Re: RRAS ip routing and ISA
- From: "Bill Grant" <not.available@online>
- Date: Sat, 22 Aug 2009 13:05:19 +1000
"bingyeo" <bingyeo@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:778D7D5D-2A74-4584-943F-BE8FE44E3CE2@xxxxxxxxxxxxxxxx
"Bill Grant" wrote:
Here are a few things to consider.
1. You can run two subnets on one physical switch, but it is not efficient.
Although the machines are connected to the same switch, machines in one
subnet cannot communicate directly with machines in the other subnet. They
must communicate through a router. These are usually confusingly called
virtual networks.
2. You cannot really run two DHCP servers on the same switch. DHCP works on
broadcasts, so there is no way to discriminate. If a machine broadcasts a
discover message, both DHCP servers will respond and the client will accept
whichever offer it receives first.
3. You don't really need the DHCP server to be standalone. You can run both
scopes on the same DHCP server, as long as your network is configured
correctly. The router between the subnets will forward the requests to the
DHCP server.
4. Unless you can see a way to configure this using VLANs, get an additional
switch and run each subnet on its own switch.
5. I would not run DNS and/or DHCP on a machine running as a router.
6. I found your proposed routing scheme a bit strange. It seemed to be aimed
at NAT routing rather than using the proxy service in ISA. In any case this
setup would not achieve your stated aim. All machines in the new subnet
would be able to see all machines in the existing subnet and vice versa.
7. To isolate one subnet, you would need to reverse your setup. The subnet
which could access the Internet but not the second subnet would need to be
directly connected to the ISA server. The second subnet would then be
connected to this subnet with a RRAS/NAT router. This simplifies the routing
but also means that machines in subnet 1 cannot connect to machines in
subnet 2 (because they are on the public side of the NAT). The setup would
look like this.
Internet
|
ISA
10.10.10.7
|
limited subnet
10.10.10 x dg 10.10.10.7
|
10.10.10.250 dg 10.10.10.7
RRAS/NAT
10.10.11.254 dg blank
|
10.10.11.x dg 10.10.11.254
You do not need any static routes. Because of NAT, all traffic from the
10.10.11 subnet uses the NAT router's 10.10.10 IP address in the 10.10.10
subnet. All traffic is automatically routed back to the NAT router, which
delivers the traffic in the 10.10.11 subnet. I haven't tested it (an I would
not do it myself), but this setup should run even on one switch.
Hi Bill, appreciate your reply.
Let me try to explain clearer my requirements.
10 subnet is our office network, running AD, DNS and DHCP for office use,
and connect via ISA to the internet.
We would like to provide internet access to external users who are not part
of the company, which is why the new subnet must have only access to ISA and
nothing else from the 10 subnet.
This is the reason why I am trying to run a separate standalone DHCP and DNS
servers, to reduce exposure of corporate resources to the 11 subnet as far as
possible.
Due to budget and hardware constraints, I am trying to work something out
with what I currently have to fulfil my requirements without additional costs.
Right now, the current setup is
Internet
|
ISA
10.10.10.7
|
limited subnet
10.10.10 x dg 10.10.10.7
1. You can run two subnets on one physical switch, but it is not efficient.I understand this point, which is why I have configured a server with 2 NICs
Although the machines are connected to the same switch, machines in one
subnet cannot communicate directly with machines in the other subnet. They
must communicate through a router. These are usually confusingly called
virtual networks.
with LAN routing on RRAS. However, the problem is that I am not able to
communicate from 10 subnet to 11 subnet and vice versa, and I do not know
where the problem lies. Do I need to configure static routes in RRAS?
2. You cannot really run two DHCP servers on the same switch. DHCP works onDoes this mean that the only way to go is either additional switches or
broadcasts, so there is no way to discriminate. If a machine broadcasts a
discover message, both DHCP servers will respond and the client will accept
whichever offer it receives first.
configuring VLANs on the switch?
I would like to avoid the complexity of VLAN configuration.
3. You don't really need the DHCP server to be standalone. You can run both
scopes on the same DHCP server, as long as your network is configured
correctly. The router between the subnets will forward the requests to the
DHCP server.
See the starting lines of this post, would like to separate server roles for
each subnet.
See point 2.
4. Unless you can see a way to configure this using VLANs, get an additional
switch and run each subnet on its own switch.
5. I would not run DNS and/or DHCP on a machine running as a router.Ok, got it. Would running DNS and DHCP on 1 machine and another as a router
be better?
6. I found your proposed routing scheme a bit strange. It seemed to be aimed
at NAT routing rather than using the proxy service in ISA. In any case this
setup would not achieve your stated aim. All machines in the new subnet
would be able to see all machines in the existing subnet and vice versa.
7. To isolate one subnet, you would need to reverse your setup. The subnet
which could access the Internet but not the second subnet would need to be
directly connected to the ISA server. The second subnet would then be
connected to this subnet with a RRAS/NAT router. This simplifies the routing
but also means that machines in subnet 1 cannot connect to machines in
subnet 2 (because they are on the public side of the NAT). The setup would
look like this.
Internet
|
ISA
10.10.10.7
|
limited subnet
10.10.10 x dg 10.10.10.7
|
10.10.10.250 dg 10.10.10.7
RRAS/NAT
10.10.11.254 dg blank
|
10.10.11.x dg 10.10.11.254
You do not need any static routes. Because of NAT, all traffic from the
10.10.11 subnet uses the NAT router's 10.10.10 IP address in the 10.10.10
subnet. All traffic is automatically routed back to the NAT router, which
delivers the traffic in the 10.10.11 subnet. I haven't tested it (an I would
not do it myself), but this setup should run even on one switch.
What do you mean by 'directly connected to the ISA server.'?
The 10 subnet is connected to the same switch as ISA currently.
I am not entirely sure of the difference between NAT routing and using ISA
as a proxy server. I configured ISA as an Edge firewall and configured WPAD
in DHCP and DNS for autodiscovery for our office users.
From your diagram, does this mean that I have to configure NAT on RRAs
rather than LAN routing?
Cheers
Yes. If you configure RRAS as a NAT router, you do not need additional routing. NAT takes care of it by doing address translation. All traffic from the 10.10.11 subnet uses the NAT router's 10.10.10 IP address in the 10.10.10 subnet. Traffic going beyond this network comes back to the NAT router, which has tables set up so it can forward the reply to the correct machine on the 10.10.11 subnet.
If you use LAN routing, you need extra routing on the ISA server so that it knows where the 10.10.11 subnet is and how to reach it. The other disadvantage is that any machine in either subnet can see any machine in the other, which you said you did not want.
.
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