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* Query regarding ARP request on a multi-homed system
@ 2014-06-26  6:13 Chaitra Ramaiah
  2014-06-26  6:46 ` ankur dwivedi
  2014-06-26  7:38 ` wei zhang
  0 siblings, 2 replies; 6+ messages in thread
From: Chaitra Ramaiah @ 2014-06-26  6:13 UTC (permalink / raw)
  To: kernelnewbies

Hi,

  Have a doubt regarding ARP behavior in case of a multi-homed linux box.

  Assume there are two interfaces eth0 and eth1 each configured with
IPs belonging to differrent
  subnets. Say IP1 is assigned to eth0 and IP2 to eth1. Now if an ARP
request comes on eth0
  for IP2, what is the behavior on Linux?

  Thanks in advance for your answers.

Thanks,
Chaitra

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Query regarding ARP request on a multi-homed system
  2014-06-26  6:13 Query regarding ARP request on a multi-homed system Chaitra Ramaiah
@ 2014-06-26  6:46 ` ankur dwivedi
  2014-06-26  7:09   ` Sudip Mukherjee
  2014-06-26  7:38 ` wei zhang
  1 sibling, 1 reply; 6+ messages in thread
From: ankur dwivedi @ 2014-06-26  6:46 UTC (permalink / raw)
  To: kernelnewbies

In my guess the eth0 interface will not do anything and drop the packet.

On Thu, Jun 26, 2014 at 11:43 AM, Chaitra Ramaiah <linux.delve@gmail.com> wrote:
> Hi,
>
>   Have a doubt regarding ARP behavior in case of a multi-homed linux box.
>
>   Assume there are two interfaces eth0 and eth1 each configured with
> IPs belonging to differrent
>   subnets. Say IP1 is assigned to eth0 and IP2 to eth1. Now if an ARP
> request comes on eth0
>   for IP2, what is the behavior on Linux?
>
>   Thanks in advance for your answers.
>
> Thanks,
> Chaitra
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies



-- 
Thanks

Ankur Dwivedi

You can follow me on twitter @ankurdwi

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Query regarding ARP request on a multi-homed system
  2014-06-26  6:46 ` ankur dwivedi
@ 2014-06-26  7:09   ` Sudip Mukherjee
  0 siblings, 0 replies; 6+ messages in thread
From: Sudip Mukherjee @ 2014-06-26  7:09 UTC (permalink / raw)
  To: kernelnewbies

On Thu, Jun 26, 2014 at 12:16 PM, ankur dwivedi <ankurengg2003@gmail.com> wrote:
> In my guess the eth0 interface will not do anything and drop the packet.

I happen to be the admin of a few server also and one of them is
having multiple lan card. In that , one card is configured as
192.168.1.1 (eth1) and the another 192.168.2.1 (eth2) and the other
(eth0) for global ip address .
Now , i just tried this - from 192.168.1.1 network (from the lan of
eth1)  , i tried to ping 192.168.2.1 and I received the reply . So the
interface is not dropping the packet .

>
> On Thu, Jun 26, 2014 at 11:43 AM, Chaitra Ramaiah <linux.delve@gmail.com> wrote:
>> Hi,
>>
>>   Have a doubt regarding ARP behavior in case of a multi-homed linux box.
>>
>>   Assume there are two interfaces eth0 and eth1 each configured with
>> IPs belonging to differrent
>>   subnets. Say IP1 is assigned to eth0 and IP2 to eth1. Now if an ARP
>> request comes on eth0
>>   for IP2, what is the behavior on Linux?
>>
>>   Thanks in advance for your answers.
>>
>> Thanks,
>> Chaitra
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
>
> --
> Thanks
>
> Ankur Dwivedi
>
> You can follow me on twitter @ankurdwi
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

^ permalink raw reply	[flat|nested] 6+ messages in thread
* Query regarding ARP request on a multi-homed system
  2014-06-26  6:13 Query regarding ARP request on a multi-homed system Chaitra Ramaiah
  2014-06-26  6:46 ` ankur dwivedi
@ 2014-06-26  7:38 ` wei zhang
  2014-06-26 17:58   ` Dave Tian
  1 sibling, 1 reply; 6+ messages in thread
From: wei zhang @ 2014-06-26  7:38 UTC (permalink / raw)
  To: kernelnewbies


At 2014-06-26 02:13:30, "Chaitra Ramaiah" <linux.delve@gmail.com> wrote:
>Hi,
>
>  Have a doubt regarding ARP behavior in case of a multi-homed linux box.
>
>  Assume there are two interfaces eth0 and eth1 each configured with
>IPs belonging to differrent
>  subnets. Say IP1 is assigned to eth0 and IP2 to eth1. Now if an ARP
>request comes on eth0

>  for IP2, what is the behavior on Linux?


I'm not familiar with networking, but arp_announce and arp_ignore in 
Documentation/networking/ip-sysctl.txt maybe the answer!


>
>  Thanks in advance for your answers.
>
>Thanks,
>Chaitra
>
>_______________________________________________
>Kernelnewbies mailing list
>Kernelnewbies at kernelnewbies.org
>http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
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^ permalink raw reply	[flat|nested] 6+ messages in thread
* Query regarding ARP request on a multi-homed system
  2014-06-26  7:38 ` wei zhang
@ 2014-06-26 17:58   ` Dave Tian
  2014-06-27  4:44     ` Chaitra Ramaiah
  0 siblings, 1 reply; 6+ messages in thread
From: Dave Tian @ 2014-06-26 17:58 UTC (permalink / raw)
  To: kernelnewbies

arp_filter may fit better.

	0 - (default) The kernel can respond to arp requests with addresses
	from other interfaces. This may seem wrong but it usually makes
	sense, because it increases the chance of successful communication.
	IP addresses are owned by the complete host on Linux, not by
	particular interfaces. Only for more complex setups like load-
	balancing, does this behaviour cause problems.

-daveti



On Jun 26, 2014, at 12:38 AM, wei zhang <asuka.com@163.com> wrote:

> 
> At 2014-06-26 02:13:30, "Chaitra Ramaiah" <linux.delve@gmail.com> wrote:
> >Hi,
> >
> >  Have a doubt regarding ARP behavior in case of a multi-homed linux box.
> >
> >  Assume there are two interfaces eth0 and eth1 each configured with
> >IPs belonging to differrent
> >  subnets. Say IP1 is assigned to eth0 and IP2 to eth1. Now if an ARP
> >request comes on eth0
> >  for IP2, what is the behavior on Linux?
> 
> I'm not familiar with networking, but arp_announce and arp_ignore in 
> Documentation/networking/ip-sysctl.txt maybe the answer!
> 
> >
> >  Thanks in advance for your answers.
> >
> >Thanks,
> >Chaitra
> >
> >_______________________________________________
> >Kernelnewbies mailing list
> >Kernelnewbies at kernelnewbies.org
> >http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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^ permalink raw reply	[flat|nested] 6+ messages in thread
* Query regarding ARP request on a multi-homed system
  2014-06-26 17:58   ` Dave Tian
@ 2014-06-27  4:44     ` Chaitra Ramaiah
  0 siblings, 0 replies; 6+ messages in thread
From: Chaitra Ramaiah @ 2014-06-27  4:44 UTC (permalink / raw)
  To: kernelnewbies

Thanks guys for your reponses. It helped.

Taking a cue from your responses, did a bit of digging from resources
and this is what it all boils down to:
1) arp_filter works well if the IPs on the interfaces belong to
differrent subnets.
2) If the IPs share the same subnet, then arp_announce and arp_ignore
does the job. Specifically arp_ignore takes 1 and arp_ignore should
take 2 for this situation.

Thanks all.

Regards,
Chaitra


On Thu, Jun 26, 2014 at 11:28 PM, Dave Tian <dave.jing.tian@gmail.com> wrote:
> arp_filter may fit better.
>
> 	0 - (default) The kernel can respond to arp requests with addresses
> 	from other interfaces. This may seem wrong but it usually makes
> 	sense, because it increases the chance of successful communication.
> 	IP addresses are owned by the complete host on Linux, not by
> 	particular interfaces. Only for more complex setups like load-
> 	balancing, does this behaviour cause problems.
>
>
> -daveti
>
>
>
> On Jun 26, 2014, at 12:38 AM, wei zhang <asuka.com@163.com> wrote:
>
>
> At 2014-06-26 02:13:30, "Chaitra Ramaiah" <linux.delve@gmail.com> wrote:
>>Hi,
>>
>>  Have a doubt regarding ARP behavior in case of a multi-homed linux box.
>>
>>  Assume there are two interfaces eth0 and eth1 each configured with
>>IPs belonging to differrent
>>  subnets. Say IP1 is assigned to eth0 and IP2 to eth1. Now if an ARP
>>request comes on eth0
>>  for IP2, what is the behavior on Linux?
>
> I'm not familiar with networking, but arp_announce and arp_ignore in
> Documentation/networking/ip-sysctl.txt maybe the answer!
>
>>
>>  Thanks in advance for your answers.
>>
>>Thanks,
>>Chaitra
>>
>>_______________________________________________
>>Kernelnewbies mailing list
>>Kernelnewbies at kernelnewbies.org
>>http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2014-06-27  4:44 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-06-26  6:13 Query regarding ARP request on a multi-homed system Chaitra Ramaiah
2014-06-26  6:46 ` ankur dwivedi
2014-06-26  7:09   ` Sudip Mukherjee
2014-06-26  7:38 ` wei zhang
2014-06-26 17:58   ` Dave Tian
2014-06-27  4:44     ` Chaitra Ramaiah

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