IP Connection to own IP-Address goes over the network

IP Connection to own IP-Address goes over the network

Post by Roman Vytesn » Thu, 19 Dec 2002 20:02:32



Hi,

we have seen, that our application which sometimes connects to a
service on the same AIX Box it runs also uses the network (Destination
MAC Address is the router/gateway address, this box sends the packet
back to our AIX system).
On i.g. Windows NT if you send packets to your own IP-Adress the
kernel checks this out and does not send the packet over the cable.

Is there a way to configure the system not to send over the network?
(I have looked for any "no" params, but haven`t found something for my
problem)
We are using AIX 4.3.3-10

Greetings,
Roman

 
 
 

IP Connection to own IP-Address goes over the network

Post by Jason Mathe » Fri, 20 Dec 2002 02:41:00




>>Hi,

>>we have seen, that our application which sometimes connects to a
>>service on the same AIX Box it runs also uses the network (Destination
>>MAC Address is the router/gateway address, this box sends the packet
>>back to our AIX system).

>>On i.g. Windows NT if you send packets to your own IP-Adress the
>>kernel checks this out and does not send the packet over the cable.

>>Is there a way to configure the system not to send over the network?
>>(I have looked for any "no" params, but haven`t found something for my
>>problem)

> The truth is probably that you're either mistaken in your interpretation
> of the behavior you're seeing or the machine is not configured correctly.

> The behavior you describe existed long before it was implemented on
> Windows NT.  I've *never* heard of an operating system with an IP
> stack that doesn't behave this way.  The default behavior on AIX,
> as with all other UNIX systems I know of, is to put packets destined
> for a local interface in the IP input queue instead of passing it
> to the NIC.

> This behavior is so commonplace and longstanding that I would be
> very surprised if this were a bug in AIX.

> So what do your routing and interface tables look like?

> Regards,

> Nicholas

I always thought the resolver took care of that, so I just tried
it with tcpdump.  Sure enough, no packets on the net when you ping
yourself, either by name or IP.

-- Jason

 
 
 

IP Connection to own IP-Address goes over the network

Post by Nicholas Drone » Fri, 20 Dec 2002 06:28:01





>>>Is there a way to configure the system not to send over the network?
>>>(I have looked for any "no" params, but haven`t found something for my
>>>problem)
>> The truth is probably that you're either mistaken in your interpretation
>> of the behavior you're seeing or the machine is not configured correctly.
>> The behavior you describe existed long before it was implemented on
>> Windows NT.  I've *never* heard of an operating system with an IP
>> stack that doesn't behave this way.  The default behavior on AIX,
>> as with all other UNIX systems I know of, is to put packets destined
>> for a local interface in the IP input queue instead of passing it
>> to the NIC.

>> This behavior is so commonplace and longstanding that I would be
>> very surprised if this were a bug in AIX.
> I always thought the resolver took care of that, so I just tried
> it with tcpdump.  Sure enough, no packets on the net when you ping
> yourself, either by name or IP.

It's always been part of the kernel.

Regards,

Nicholas

--
Please do not reply to USENET posts, at least to mine, by email.

 
 
 

IP Connection to own IP-Address goes over the network

Post by Roman Vytesni » Fri, 20 Dec 2002 22:25:24


Hi again,

first thank you for your answers - but I still have the problem to see
packets for my own IP-Address on the network.
We used an ethernet-lan sniffer to filter the packets and we can see packets
from 10.1.2.13 to 10.1.2.13 on the cable.
Maybe I should give some more details:
We are running a database application which can serve clients directly
(informix net client) or via a second service (tcpip port 9500) on the aix
machine which connects to the local database and reformats the output for
the clients (the rdbms system is informix).
So if there is a request from a client for the port 9500 service there will
be generated a database request to the local machine and this one goes over
the network!?!?!
The second strange behavior is that the network packet has the MAC Address
from the router as destination MAC.

Maybe also interesting - we are running HACMP on this system - means the box
is part of a cluster. The second machine in the cluster has the same
problem.

Greetings,
Roman

 
 
 

IP Connection to own IP-Address goes over the network

Post by Jason Mathe » Sat, 21 Dec 2002 00:54:32



> Hi again,

> first thank you for your answers - but I still have the problem to see
> packets for my own IP-Address on the network.
> We used an ethernet-lan sniffer to filter the packets and we can see packets
> from 10.1.2.13 to 10.1.2.13 on the cable.
> Maybe I should give some more details:
> We are running a database application which can serve clients directly
> (informix net client) or via a second service (tcpip port 9500) on the aix
> machine which connects to the local database and reformats the output for
> the clients (the rdbms system is informix).
> So if there is a request from a client for the port 9500 service there will
> be generated a database request to the local machine and this one goes over
> the network!?!?!
> The second strange behavior is that the network packet has the MAC Address
> from the router as destination MAC.

> Maybe also interesting - we are running HACMP on this system - means the box
> is part of a cluster. The second machine in the cluster has the same
> problem.

> Greetings,
> Roman

Of course you have made sure that the other machine does not have the same IP address?

-- Jason

 
 
 

IP Connection to own IP-Address goes over the network

Post by Rick Jone » Sat, 21 Dec 2002 05:08:25



> The second strange behavior is that the network packet has the MAC
> Address from the router as destination MAC.

What does your routing table look like? Some stacks will automagically
create a host route for each of the local IP's that points at
127.0.0.1. On such stacks that causes local traffic to go to the
loopback interface rather than to the driver for the NIC's
involved. Generally the drivers would not put self-addressed frames
onto the network - they would loop them back internally. That you see
the router's MAC as the destination MAC would explain why the packet
upon getting to the driver would then go-out the wire.

You might examine your ARP tables then and perhaps clear the entry for
your own IPs. Perhaps the router is doing proxy ARP and your ARP code
got a bit confused? It is a stretch though.

Or perhaps it does have something to do with HACMP.

rick jones
--
denial, anger, bargaining, depression, acceptance, rebirth...
where do you want to be today?
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to raj in cup.hp.com  but NOT BOTH...

 
 
 

1. Send IP traffic to own IP address over first router/gateway

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How is it possible to patch the kernel or modify the routing tables
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Thanks.

Best wishes.

Achim

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