Masquerade difficulties

Masquerade difficulties

[Andrew Beekhof]

Hi All,

I'm having some difficulties getting masquerading to work and hoping
for some pointers...

The server (BoxA) has an ipsec (openswan) connection to another
network and I've run:
        echo 1 > /proc/sys/net/ipv4/ip_forward
        iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

On the client (BoxB) I've set the gateway for the other network to be BoxA.

Normally that does the trick, but not today...
If BoxB tries to ping BoxC, I can see BoxA forwarding the request but
it never gets an answer to forward back to BoxB.  Obviously BoxA can
ping BoxC directly.

There are no errors in dmesg or /var/log/messages and I tried
comparing "-j LOG" entries from my old server (a SLES9 box) where
masquerading works with those from my new server and everything looks
the same... it just doesn't work :(

Any pointers on what I'm missing or things to try would be appreciated.

Andrew

Distro: Gentoo
Kernel: 2.6.9-gentoo-r13
iptables: iptables v1.2.11
Openswan: Linux Openswan U2.2.0/K2.6.9-gentoo-r13 (native)

Re: Masquerade difficulties

[Trevor Cordes]

> I'm having some difficulties getting masquerading to work and hoping
> for some pointers...

I can try to help.  But you'll need to better describe your network 
layout.  Can you draw a little diagram showing where A, B & C are?

Are you sure that BoxC doesn't have some firewall on (XP SP2) that is 
eating the ping packets?

Re: Masquerade difficulties

[Andrew Beekhof]

On Fri, 7 Jan 2005 16:12:38 -0600, Trevor Cordes <trevor@tecnopolis.ca> wrote:
> > I'm having some difficulties getting masquerading to work and hoping
> > for some pointers...
> 
> I can try to help.  But you'll need to better describe your network
> layout.  Can you draw a little diagram showing where A, B & C are?

Sure, A & B are connected directly to a netgear DSL modem/hub.  C is
part of my company's network which I'm accessing over the internet
with ipsec.  I've also tried replacing C with google.com (after
specifying an appropriate routing rule) with no success.

Does that clear things up?

> 
> Are you sure that BoxC doesn't have some firewall on (XP SP2) that is
> eating the ping packets?

XP? God no!  All the machines are linux boxes running either SLES9 or
Gentoo :)  No firewall on B or C.

From what I can tell, the packets from BoxB are getting lost on BoxA. 
I just tried using telnet and tcpdump and although I get logs like
this:

Jan  8 08:35:55 BoxA IN=eth0 OUT=eth0 SRC=192.168.9.22 DST=10.10.2.86
LEN=60 TOS=0x10 PREC=0x00 TTL=63 ID=48952 DF PROTO=TCP SPT=34452
DPT=69 WINDOW=3840 RES=0x00 SYN URGP=0

... the packets never actually arrive at BoxC (10.10.2.86).  I dont
think they ever leave BoxA but I'm not sure I understand the tcpdump
output enough to say for sure.

A dump of my iptables in case it helps...

mayo linux # iptables -L -t nat
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
LOG        all  --  anywhere             anywhere            LOG level warning 
MASQUERADE  all  --  anywhere             anywhere            

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

mayo linux # iptables -L -t filter
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

mayo linux # iptables -L -t mangle
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
LOG        all  --  anywhere             anywhere            LOG level debug 

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination

Re: Masquerade difficulties

[Andrew Beekhof]

Looks like there is something going awry when 2.6, ipsec/openswan and
iptables are combined.

With further tinkering I was able to get ipsec working and
masquerading working separately, however masquerading through ipsec
still wouldnt work.  Just to be clear, I used www.google.com instead
of BoxC in the tests for which masquerading worked.

Anyway, I've reverted to a 2.4 kernel now and everything seems to be
working nicely.

I dont mind running some tests with my 2.6 setup if anyone is
interested though...

Andrew

On Sat, 8 Jan 2005 11:03:22 +0100, Andrew Beekhof <beekhof@gmail.com> wrote:
> On Fri, 7 Jan 2005 16:12:38 -0600, Trevor Cordes <trevor@tecnopolis.ca> wrote:
> > > I'm having some difficulties getting masquerading to work and hoping
> > > for some pointers...
> >
> > I can try to help.  But you'll need to better describe your network
> > layout.  Can you draw a little diagram showing where A, B & C are?
> 
> Sure, A & B are connected directly to a netgear DSL modem/hub.  C is
> part of my company's network which I'm accessing over the internet
> with ipsec.  I've also tried replacing C with google.com (after
> specifying an appropriate routing rule) with no success.
> 
> Does that clear things up?
> 
> >
> > Are you sure that BoxC doesn't have some firewall on (XP SP2) that is
> > eating the ping packets?
> 
> XP? God no!  All the machines are linux boxes running either SLES9 or
> Gentoo :)  No firewall on B or C.
> 
> From what I can tell, the packets from BoxB are getting lost on BoxA.
> I just tried using telnet and tcpdump and although I get logs like
> this:
> 
> Jan  8 08:35:55 BoxA IN=eth0 OUT=eth0 SRC=192.168.9.22 DST=10.10.2.86
> LEN=60 TOS=0x10 PREC=0x00 TTL=63 ID=48952 DF PROTO=TCP SPT=34452
> DPT=69 WINDOW=3840 RES=0x00 SYN URGP=0
> 
> ... the packets never actually arrive at BoxC (10.10.2.86).  I dont
> think they ever leave BoxA but I'm not sure I understand the tcpdump
> output enough to say for sure.
> 
> A dump of my iptables in case it helps...
> 
> mayo linux # iptables -L -t nat
> Chain PREROUTING (policy ACCEPT)
> target     prot opt source               destination
> 
> Chain POSTROUTING (policy ACCEPT)
> target     prot opt source               destination
> LOG        all  --  anywhere             anywhere            LOG level warning
> MASQUERADE  all  --  anywhere             anywhere
> 
> Chain OUTPUT (policy ACCEPT)
> target     prot opt source               destination
> 
> mayo linux # iptables -L -t filter
> Chain INPUT (policy ACCEPT)
> target     prot opt source               destination
> 
> Chain FORWARD (policy ACCEPT)
> target     prot opt source               destination
> 
> Chain OUTPUT (policy ACCEPT)
> target     prot opt source               destination
> 
> mayo linux # iptables -L -t mangle
> Chain PREROUTING (policy ACCEPT)
> target     prot opt source               destination
> 
> Chain INPUT (policy ACCEPT)
> target     prot opt source               destination
> 
> Chain FORWARD (policy ACCEPT)
> target     prot opt source               destination
> LOG        all  --  anywhere             anywhere            LOG level debug
> 
> Chain OUTPUT (policy ACCEPT)
> target     prot opt source               destination
> 
> Chain POSTROUTING (policy ACCEPT)
> target     prot opt source               destination
>