ipfw FWD, NAT and routing

[Gorm J. Siiger]

Hi

I'm experimenting with a dual ISP setup using NAT, as eacy ISP has provided
me with a subnet of official IP adresses.

Network setup:

--------	--------
| ISP1 |	| ISP2 |
--------	--------
   |               |
   |    --------   |
   -----|  FW  |----
        --------
           | 
           |
        --------
	|Server|
	--------

ISP1 LAN   : 20.0.0.0/29
ISP2 LAN   : 21.0.0.0/29
Server LAN : 10.0.0.0/24
Server IP on ISP1: 20.0.0.2
Server IP on LAN: 10.0.0.2
Server IP on ISP2: 21.0.0.2
Server IP on LAN: 10.0.0.3

The default gateway for the FW box is ISP1

I can connect to the whole world via ISP1 from the server with source IP
10.0.0.2 but when I try to connect to a host via ISP2 from source 10.0.0.3
the TCP connection is very slow, and there is a lot of retransmissions.

If I change the FW's default gateway to ISP2 it works like a charm.

Any suggestions on how to fix this problem.


/usr/local/etc/natd.conf
 use_sockets
 unregistered_only yes
 alias_address 20.0.0.6
 redirect_address 10.0.0.2 20.0.0.2
 redirect_address 10.0.0.3 21.0.0.2

/etc/rc.firewall
 ${fwcmd} add 400 divert natd all from any to any via ${isp0if}
 ${fwcmd} add 405 divert natd all from any to any via ${isp1if}
 ${fwcmd} add 505 fwd 21.0.0.0 ip from 21.0.0.0/29 to any


-- 
Gorm J. Siiger - SonnIT