[Bridge] Man-in-the-middle scenario within vmware - problem

[Bridge] Man-in-the-middle scenario within vmware - problem

[Patrick Nagel]

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Hi there,

I'm trying to set up a man-in-the-middle scenario within a VMWare Workstation 
team, using brctl. What I want is the following:

PC1 eth0 >---LAN-segment-1---< eth0 PCMITM eth1 >---LAN-segment-2---< eth0 PC2

Now I did the following on PCMITM (PC man in the middle):

ifconfig eth0 down
ifconfig eth1 down
brctl addbr lnxbr0
brctl addif lnxbr0 eth0
brctl addif lnxbr0 eth1
ifconfig eth0 0.0.0.0
ifconfig eth1 0.0.0.0
ifconfig lnxbr0 up

All commands exit successfully and I get eth0, eth1 and lnxbr0 listed in 
ifconfig.
brctl show says:

bridge name	bridge id		STP enabled	interfaces
lnxbr0		8000.000c296df055	no		eth1
							eth0

which also seems alright to me.

But now the problem: although PC1 and PC2 are in the same IP subnet (addresses 
192.168.222.1 and 192.168.222.2), a ping doesn't pass the bridge. By 
starting "ping pc2" on PC1 and "ping pc1" on PC2, I ensure that both machines 
are transmitting data frequently, and thus should show up in "brctl 
showmacs", but
brctl showmacs lnxbr0 says:

port no	mac addr		is local?	ageing timer
  1	00:0c:29:6d:f0:55	yes		   0.00
  2	00:0c:29:6d:f0:5f	yes		   0.00
  2	00:0c:29:97:e3:a6	no		   0.14

So there is one NIC missing - that one of PC1.

Does anyone have an explanation? I don't know what could be wrong in my setup, 
I don't even know where to start... Any help is appreciated.

By the way: The LAN segments within VMWare seem to be working. If I give each 
NIC on PCMITM an IP address (with no bridge on PCMITM), I can transfer data 
from PC1 to PCMITM (and vice versa) and from PC2 to PCMITM (and vice versa).

Patrick.

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Re: [Bridge] Man-in-the-middle scenario within vmware - problem

[Stephen Hemminger]

On Sun, 10 Dec 2006 19:09:27 +0100
Patrick Nagel <mail@patrick-nagel.net> wrote:

> Hi there,
> 
> I'm trying to set up a man-in-the-middle scenario within a VMWare Workstation 
> team, using brctl. What I want is the following:
> 
> PC1 eth0 >---LAN-segment-1---< eth0 PCMITM eth1 >---LAN-segment-2---< eth0 PC2
> 
> Now I did the following on PCMITM (PC man in the middle):
> 
> ifconfig eth0 down
> ifconfig eth1 down
> brctl addbr lnxbr0
> brctl addif lnxbr0 eth0
> brctl addif lnxbr0 eth1
> ifconfig eth0 0.0.0.0
> ifconfig eth1 0.0.0.0
> ifconfig lnxbr0 up
> 
> All commands exit successfully and I get eth0, eth1 and lnxbr0 listed in 
> ifconfig.
> brctl show says:
> 
> bridge name	bridge id		STP enabled	interfaces
> lnxbr0		8000.000c296df055	no		eth1
> 							eth0
> 
> which also seems alright to me.
> 
> But now the problem: although PC1 and PC2 are in the same IP subnet (addresses 
> 192.168.222.1 and 192.168.222.2), a ping doesn't pass the bridge. By 
> starting "ping pc2" on PC1 and "ping pc1" on PC2, I ensure that both machines 
> are transmitting data frequently, and thus should show up in "brctl 
> showmacs", but
> brctl showmacs lnxbr0 says:
> 
> port no	mac addr		is local?	ageing timer
>   1	00:0c:29:6d:f0:55	yes		   0.00
>   2	00:0c:29:6d:f0:5f	yes		   0.00
>   2	00:0c:29:97:e3:a6	no		   0.14
> 
> So there is one NIC missing - that one of PC1.
> 
> Does anyone have an explanation? I don't know what could be wrong in my setup, 
> I don't even know where to start... Any help is appreciated.
> 
> By the way: The LAN segments within VMWare seem to be working. If I give each 
> NIC on PCMITM an IP address (with no bridge on PCMITM), I can transfer data 
> from PC1 to PCMITM (and vice versa) and from PC2 to PCMITM (and vice versa).
> 
> Patrick.

Did you wait until after the "forwarding delay" expired (30 seconds) or set
turn forwarding delay off?

It may be that the ehternet driver doesn't support promiscious mode
and/or doesn't expect non-local source adresses. You need to see where packets
are being dropped, could be the ethernet driver, or switch with network access
control or inside the bridge.

Also check that the drivers correctly report carrier state.

brctl show lnxbr0

Should show both devices in forwarding atate.

Re: [Bridge] Man-in-the-middle scenario within vmware - problem

[Patrick Nagel]

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Hi Stephen,

thanks for answering!

> Did you wait until after the "forwarding delay" expired (30 seconds) or set
> turn forwarding delay off?
Yes to waiting.

> It may be that the ehternet driver doesn't support promiscious mode
> and/or doesn't expect non-local source adresses. You need to see where
> packets are being dropped, could be the ethernet driver, or switch with
> network access control or inside the bridge.
The driver seems to support promiscious mode, as I get the following from 
dmesg after setting up the bridge:

[17179785.256000] Bridge firewalling registered
[17179785.264000] device eth0 entered promiscuous mode
[17179785.264000] audit(1166040131.368:2): dev=eth0 prom=256 old_prom=0 
auid=4294967295
[17179785.268000] device eth1 entered promiscuous mode
[17179785.268000] audit(1166040131.372:3): dev=eth1 prom=256 old_prom=0 
auid=4294967295
[17179785.272000] eth0: link up
[17179785.280000] eth1: link up
[17179785.284000] lnxbr0: port 2(eth1) entering learning state
[17179785.284000] lnxbr0: port 1(eth0) entering learning state
[17179795.336000] eth1: no IPv6 routers present
[17179795.848000] eth0: no IPv6 routers present
[17179796.040000] lnxbr0: no IPv6 routers present
[17179800.284000] lnxbr0: topology change detected, propagating
[17179800.284000] lnxbr0: port 2(eth1) entering forwarding state
[17179800.284000] lnxbr0: topology change detected, propagating
[17179800.284000] lnxbr0: port 1(eth0) entering forwarding state

Look at those "screenshots":

After some "ping" packets from PC1 to PC2, the statistics look like this:

$ ifconfig eth0 && ifconfig eth1 && ifconfig lnxbr0
eth0      Link encap:Ethernet  HWaddr 00:0C:29:6D:F0:55
          inet6 addr: fe80::20c:29ff:fe6d:f055/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:48 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:2880 (2.8 KiB)  TX bytes:468 (468.0 b)
          Interrupt:177 Base address:0x1080

eth1      Link encap:Ethernet  HWaddr 00:0C:29:6D:F0:5F
          inet6 addr: fe80::20c:29ff:fe6d:f05f/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:54 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:3348 (3.2 KiB)
          Interrupt:185 Base address:0x1400

lnxbr0    Link encap:Ethernet  HWaddr 00:0C:29:6D:F0:55
          inet6 addr: fe80::20c:29ff:fe6d:f055/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:48 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:2208 (2.1 KiB)  TX bytes:468 (468.0 b)

So the packets come in on eth0, and they're sent out on eth1, but there is no 
answer received from PC2. BUT on PC2, ifconfig says that there were 57 
packets in and 57 packets out on eth0.

Now let's do it the other way round:

$ ifconfig eth0 && ifconfig eth1 && ifconfig lnxbr0
eth0      Link encap:Ethernet  HWaddr 00:0C:29:6D:F0:55  
          inet6 addr: fe80::20c:29ff:fe6d:f055/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:48 errors:0 dropped:0 overruns:0 frame:0
          TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2880 (2.8 KiB)  TX bytes:1548 (1.5 KiB)
          Interrupt:177 Base address:0x1080 

eth1      Link encap:Ethernet  HWaddr 00:0C:29:6D:F0:5F  
          inet6 addr: fe80::20c:29ff:fe6d:f05f/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:18 errors:0 dropped:0 overruns:0 frame:0
          TX packets:54 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:1080 (1.0 KiB)  TX bytes:3348 (3.2 KiB)
          Interrupt:185 Base address:0x1400 

lnxbr0    Link encap:Ethernet  HWaddr 00:0C:29:6D:F0:55  
          inet6 addr: fe80::20c:29ff:fe6d:f055/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:66 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:3036 (2.9 KiB)  TX bytes:468 (468.0 b)

And it's the same - the packets come in on eth1, go out on eth0, but the 
echoes never make it back through eth0.

So where exactly do they get stuck? I really don't know how to proceed...

> Also check that the drivers correctly report carrier state.
>
> brctl show lnxbr0
... is always like this:

bridge name	bridge id		STP enabled	interfaces
lnxbr0		8000.000c296df055	no		eth1
							eth0

> Should show both devices in forwarding atate.
Where could I see that?

Thanks for your help!

Patrick.

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