[ovs-discuss] udp checksum issue with openvswitch

Jesse Gross jesse at nicira.com
Sat Aug 24 18:54:10 UTC 2013


On Sat, Aug 24, 2013 at 8:15 AM, Rakesh B.K <bk.rakesh at ymail.com> wrote:
> Hello,
>
> Here is another addition to my previous comment.
>
> I had a walk-through on some parts of openVSwitch datapath code. Here is my
> analysis on why the checksum is being set to 0x0000 instead of 0xFFFF:
>     1. when the flow look-up table entry does not match with the key(when
> the function ovs_flow_tbl_lookup() returns false).
>     2. During no flow entry, a new netlink message will be created and the
> packet received from vnetX(guest interface netdev_port) is copied
>        using the function skb_copy_and_csum_dev(). After this, the
> skb->ip_summed bit field is set to CHECKSUM_NONE.
>
> For the checksum to be correct, the flow table lookup returns true and
> forwards the packet from vnetX(Guest interfce netdev_port) to ethX(Host)
> interface.
>
> Please let me know if my observations are correct.

Yes, that's right.



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