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Hi all
had an interresting problem the other day, just
thought i'd share it with you all and see if
any body else had a similar experience.
I set up a small nat/firewall box for a client of
ours. we had 5 interfaces and they were as follows
eth0 192.168.10.1 netmask
255.255.255.255 pointopoint 192.168.10.2 <--- adsl modem
doing nat
eth1 192.168.0.1 netmask
255.255.255.0
eth2 192.168.1.1 netmask
255.255.255.0
eth3 192.168.2.1 netmask
255.255.255.0
eth4 192.168.3.1 netmask
255.255.255.255 pointopoint 192.168.3.2 <-- some upstairs router
and the routing table looked like you would expect
it to, with
route add default gw 192.168.10.1 dev eth0
also we had
echo "1" > /proc/sys/net/ipv4/ip_forward
for simplicity , iptables rules were as follows
iptables -t nat --append POSTROUTING -o eth0 --jump
MASQUERADE
so, now all traffic using 192.168.0.1 , 1.1, 2.1
and 3.1 as a gateway should be able to reach the
internet via the modem on 192.168.10.2 , right ?
well, all icmp worked, perfectly
but everything else , ie , udp, tcp didn't
say for example http : packets get sent to tcp 80,
tcp replies get recieved, but no data gets back to
the user on 192.168.whatever
strange huh ?
so i thought my mtu was befuqed, so i do
iptables --append FORWARD --proto tcp --tcp-flags
SYN,RST SYN --jump TCPMSS --clamp-mss-to-pmtu
no luck though.
tried a plethora of other stuff too , but didn't
work, so i'll leave that there
obviously the nat works, becuase all my icmp's are
natted.
mmm
so i go into the boxes bios set up and tell it to
assign irq's to all pci devices automatically
boot up into linux and do
ifconfig eth4 up
eth4: error fetching interface information: Device
not found
eh ? wtf ? so i do
ifconfig eth0 up
and the device gets brought up
then i do ifconfig eth4 up
and it brings it up . Strange huh ?
so now i see that all my cards are swopped arround.
that which used to be eth0 is now eth4 and so
on and so on.
anyway, plug in the appropiate network cables to
the relevant nics and run the script
to a ping to google.com ... everything works fine.
right, so far so good. right back were i
started
now, do a HTTP-GET http://www.google.com and guess what
i get a lovely html page.
strange that changing the device irg assignment in
the bios solved my problem ?
any ideas what could have caused this ?
thanks a lot for bearing with my idiotic ramblings
so far
----------------
tanuki
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