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Posted by Fred Marshall on July 2, 2007, 1:22 am
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"Mike Drechsler - SPAM PROTECTED EMAIL"
> Fred Marshall wrote:
>> "Mike Drechsler - SPAM PROTECTED EMAIL"
>>> Fred Marshall wrote:
>>>> I'm using RV042s for VPNs and general routing. Often there are
>>>> questions but seem to be no place for answers.
>>>>
>>>> For example: if one is using an RV042 for VPN, then what affect does
>>>> the routing table have on the VPN packets?
>>>>
>>>> Is there any place where this sort of thing is reasonably described?
>>>> Or, is the answer to this one question supposed to be obvious?
>>>>
>>>> Fred
>>> apparently it's supposed to be obvious.
>>>
>>> It does help to have prior experience with setting up IPSEC VPN tunnels
>>> and a good understanding of how it works.
>>>
>>> Routing tables will have limited use when you are trying to move
>>> traffic. A routing table will not affect the contents or intended
>>> contents of an encrypted packet.
>>>
>>> If you want to give an example of what you are attempting to setup then
>>> perhaps you will find some help.
>>
>> Mike,
>>
>> thanks for the reply.
>>
>> I can envision the VPN "block" running in series or in parallel with the
>> routing table "block". In the first case, on the incoming /
>> post-decryption end. In the second case, totally independent. Not much
>> else makes sense to me but I sure can be enlightened.
>>
>> What I've been trying to do is like this:
>>
>> Launch a packet destined for a "foreign" private subnet.
>> Route such packets at their source to the LAN address of the RV042 VPN
>> router.
>> From there over the internet.
>> When the packet is received at the other end of the tunnel, it will still
>> be destined for a "foreign" private subnet.
>> i.e. the packet is destined neither for the local nor the remote subnet.
>>
>> So, I add a route on the receiving RV042 that points such packets to a
>> gateway on the remote LAN. If this works then such packets should be
>> directed to that gateway. But, it doesn't seem to work.
>>
>> Here are the addresses involved:
>>
>> Source: 192.168.113.130 Destination 192.168.1.4
>> 255.255.255.224 Route for destination: 192.168.113.157 the
>> RV042 VPN
>>
>> (I guess at this point there is no route in the RV042 for this address
>> range. Can the RV042 routing table route packets into its own VPN? I
>> don't see how). So, this could be a problem I guess. The destination
>> *is not* in the VPN remote LAN range.
>>
>> (internet)
>>
>> RV042 VPN 192.168.113.198 w/Route: 192.168.1.0 /24 > 192.168.113.254
>> 255.255.255.192 255.255.255.192
>> has port
>> on:192.168.1.0/24
>>
>> It appears that the packets don't arrive at the destined router on the
>> remote LAN.
>>
>> If the RV042 routing table does not deal with unencrypted packets coming
>> out of the VPN then this method wouldn't be expected to work. It would
>> really help to know what to expect without running a bunch of
>> experiments.
>>
>> Or, maybe the VPN-initiating RV042 doesn't accept packets thus destined -
>> as they are on different subnets? My confusion here is that there's a
>> remotely managed Cisco router on site that does pretty much the same
>> thing. It takes the packets and routes them to appropriate ports just
>> fine (and for a lot more $$).
>>
>> Fred
>>
>>
>
>
> The VPN endpoints will not encrypt any traffic that is not included in a
> security association. In other words the range of IP's you are trying to
> reach and the range of IP's the traffic is coming from MUST be included in
> the subnets for the encrypted tunnel. You cannot use the encrypted tunnel
> as a route where arbitrary packets can enter on one side and exit the
> other side. IPSEC is meant as an end to end ecryption mechanism so it
> will refuse any traffic that is not specifically included in the subnet
> ranges that were used to build to the tunnel.
>
> So I'm looking at the VPN Tunnel settings on an RV082 which I assume has
> the same user interface as the rv042. Where it says Local and remote
> security group type, IP address, and subnet mask. These will define the
> range of IP's that will go through the tunnel connection. The solution
> would be to either create a larger range of IP's to include in the local
> and remote subnets or if that is not practical then create a second tunnel
> with a different set of remote and local IP's that will be sent encrypted
> to the other router.
>
> I'm sorry I cannot comment on your specific examples. I have no clue what
> you are trying to do with the IP's you listed, it's simply not clear to me
> the way you wrote things down.
>
> Here is a simple example.
>
> So the basic case is you create a VPN tunnel that connects the
> 192.168.100.0/24 subnet in your estern office with the 192.168.200.0/24
> subnet on the other site at your western office. This is the simple case
> and you would simply follow the examples in the documentation.
>
> 192.168.100.0/24(east)->RV042->Internet<-RV042<-192.168.200.0/24(west)
>
>
> Now you are saying that you have multiple subnets in each office and you
> want to route the traffic to the tunnel. So you are assuming that you can
> just create a static routing table entry to point the traffic to the IP of
> the router on the other end of the tunnel and you expect that the packet
> would end up inside the tunnel as a result
>
> So you have built a tunnel using the simple case example above.
> Now you create a static route in the east that looks something like this:
>
> You want:
> 192.168.101.0/24->192.168.100.1->INTERNET->192.168.200.1->192.168.201.0/24
>
> On the east side you create a static route that says Destination ip:
> 192.168.201.0/24 (a subnet in the other office) uses gateway 192.168.200.1
> (Internal IP of the router on the other site)
> On the west side you create a similar static route that says Destination
> ip: 192.168.101.0/24 uses gateway 192.168.100.1
>
> But this will not work because these source and destination IP's are not
> part of the original subnets of the tunnel they will not be encrypted or
> sent across the tunnel.
>
> What you need to do is create 2 parallel tunnels that go between the same
> routers with different local and remote subnets.
> 192.168.100.0/24(east)->RV042->Internet<-RV042<-192.168.200.0/24(west)
> 192.168.101.0/24(east)->RV042->Internet<-RV042<-192.168.201.0/24(west)
>
> Also the subnet definitions of the tunnel do not need to exactly match the
> LAN subnet on the other side. You can make these larger as long as the
> range of IP's in the larger subnet range is still correct for the remote
> site. Also you can use expanded subnet ranges to create hub and spoke
> configurations where one central site creates single tunnels to each
> branch office and if one branch office wants to communicate with another
> branch office then the traffic flows to the central site first where it is
> redirected to another tunnel to the second branch site. This requires good
> planning but it saves you from creating a tangled mess of tunnels for
> sites that rarely need to communicate directly.
>
> A good example would be:
>
> Central site: 192.168.100.0/24
> Branch 1: 192.168.110.0/24
> Branch 2: 192.168.120.0/24
> Branch 3: 192.168.130.0/24
> etc.
>
> To create a hub and spoke configuration you would create a tunnel like
> this:
> Local security group: 192.168.110.0/24
> Remote security group: 192.168.0.0/16 (The remote range is for
> 192.168.0.0-192.168.255.255)
>
> So now you send a packet from branch 1 to branch 2.
> eg: source: 192.168.110.15 -> dst: 192.168.120.55
>
> So this causes your router to send any traffic that is not for the local
> lan on a private IP in the 192.168.0.0 range off through the encrypted
> tunnel. When it reaches the other end that central router will evaluate
> the packet after decrypting it and if it is for it's local lan it will
> forward it to the LAN. If not then it will evaluate the packet to see if
> it matches another tunnel. It will find that a tunnel with a remote
> subnet of 192.168.120.0/24 exists and that this packet also matches the
> local security group definition so it is to be encrypted in the tunnel. It
> resends the packet to branch 2. The branch 2 router decrypts the packed
> and finds the destination is for the local subnet so it forwards it to
> it's LAN.
>
> You can think of these tunnel definitions as another layer of routing that
> happens before the traditional routing table is evaluated.
Mike,
Thanks.
Well the point of my question was about how the RV042 works. I'm becoming
rather convinced that if it's being used as a VPN device then the static
routes one might enter will have no affect.
Fred
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