Thanks for the help Martin. I was under the impression that DNAT altered the packets on the PREROUTING chain going both ways. :What did you pour all over the documentation on the Internet? ;) Did it :get in your pores? I actually studied it so intently that I was sweating. :) :And one other thing! Make sure you have turned off reverse path :filtering This wasn't on, though I am not exactly sure what it does. Needless to say, everything is working well now. Thanks again. -Bryan -----Original Message----- From: Martin A. Brown [mailto:mabrown-lartc@xxxxxxxxxxxxxx] Sent: Wednesday, March 26, 2003 8:56 PM To: Bryan Goodgion Cc: lartc@xxxxxxxxxxxxxxx; Dave Salvador Subject: Re: [LARTC] Simple Mulitple Link Scenario Hi Bryan, [ please post any follow up messages in plain text. HTML messages don't archive well, contain lots of strangely escaped characters, and.... well, you probably know all of this...so keep it in plain text! ] I presume you have a single service on your internal network ("Linux Server") you wish to publish. It's not clear to me as I read your description exactly what the IP addressing of the various machines is. : I am trying to set up a network that can accept tcp connections over : two different isp connection. And, I trust you have read the following? http://linux-ip.net/html/adv-multi-internet.html#adv-multi-internet-inbo und http://lists.netfilter.org/pipermail/netfilter/2001-May/011697.html : The ultimate goal is to facilitate the : migration from one ISP to another ISP. I decided to delve into the : world of Linux Advanced Routing, so I poured over all of the : documentation on the internet. What did you pour all over the documentation on the Internet? ;) Did it get in your pores? : I have it set up in what I believe to be the case where it should : work, but I can't understand why it doesn't. Here is the drawing: <diagram snipped> : Here is what I have going. The router has a single interface that I : have given an IP address on the network space assigned by each ISP. : It is performing NAT using two DNAT iptables rules for the Linux Server : that is sitting behind it. The linux router takes $WAN1_IP -> : 10.0.2.205 and takes $WAN2_IP -> 10.0.2.206. I then set up a second : routing table so that I can have two default gateways depending on : which IP I want to take out. Here are the exact commands I have : issued: OK....that's what you should be doing, but that's not what you appear to be doing here: : iptables -t nat -A PREROUTING -j DNAT -dst $WAN1_IP to 10.0.2.205 : iptables -t nat -A PREROUTING -j DNAT -dst $WAN2_IP to 10.0.2.205 Here, the target IP is the same....10.0.2.205, for both links. Try this instead: iptables -t nat -A PREROUTING -j DNAT -dst $WAN2_IP to 10.0.2.206 (keep reading...) : ip route show table main | grep -Ev ^default \ : > | while read ROUTE ; do : > ip route add table 4 $ROUTE : > done : : ip route add default via $FIREWALL2_IP : ip route add default via $FIREWALL1_IP table 4 Yep! And everything should look dandy in table 4: # ip route show table 4 : ip rule add from $WAN1_SUBNET table 4 Now, you'll also want to add an entry to make sure that the packets associated with connections to 10.0.2.205 go via table 4: # ip rule add from 10.0.2.205 table 4 : After completing this setup, I am able to traceroute -s $WAN1_IP and : see it go out the WAN1 side and traceroute -s $WAN2_IP and see it go : out WAN2. These are locally generated packets, and the "ip rule add from $WAN1_SUBNET" will ensure you get the correct route. : I am also able to use the ip route get command and everything works as : I expect it to work. My first failure occurred when I tried to create : a tcp connection from the internet. It works coming in on $WAN2_IP and : fails using $WAN1_IP. This confirms my diagnosis. : The problem is that when I watch a dump of the outgoing packets while : trying to bring up a tcp connection to $WAN1_IP, I see the packets : coming in and then I see the reply going out to the MAC address of : $FIREWALL2 instead of the MAC address of $FIREWALL1 as it should and : thus the connection fails. Any ideas? Thanks in advance. And one other thing! Make sure you have turned off reverse path filtering: # echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter and the other interfaces. Good luck, -Martin -- Martin A. Brown --- SecurePipe, Inc. --- mabrown@xxxxxxxxxxxxxx
