On 5/9/25 6:19 AM, Thenveer Poolakkanni via discuss wrote:
> Hi Team,
>
> I’m currently working with Open vSwitch (OVS) using the DPDK datapath
> on a Alveo U200, and I’ve encountered an issue where packets are not
> being received back on the traffic generator after being transmitted
> by OVS.
>
> Setup Details:
>
> - Traffic Generator:
> - Port 0 → Connected to Alveo U200 pf0
> - Port 1 → Connected to Alveo U200 pf1
> - OVS is running on the Alveo U200 (datapath_type=netdev), and both
> `pf0` and `pf1` are added as DPDK ports to a bridge named `br0`.
>
> OVS Configuration:
> d76b4ea2-df9e-4d2e-8f9d-06210013ffef
> Bridge br0
> datapath_type: netdev
> Port br0
> Interface br0
> type: internal
> Port pf0
> Interface pf0
> type: dpdk
> options: {dpdk-devargs="0000:08:00.0", n_rxq="4",
> n_rxq_desc="1024", n_txq="4", n_txq_desc="1024"}
> Port pf1
> Interface pf1
> type: dpdk
> options: {dpdk-devargs="0000:08:00.1", n_rxq="4",
> n_rxq_desc="1024", n_txq="4", n_txq_desc="1024"}
>
> After sending packets from the traffic generator to `pf0`, here are the stats:
>
> OFPST_PORT reply (xid=0x2): 3 ports
> port LOCAL: rx pkts=0, bytes=0, drop=0, errs=0, frame=0, over=0, crc=0
> tx pkts=0, bytes=0, drop=100, errs=0, coll=0
> port pf0: rx pkts=100, bytes=6000, drop=0, errs=0, frame=?, over=?, crc=?
> tx pkts=0, bytes=0, drop=0, errs=0, coll=?
> port pf1: rx pkts=0, bytes=0, drop=0, errs=0, frame=?, over=?, crc=?
> tx pkts=100, bytes=6000, drop=0, errs=0, coll=?
>
>
> Why are packets being dropped at the `LOCAL` port, and is that affecting
> forwarding?
You're likely sending traffic only in one direction, so the bridge
can't learn where the destination is and broadcasts these packets
to every port on the bridge. The bridge port is probably down, so
packets sent to it a dropped. Broadcasting to kernel interfaces
will significantly affect performance, but your packets should still
arrive just fine on the other port. So, if you don't see them,
the problem is likely with the driver or a card or otherwise outside
of OVS.
To avoid brodcasting you either need to send some traffic in the
opposite direction or stop using the default NORMAL action in your
OpenFlow configuration. A rule like in_port=pf0,actions:pf1 would
just forward everything directly without learning and broadcasting.
Best regards, Ilya Maximets.
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