the traffic on port 1723 to my Drayteks.

Any advice on that bit welcome!

Now to the green subnetting...

General advice seems to be to have the 2 LANs on different class-C subnets, even to put one on 10.x.x.x , I assume this is to avoid IP conflicts, which I think I can get around by allocating any fixed IPs and DHCP ranges carefully.

In the past (before attempting VPN) I've tried to use 192.168.1.x and 192.168.2.x on the same physical network and set the netmask to 255.255.252.0 throughout so that I expected everything to be mutually visible locally.

I found that although manual stuff and Linux worked fine, some Microsoft stuff, and various devices like NAS and Printers didn't - I think because either the drivers or firmware assumes 255.255.255.0 or maybe because they scan for valid devices but only scan the last octet from 0 to 255 and don't do the 10-bit range I specify.

To avoid these problems I'd like to split my network so that home is 192.168.2.1-127 and work is 192.168.2.129-255

Then I can set the Vigors to the appropriate DHCP ranges, with some space fixed in each range as well.

My question's:
1) Can I do this?
2) In the LAN setup at each end should the netmask be 255.255.255.0 or 255.255.255.128
3) Similarly in VPN setup for the Draytek you have to set the remote network's IP range and netmask, the IP range is just specified in examples as xxx.xxx.xxx.0 I presume the remote network IP for the work network viewed from the home router should be 192.168.2.128, but again what should the netmask be? x.x.x.0 or .128 ?

4) If the view is that I should use 192.168.2.x and (say) .3.x then how do I make my 192.168.2.?? network printers and network drives visible to my 192.168.3.?? PC's?

5) Am I right in concluding that networks that are wider than 255.255.255.0 have problems with devices discovering each other (printers, network drives, UPNP, Microsoft file sharing etc)?

6) Dumb question - what traffic actually appears on both sides of the VPN? is it everything in both IP ranges, somehow when my HP printer gets a new IP from DHCP, all the PC's know what it is (although the Canon one doesn't!!), how would this get across the VPN if the printer's on 192.168.2.x and some clients are on 192.168.3.x

I have searched for info on this, but most info seems to be for big networks with lots of subnets, or it's basic explanation without going into the details.

I don't really understand the mechanisms involved in handling submasks and traffic routing - I kind of assume that if a PC is tring to access a target IP outside it's masked subnet then it routes the request to the gateway. And then that VPN sort of overrides this so traffic is grabbed by the router and passed on even though the sender doesn't force it to be routed - is this anywhere close to correct?

If anyone can point me at a primer that will explain what actually happens at the various boundaries in terms of which addresses pass across routers, NAT, VPN, which will go to the internet and which are local only that would be good!



Thanks,
Ray
 
I have had no luck VPNing through a NAT router, ever. So far as I know, you have to have a real internet WAN IP address.

I tried to remain child-like, all I acheived was childish.
 
Sorry, all my VPNs were router to router IPSec using consumer gear.

Linksys RV042 and WRV210
Netopia 3347NWG

I tried to remain child-like, all I acheived was childish.
 
Actually, I can park the NAT issue for now. It's just an extra level of complexity that will confuse things. I can always try to make it work later. a bit of reconfiguration at both ends and each router can "own" the WAN IP address. I was just being lazy about the wireless clients, but the draytek's have dual LAN so I can give the wireless routers an isolated branch of the network.

So, back to my main issue - I don't fully understand the mechanisms of subnetting, routing, gateways, and how VPN affects them.

I know how subnets are set up, but I'd like an idiot's guide to what actually happens to the packets in the network - it seems from experience that it is really difficult to get two devices to see each other unless they're on the same 255.255.255.0 subnet. When does the "gateway" IP get used - is it the sender that decides to use it?

I'm sure someone must have written a guide to the mechanisms involved in all this, but I can't find one.

With a VPN active is all traffic from both sides visible on the other side?

Is there a reason for different subnets on each end of a VPN other than IP conflicts - which I can fix by allocation of DHCP ranges?


Thanks,
Ray
 
Using my gear, the VPN 'routing' does not show in the routing tables.
If the IP address you are going to does not 'exceed' your subnet mask, that packet will never go to the router to be VPNed (or routed).

If it is a 255.255.255.0 mask, and I send a packet from 192.168.1.100 to 192.168.1.101, the router never knows, never cares. (if it includes a 4 port switch, the the switch portion knows, but not the router portion of the box)

If I send a packet from 192.168.1.100 to 192.168.2.100 and I have a VPN to 192.168.2.0 then the VPN part of the router kicks in and sends the encrypted packet to the other router to decrypt and send to 192.168.2.100

If I send a packet from 192.168.1.100 to 67.139.134.238, then the Router kicks in and sends the packet to the internet, eventually winding up at
All because I 'exceeded' the subnet mask, 255.255.255 means any 192.168.1.x address does not wake the router, anything outside that does. The PC sends to the router asking it to send it on.

I tried to remain child-like, all I acheived was childish.
 
hi guys how r u all doing? i need help i am using a EVDO 3g modem to use internet at home but at my office i have a vpn connection with enables me to log in to the domain and connect to exchange server and also the internet. now even if i connect to my modem i can still connect to the internet but my credit finishes very quickly how can i bypass vpn connection? what i mean is i want to use my vpn as internet connection so that my modem credit doesnt finish my vpn is 41.204.128.148 i have a domain user and pass how can you help please i wanna dial up on my modem then dial on vpn but use the office VPN connection without finnishing my credit many thanks asger@zantel.com 255 774 004004 please get back to me i appreciate alot
 
hi guys how r u all doing? i need help i am using a EVDO 3g modem to use internet at home but at my office i have a vpn connection with enables me to log in to the domain and connect to exchange server and also the internet. now even if i connect to my modem i can still connect to the internet but my credit finishes very quickly how can i bypass vpn connection? what i mean is i want to use my vpn as internet connection so that my modem credit doesnt finish my vpn is 41.204.128.148 i have a domain user and pass how can you help please i wanna dial up on my modem then dial on vpn but use the office VPN connection without finnishing my credit many thanks asger@zantel.com 255 774 004004 please get back to me i appreciate alot
 
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