Hello,
What I do is have the linux box claim all of the public IPs as its own, and then use IPTABLES to DNAT/SNAT to/from private IPs as needed. You can dedicate a public IP to a specific private IP, so the computer on your network with that private IP appears to all of the world as if it actually has the public IP. This has the added advantage that if your public IPs change for some reason, you just need to update IPTABLEs and the computers on your network will only need slight (if any) tweaking.
That is basically what I am doing currently (with only one IP though obtained via cablemodem). However the person that makes all of this happen (SHDSL+ leased line) absolutely wants the public IP on his machine so I can't go that route.
The IPs however are unlikely to change in the foreseeable future, they are assigned and the person who makes this possible owns them as he is a (small) ISP. So changing should not occur.
In this setup, all of your public IPs are on one ethernet port, and all of your private IPs are on the other. If you desire, you can give one of the public IPs to the linux box itself (though for security reasons, I personally do not do this... in fact, the only traffic I let the linux box pass to the internet is forwarded packets... nothing originating from itself).
Well at least SSH for management is usually what I do. However I do run other things on the fw box. Most of it is bound to the lan if only, so I don't see any problem with it security wise.
This may be what you had in mind when you considered the option of a transparent bridge...
No I really meant a transparent bridge as in
brctl addbr br0 brctl addif br0 lan brctl addif br0 wan ifconfig lan 0.0.0.0 promisc up ifconfig wan 0.0.0.0 promisc up
And some netfilter lines to allow forwarding between the ifs on the allowed ports. This has the benefit that the filtering box is actually invisible (no route hop, no traceroute step) and can be taken down and the cables between lan and wan shortcutted without losing connectivity.
I still think that is the best thing for my case as I know the bridge stuff fairly well. The only issue holding me back is the fact that the (real) interfaces need to be in promiscous mode (not 100% sure, need to test) and the lan nic is a gigE card.
CU
René
----- Original Message ----- From: "Rene Gallati" <lartc@xxxxxxxxxxxxx> To: <LARTC@xxxxxxxxxxxxxxx> Sent: Sunday, October 31, 2004 9:55 AM Subject: Howto route through
Hello list,
I'm having a little trouble imagining a setup I'll soon have.
I am in the process of getting a routed /28 to my homeLAN. What I want to do is to put a linux box in front of the lan to filter some of the unneeded and potential dangerous ports. Now the box has 2 nics, one for the inside one for the outside.
How should I go on to setup those NICs when
a) the PCs in the net should have their official IP address from the /28 net
and
b) the filtering linux box should at the same time have one IP address from the same range for some services it provides
The dilemma I see (maybe it is none but I just don't know)
if I put it this way that I have the IP of the /28er range on one nic and nothing to put on the other ?
Example: Range is 1.2.3.0/28 (1.2.3.0 - 1.2.3.15)
eth0: 1.2.3.1 eth1: ??? ---- Internet ------- FW Box ------ LAN (1.2.3.0/28)
The FW box should be reachable by both the hosts in the LAN as well as from the internet using the assigned IP. Don't I run into troubles having an IP on one NIC which does belong to a net that is located on the side of another NIC ?
I know that the most specific entry (full IP) overrides or wins over the less specific ones (the net) but does this setup work so that the LAN clients can access the FW box just like every other host on the internet? How do I configure eth1 ? Just bring it up without any IP at all?
Or should I better make the FW box a transparent bridge for the filtering with one IP where it reacts itself ?
Thanks for all hints
CU
René _______________________________________________ LARTC mailing list / LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/
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