strange routing

[Xian]

I have a friend who has set up a FreeBSD box (called Atlantis) as a router 
between his LAN and the Internet. It connects to the Internet and can make 
and receive connections ok (eg I can ssh in from outside, and he can ssh 
out), but other computers on the network can't connect out through it.
The strange thing is that when the default route on Atlantis is set to the old 
router he has and this is used to connect to the Internet, other computers on 
the network can connect out to the Internet. Trace route confirms the 
connection is going via Atlantis then the old router.
The IP address of Atlantis is 192.168.0.71 and the IP address of the old 
router is 192.168.101

Here are some bits a pices that might be usefull:

NOT VIA OLD ROUTER:
[ian at atlantis:~] %netstat -r -f inet
Routing tables

Internet:
Destination        Gateway            Flags    Refs      Use  Netif Expire
default            212.104.130.202    UGS         0      456   tun0
localhost          localhost          UH          0       11    lo0
192.168.0          link#1             UC          0        0   sis0
192.168.0.1        00:0c:6e:fa:17:cd  UHLW        0      845   sis0   1024
192.168.0.2        00:01:03:86:8d:3e  UHLW        0       28   sis0   1000
212.104.130.202    82.152.149.159     UH          1        8   tun0
[ian at atlantis:~] %ifconfig
sis0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=8<VLAN_MTU>
        inet 192.168.0.71 netmask 0xffffff00 broadcast 192.168.0.255
        inet6 fe80::2d0:9ff:fe85:c328%sis0 prefixlen 64 scopeid 0x1
        ether 00:d0:09:85:c3:28
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active
plip0: flags=108810<POINTOPOINT,SIMPLEX,MULTICAST> mtu 1500
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet 127.0.0.1 netmask 0xff000000
        inet6 ::1 prefixlen 128
        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
tun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1500
        inet 82.152.149.159 --> 212.104.130.202 netmask 0xffffffff
        Opened by PID 413
[ian at atlantis:~] %sysctl net.inet.ip.forwarding
net.inet.ip.forwarding: 1
[ian at atlantis:~] %uname -a
FreeBSD atlantis.pegasus 5.3-RELEASE-p2 FreeBSD 5.3-RELEASE-p2 #2: Tue Dec 21 
22:22:43 GMT 2004     root at atlantis.pegasus:/usr/obj/usr/src/sys/MYKERNEL  
i386


VIA OLD ROUTER:
[ian at atlantis:~] %netstat -r -f inet
Routing tables

Internet:
Destination        Gateway            Flags    Refs      Use  Netif Expire
default            192.168.0.101      UGS         0      436   sis0
localhost          localhost          UH          0        7    lo0
192.168.0          link#1             UC          0        0   sis0
192.168.0.1        00:0c:6e:fa:17:cd  UHLW        0      434   sis0    947
192.168.0.2        00:01:03:86:8d:3e  UHLW        0        3   sis0    903
192.168.0.101      00:e0:18:76:f7:7f  UHLW        1        0   sis0    984
[ian at atlantis:~] %ifconfig
sis0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        options=8<VLAN_MTU>
        inet 192.168.0.71 netmask 0xffffff00 broadcast 192.168.0.255
        inet6 fe80::2d0:9ff:fe85:c328%sis0 prefixlen 64 scopeid 0x1
        ether 00:d0:09:85:c3:28
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active
plip0: flags=108810<POINTOPOINT,SIMPLEX,MULTICAST> mtu 1500
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet 127.0.0.1 netmask 0xff000000
        inet6 ::1 prefixlen 128
        inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3
[ian at atlantis:~] %sysctl net.inet.ip.forwarding
net.inet.ip.forwarding: 1

A TRACEROUT FROM ANTHER MACHINE (when using old router):
C:\Documents and Settings\Paul>tracert www.bbc.co.uk

Tracing route to www.bbc.net.uk [212.58.224.121]
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms  192.168.0.71
  2     9 ms     1 ms     1 ms  192.168.0.101
  3    16 ms    15 ms    15 ms  212.104.130.202
  4    16 ms    18 ms    15 ms  81.5.191.113
  5    16 ms    16 ms    17 ms  ge1-1-core4.th.eclipse.net.uk [81.5.191.2]
  6    17 ms    16 ms    15 ms  212.58.238.209
  7    17 ms    15 ms    16 ms  212.58.238.153
  8    19 ms    19 ms    18 ms  www21.thdo.bbc.co.uk [212.58.224.121]

Trace complete.

A TRACEROUT FROM ANTHER MACHINE (not old router):
C:\Documents and Settings\Paul>tracert www.bbc.co.uk
Unable to resolve target system name www.bbc.co.uk.

C:\Documents and Settings\Paul>tracert 212.58.224.121

Tracing route to 212.58.224.121 over a maximum of 30 hops

  1    <1 ms    <1 ms    <1 ms  192.168.0.71
  2     *        *        *     Request timed out.
  3     *        *        *     Request timed out.
  4     *        *        *     Request timed out.
  5     *        *        *     Request timed out.
  6     *        *        *     Request timed out.
etc.....

Please CC to me as I am not subscribed t this list.
Thanks in advance for any ideas/help/kicks in the right direction.
-- 
/Xian

"Arguing with an engineer is like wrestling with a pig in mud.
After a while, you realise the pig is enjoying it."
Unknown Author