[dpdk-users] Weird phenomenon involving KNI

DoHyung Kim dohyung.kim at fluidic.io
Wed Jan 2 14:04:50 CET 2019

It's not relevant to DPDK at all. I was trying to put two NICs in a host to
single subnet, and even w/o DPDK involved, the NICs didn't work properly.
Googling turned out that one can't use multiple NICs in a Linux host in
single subnet under the default, out of the box, configuration.

I guess many of subscribers in this mailing list should already be familar
w/ the problem. But I describe how I've solved the problem below in the
hope that it may be helpful to someone like me:

If one wants such a network setup, one needs to tweak routing rules
together w/ a few changes to the way ARP is handled. An interesting point
here is one needs to set routing rules correctly in order to just get ARP
replies work as intenteded, though ARP replies are not strictly relevant to
the outgoing packets.

Please refer to the following doc: https://access.redhat.com/solutions/30564
In summary, each NIC needs to have a separate routing table and a routing
rule linking the table w/ the IP address of the NIC.
I added arp_ignore = 1 together w/ arp_announce = 2 since other docs on the
ARP flux problem suggests doing so.


2019년 1월 2일 (수) 오후 9:38, Jay Rolette <rolette at infinite.io>님이 작성:

> On Tue, Jan 1, 2019 at 4:05 AM DoHyung Kim <dohyung.kim at fluidic.io> wrote:
>> It was a consequence of the well-known behavior of Linux kernel regarding
>> ARP handling when multiple NICs are on the same subnet.
> What solution did you end up going with?

DoHyung Kim
Fluidic Inc.

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