Networking :: Routing Subnet Over GRE Tunnel

Mar 1, 2011

Im trying to configure a GRE over IPSec connection between two subnets. The IPSec tunnel is opened and now I want to add a GRE tunnel over it.So, what I didn't understand is why I can't route my subnet over the tunnel, once the only route I have there says that it should route the tunnel IP over the GRE01 interface. Any hint? Thanks.

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Networking :: Routing Between Two NICS On The Same Subnet?

Aug 2, 2010

I'm trying to work out how to route all traffic destined for the internet from all devices connected to eth0 to a wireless router access point via wlan0 on my Slackware box. I also have dhcpd providing ip addresses on the same subnet to any device connected to both eth0 and wlan0.


____________ ____________
[ ]=============> (wifi) ==============>[ Router / ]
|Workstations| __________ |Access Point|
[____________]==>(eth0)==>[ ]<==(wlan0)==>[____________]| Server |

If I connect to the router/access point via wireless or directly to the Server via a crossover cable I can obtain an ip address from dhcpd, so that works. As far as I can see I just need to how to route between eth0 and wlan0 then I can provide internet access to those devices!



eth0 Link encap:Ethernet HWaddr **:**:**:**:**:**
inet addr: Bcast: Mask:
inet6 addr: fe80::201:2eff:fe27:aea3/64 Scope:Link


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General :: Windows - Routing Everything Except A Certain IP Range Through An OpenVPN Tunnel?

Aug 31, 2011

I've been working with my OpenVPN server for a while, and I have a rather interesting problem. I need to redirect all client traffic through the tunnel except for a couple IP's that need to be resolvable locally. The way I'm doing this is pushing these routes from the server:

Server 'PUSH' directives

push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS"
push "dhcp-option DNS"

I'm seeing that translating into these Windows routes:

Windows routes occurring

Wed Aug 31 15:14:35 2011 PUSH: Received control message: 'PUSH_REPLY,redirect-gateway def1 bypass-dhcp,dhcp-option DNS,dhcp-option DNS,route,topology net30,ping 5,ping-restart 30,ifconfig'
Wed Aug 31 15:14:35 2011 ROUTE default_gateway=

Wed Aug 31 15:14:40 2011 C:WINDOWSsystem32
oute.exe ADD 199.[*.*.*] MASK
Wed Aug 31 15:14:40 2011 C:WINDOWSsystem32
oute.exe ADD MASK
Wed Aug 31 15:14:40 2011 C:WINDOWSsystem32
oute.exe ADD MASK
Wed Aug 31 15:14:40 2011 C:WINDOWSsystem32
oute.exe ADD MASK

I've hidden my server's IP beginning with 199 for security purposes.What I've gathered.I'm assuming that is a kind of code for "everything," so I'm not sure how I could get this to work, but the general idea is that I need a specific IP range (172.16.*) to be resolvable on the LOCAL NETWORK (of the client) meaning it does not go through the VPN tunnel and the client can connect to 172.16.* locally.Is this possible? Routes can be executed through the command line, server "push" or client config options. Any way to get this to work while still routing other traffic through would do, really.

Additional Info: I have the server running on Debian 64-bit and the client running on Windows 7 (although Vista needs to work as well).Client/server configs can be provided if needed.

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Networking :: VLAN With 2 Router And 2 Subnet - Is Device In Different Subnet Works

Jul 22, 2011

I have TWO L3 + router switch (say switch1 and switch2). I created VLAN100 with VLAN ID 100 in both the switches. I created router in Switch1. I created router in Switch2. Switch1 is connected with 1.x/24 PCs. PCs are configured with 1.1 gateway. Switch2 is connected with 2.x/24 PCs. PCs are configured with 2.1 gateway. Both Switch1 and switch2 are connected by a trunk to carry VLAN100 data.

1)I have few PCs of 1.x connected to say Switch1 Is it possible for PC with IP to ping PC with IP are the configuration required in both switches to make them communicate ? All the device in both the subnets should ping/communicate with each other.

2)Move PC ( to switch2. Move PC ( switch1.What will happen when PC(1.100) ping (2.100) and vice versa?What will happen when PC(say 1.80 in switch1) pings PC (say 1.100 in switch2) and vice versa? What will happen when PC(say 1.80 in switch1) pings PC (say 2.100 in switch1) and vice versa?

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Networking :: Can't Browse Computer Of One Subnet From Another Subnet

Jul 4, 2011

I installed Redhat Enterprise linux server5. it has two LAN card and two subnet connected to these two LAN card. i can browse network from these two network easily. But i created VLAN on one network card.Now i cant browse network from these VLAN subnet.

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Networking :: Insert Routing Data Into The Routing Table Doesn't Work?

Apr 6, 2010

I have a firewall, this consists of three NIC's:

Code: eth0[] eth1[] and eth2[]

I am trying to ping eth0 from eth2, but I am not able to succesfully get a response from pinging the device, I am using:

Code: ping -I eth2

I have tried to insert routing data into the routing table, but it still doesn't work

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Networking :: 2 Nics In Same Subnet?

Jan 8, 2010

I have 2 x PCs and a NAS. Both PCs have 2x NICS. PC connectivity to Internet is via an ADSL router. Current config: Thus far (by choice) I've used static IPs in the 192.168.168.x range for my internal network, connecting all PCs and NAS via a jumbo frame enabled gigabit switch. This has facilitated moving data between the PCs and the NAS at high-speed. As both PCs also required Internet access from time to time, both are also connected to the ADSL router using the 2nd NIC and using subnet 192.168.1.x. I'm sure some of you are shaking your heads by now, but it works well and has been entirely hassle free.

However, I've an app running on the NAS that I'm keen to get Internet connected also. As my existing network devices are not using DHCP I figured the simplest method would be to change my ADSL router configuration such that it is in the same 192.168.168.x subnet, change its DHCP server settings to serve IPs in the same subnet (but in a restricted range I know won't cause any conflicts with the static IPs) and problem solved. On changing the ADSL router confiruration with all machines already booted up and configured as described above, everything worked. All devices could see one another, and access the Internet. On later rebooting the system this no longer works

- Internet access is fine but PCs don't see one another or the NAS. If I disconnect the ADSL Router from the PCs then all devices see one another again.

- Does having 2x NICS on a single device each assigned unique IPs in the same subnet create an issue and can it be overcome? I'd like to overcome it because making one of my PCs the gateway forces me to have it on anytime another device needs access.

- If I'm forced to use Internet connection sharing with one PC on the network connected to the router, how do I best configure this?

- One of the things I need to retain is gigabit connectivity between the PCs and PCs and the NAS (currently achieved by 192.168.168.x subnet being linked via gigabit switch).

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Networking :: Access IP From Outside Subnet

Dec 26, 2010

I am trying to make Apache web server, it's work but cannot be browsed outside my subnet.I am on huge LAN network, not sure how it works, know it have TL-SL2428WEB Smart Switches and probably some kind of DHCP, every user have maximum 64KB, just plug UTP cable, and I have static address on that subnet like: "" witch I know from Java NetworkInteface class or when I try to update IP on my Dynamic DNS account with ez-ipupdate, but my subnet is connected to Web with another IP like "my.isp.provider.ip" witch I get from and I check that is my Cable ISP provider web IP. It is possible that there is more subnet layers between these two IP.Problem occurs when I try to access to my web site from another computer. When I set dyndns host name to be or use localhost everything works fine from my computer, I can access my web site, Apache work, I can use ssh. To illustrate you it work like this: Go to DNS server, find my host name, get my "" and say "This is actually my localhost IP, no need to go on Web, lets loopback". But when I try from another computer even from my college's computer on same subnet it don't succeed. When host name is set on "my.isp.provider.ip" of course nothing works.

We, users of LAN, don't have access to our LAN nor we have admin. For example sometimes we stuck without net and we cannot even press reset button on switches or something like that, we have to wait for day to they, owner of LAN, order some professional to do that. It seems they are just user of Cable TV and IP, and they bay and install LAN without any kind of admin. Also, I use Fedora 13, with httpd, ssh and others packages that comes with Fedora 13 DVD. I know to write bash scripts, use yum, very good in C++ and Java, great programmer, but newbie in networking, , a very little Perl, html, web servers, I heard for DHCP, DNS, NAT, IP forwarding. How you see it is problem in my lack of knowledge about networking. I hope that I succeed to describe by problem with enough details. Please, try to help me. I be very graceful for any kind of help. Don't afraid to bomb my head with any kind of information hard to understand.

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Networking :: Gateway In Other Subnet

Jan 1, 2011

I've rent a server from a Germany data center,They use a single IP as their gateway that is not in range of my servers IP,Strangly server is working well and when I use 'route -n' command the gateway which is in other subnet appears properly./etc/sysconfig/network contains no gateway IP and I don't know how they set the default gateway while after reboot the gateway is the same, also the IP is static and there's now DHCP.I need to know how they did it so I can do the same on my VPSes.

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Fedora Networking :: Two NIC's Can Be Bridge Together Even Though They Are The SAME Subnet?

Aug 9, 2009

I have 2 NIC's in a box. One of them is external and doesn't matter for this question I don't think.

The other NIC is It hosts an iSCSI Target and SMB Share on my LAN. It's works great.

I have another PC that has NIC at and it hosts my DHCP (Scope: server for my LAN.

I have a hardware firewall at and it serves inet to the LAN on a different external connection.


I currently have a WAP (cheap p.o.s. netgear router in WAP mode that keeps overheating). I want to eliminate the WAP device and add a WiFi NIC to the Top PC above.

So, on the first system I would have:

NIC 1: External IP and External Gateway
NIC 2: Static IP
Proposed WiFi NIC 3: Static


If I bridge NIC 2 and NIC 3 like this:

# brctl addbr br0
# brctl addif br0 eth0
# brctl addif br0 eth1

Then I simply put the WiFi in Ad Hoc, will another WiFi in Ad Hoc (for example my laptop) be able to "see" (DHCP) & (Gateway) (via WiFI through the bridge to and on to the LAN)?

Also, can the two NIC's be bridge together even though they are the SAME subnet?

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Networking :: How Subnet Masking Works

Nov 15, 2010

I have read NUMEROUS tutorials and explanations on the net about this, but they all seem to assume an informed understanding of IP networking. I have limited knowledge (basically I know how to set up my own home network and use the normal commands for troubleshooting.).I am doing a project at work which requires networking our new store with our original store (throughA VPN).I am just trying to understand in the most basic way how sub netting and subnet masks work. I don't believe this is necessary knowledge for setting up the network via VPN, but I would just like to understand it and I feel like I will be prepared to study further. basically:

1. How does a network mask isolate a particular host on a network?
2. How does changing the mask allow for more addresses to be used?

For example, if my address is, say,, how does isolate my machine to receive traffic? I suppose what I am really not understanding is how it does this with more than one host on the network with the same mask.

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Networking :: Cannot Ping To Machine From Another Subnet?

Apr 23, 2010

I installed apache2 on my Ubuntu machine and I am trying to access the server from another subnet. The server is connected using ethernet and has a static ip address. I can ping from the server to any machine in the other subnet but non of the machine on that subnet can ping the server. iptables does not seem to be running


# service iptables status
iptables: unrecognized service

and its rules are


# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination


What is preventing my machine from being accessed from the other subnet?

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Networking :: Can't Set Default Gateway To Different Subnet / Do That?

Feb 3, 2011

This is slackware 12. I'm trying to share my internet connection (on eth0) with a computer connected to eth1.

eth0 is, eth1 is (different subnets).

But when I try to make eth1's default gateway the same as eth0's, see the error I get code...

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Networking :: Connecting To A Printer On Another Subnet

Aug 19, 2010

I have some trouble setting up a printer on my network. My network is divided so that all wired connections are in one subnet, while all wireless devices are in another. My printer is Canon MP640 and is connected via wireless. When I use the network printer scanner utility from Canon, it will only scan my wired subnet, and is thus unable to see the printer. I can ping the printer, so there is no problem with subnet segregation.

On my router, I have Debian and iptables. My initial thought was that I could somehow set iptables to just forward all packets to an address to my printer. This address, of course, wouldn't exist "physically". But I have no idea whether or not this is the right approach. A suggestion I received from a colleague was to set up forwarding of broadcast packets. However, I am unsure whether this will have an impact on the wired subnet. If any of you could conjure a magical iptables rule for this or have suggestions other than plugging the printer into the wired net

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Networking :: Default Gateway On Different Subnet?

Jan 8, 2010

I am in a big confusion and searching an answer to calm down my mind.I have my eth0 has following configuration

` ` `


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Networking :: Forward Reverse Dns Subnet?

Mar 25, 2010

I have the zone record which is working fine.

The NS for that zone is setup for my own name server.

I however would like to forward requests for to another name server. How would I do this?

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Networking :: Setting Up A Subnet On A Wireless Network?

Sep 13, 2010

I'm living at a friend's right now, and he's got a wireless access point in the house that I set my laptops wlan0 interface to route through the eth0 to my desktop. It's been working fine for internet sharing and internal networking ( ssh and ftp ) between the laptop and the desktop, but there's a problem with both subnets being able to communicate with each other, and I haven't been able to solve it with DNAT either.

The wireless access point is and has its own lan on of which my laptop is I setup the little subnet I created by routing with the laptop to and my desktop is With shorewall I can configure iptables to DNAT all of my ssh traffic destined to to, but the problem seems to occur when ssh on my desktop fails to connect rather than the DNAT failing.

Using iptraf I've seen that all of the routing does work properly, because I can see on the connection in iptraf that only the SYN packet is being sent from a 192.168.0.x address, there is no ACK packet sent back. I believe this is because in the connection dialog it always shows a 192.168.0.x ip as the source of the connection, but I don't have a route to from setup and I'm unsure of how to do so.

I'm pretty much in over my head because I don't know what is wrong, I thought it should work like this. Everything else from port configurations, to the configurations of the software itself seems fine so I don't think it's anything like that preventing a connection, but I can't think of what it would be aside from the lack of routing between each subnet.

Is there anyway to just add a route so that and can communicate with each other directly? I know there should be, I'm just not at all sure how it would be done.

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Networking :: Access Public IP From Local Subnet

Jan 22, 2011

does somebody know how dnsmasq / iptables need to be configured such that requests to my public IP from lan are correctly NAT'ed to the host that handles them? Currently my routing device treats them like "oh, these are anyway for me, gnam gnam" which actually doesn't work.Unfortunatly setting up NAT rules that redirect requests from my lan correctly as they are redirected from wan is an option I would like to use only if there is no other possibility.I would like some kind of solution that treats packets that are sent to my public IP as normal packets that are not looped back before they even get out. So they would need to be at least sent to the wan gateway where they are directed back where my firewall can successfully treat them like all other public requests.

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Networking :: ARP Does Not Resolve MAC Address Of Hosts On The Same Subnet?

Jul 26, 2011

I just changed my CentOS server from DHCP to static IP address. After the change, I cannot ping other hosts on the same subnet. (I can ping the CentOS itself).The IP address of CentOS is pinging (106 is on and other host can ping it), arp -a shows? ( at <incomplete> on eth0 It looks ARP cannot resolve MAC address of hosts

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Networking :: Dhcpd3: No Subnet Declarations For Eth0

Jul 17, 2010

Running on Debian Lenny, installed dhcpd with apt-get install dhcp3-server. Machine has two NICs: and

My /etc/dhcpd.conf:

subnet netmask {
option routers;


Trying to start dhcpd reports "no subnet declaration for eth0 (" and "no subnet declaration for eth1 (". Is dhcpd using /etc/dhcpd.conf, or do I have the wrong config file? If it's right, why is this failing?

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Networking :: Find Unused IP Address In Subnet?

Jul 25, 2011

I need to find myselfe unused IP address in some subnet.
How to determine that particular IP is ununsed in that subnet without asking network admin ?

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Networking :: Config DHCP For Multiple Subnet?

Jun 21, 2010

I have a network with multiple subnets from to using net-mask and one gateway I want to setup a dhcp server and wonder how should I config it? All the hosts in the network using the same net-mask and gateway.

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Networking :: Configuring Xen Bridge (2 VM Inside) Under Same Subnet

Apr 28, 2010

I have installed a Xen with 2 VM's inside. They are all under the same subnet. The Xen machine can see the outside network but both machines in it cannot.
How do I create the bridge correctly (to xenbr0 i guess) so it fixes this?

Here's what I tried: It's RHEL5.3
1. '/etc/sysconfig/network-scripts/ifcfg-eth0' is ok on both VM's
2. iptables service is disabled, system-config-network shows IP,DNS, GW are correct.
3. On the VM's the route -n shows the gw ip though I cannot ping it.
4. checked hosts.allow, hosts.
5. In '/etc/xen/xend-config.sxp' unmarked:
(network-script network-bridge)
(vif-script vif-bridge)
6. in xen/<images_location>/ I modified vm.cfg so vif = [ 'ip=' ] for one of my virtual machines.
7. I cannot however find '/etc/network/interfaces', can anyone advise if actually in my case it's the ifcfg-eth0?
8. I basically followed the Bridged Networking scenario in Xen Networking: [URL]

Ifconfig on the Xen Parent:
[root@XEN_PARENT]# ifconfig -a
eth0 Link encap:Ethernet HWaddr 00:50:56:8B:3A:E4
RX packets:130021 errors:0 dropped:0 overruns:0 frame:0
TX packets:75097 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:10315149 (9.8 MiB) TX bytes:12038346 (11.4 MiB)
Interrupt:17 Base address:0x2000 .....

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Networking :: Subnet - Network IP - Broadcast IP Calculation

Feb 14, 2010

I am basically from system side and often confused about the calculation of the IP addresses.Just i want to know that what how can i calculate the following of a IP Address:

(1) Available IP in a Network
(2) Broadcast IP
(3) Network Prefix or Net Mask

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CentOS 5 Networking :: Multiple NICs On The Same Subnet?

Mar 30, 2009

I have a motherboard which has 4 x 1Gbps Ethernet controllers. I would like to use it as a Gateway for my home network. I have a static IP from my ISP which I can use to configure eth0 (I haven't done it yet as the LE-565 is currently sitting behind my Netgear router until I've got DHCP working). I would like to use eth1, eth2 and eth3 for my LAN. How do I set things up so that DHCP is handing out IP addresses on the same subnet ( on all three interfaces?

P.S. I think what I'm asking is: how do I combine all 3 interfaces to behave like a switch (ie. just like my Netgear router)?

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CentOS 5 Networking :: VLAN And Gateway Outside Of Subnet?

Jan 12, 2011

My company hosts five Servers with CentOS 5 installed in a Data Center. The Data Center assigns a VLAN to each customer so that they can organize customers and also count traffic. The VLAN assigned to my company is in the form 62.103.X.X with a subnet mask so the IPs that we can use in our Servers are 13. The first IP in the VLAN (for example is the Gateway and the rest, that are calculated from the subnet mask, are assigned to servers( up to

The problem I have is that we have run out of IPs in our VLAN. We have used all IPs and we want some more. The Data Center can assign new IPs but not grow our VLAN IPs by expanding the subnet mask. So they gave us a new VLAN with some IPs (for example 62.104.X.X with a subnet mask They told me that I had to use as gateway the gateway of the first VLAN and assign the new IPs as usual. So I assigned to one of the CentOS 5 servers the IP and set the gateway to Unfortunately this did not work and we could not establish connectivity to the Internet.Is it possible to assign a gateway outside of the IPs that are in the subnet? Could it be a problem with the VLAN setup by the Data Center?

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Fedora Networking :: Multiple NICS In Same Machine In Same Subnet?

Dec 7, 2009

I have a program that attaches to an interface. I can run two copies of the program on two systems (each running one instance), connect it to a switch, say & In this configuration two instances of the program can communicate and everything is fine.Now, to reduce cost, it want to use only one system with two nics connected to the same switch, running two instances of the above program, each instance attached to two interfaces respectively on the system. I have the following settings:

eth1 Link encap:Ethernet HWaddr XXXXXXXXXXXXXXX
inet addr: Bcast: Mask:


However I cannot ping one from the other.

Neither "ping -I eth1" nor "ping -I eth2" works.

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Ubuntu Networking :: Multiple Ipv6 Routers On A Subnet?

May 6, 2011

I have a 6to4 tunnel running on Ethernet (subnet 2002:ad4c:16cc:1) without problem. It runs radvd and announces a default route back to the Internet like this: "default via fe80::6a7f:74ff:fe0a:fbec dev br0"

On this same Ethernet I have a Linux plugbox (fe80::225:31ff:fe01:cc) which is a gateway to a network of IPv6 enabled sensors. I've assigned this second subnet 2002:ad4c:16cc:2. How do I get the plugbox to announce "2002:ad4c:16cc:2 via fe80::225:31ff:fe01:cc" so that the hosts on the Ethernet (2002:ad4c:16cc:1) will automatically pick up the route? The route works if I add it to the boxes manually. I've tried getting radvd on the plugbox to do this but I've had no success.

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Ubuntu Networking :: Subnet Unreachable Internet Is Reachable

Jul 28, 2011

I dont even know where to start looking on Google.Just in case this matters, for completeness.I've an inactive eth0 (wired ethernet link) with static IP.Other possibly relevant details:I'm using an old 802.11b card. Cant imagine this is relevant, because the internet is working fine as far as pinging anything outside the local network goes.

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Networking :: I.P Addressing For Simple Screened Subnet Architecture?

Jan 8, 2011

I'm wanting to set up a network that has a simple screened subnet architecture. The boarder router will have a switch plugged into it. My servers will be plugged into this switch. Also plugged into this switch will be a dedicated firewall. This firewall will protect the internal network. The boarder router is not very flexible. You can have hosts that use dhcp but that get the same internal I.P address each time their interface is configured.Or you can configure static I.Ps on hosts that are outside the dhcp range of the router, but that have the same subnet address.

The most simple way to set up such a network would be for every interface to have a static internal address that is obtained via dhcp from the boarder router. Like i said the boarder router is doesn't give you much freedom. Meaning that it lets you have a static internal address but not a different network address for different interfaces. That is where the confusion is, for me. If all the interfaces that get theirI.P addresses from the boarder router are on the same network, then what about the systems on the internal network. They might as well get their I.Ps from the boarder router as well, to avoid NAT being done twice before their packets get sent out to the Internet?.I wanted a three interface firewall to separate the DMZ from the internal network, instead of using a screened subnet architecture, but the boarder router only allowed one interface to be in the DMZ, i think and it didn't seem to have a well designed way of controlling the DMZ ie setting a new default gateway etc.

Should i let NAT be done twice for packets from the internal network i.e have the dedicated firewall do dhcp and NAT for the internal network, but this firewall's external interface have a static internal I.P from the boarder router, and the internal I.P of the dedicated firewall have a static internal I.P from the router as well?. It looks like all the interfaces have to have the same network and subnet address, except the machines on the internal network(which can get their I.P from the dedicated firewall)

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