[ovs-discuss] UDP datagram size effect at flow table hitting

[Justin Pettit]

> On Sep 11, 2019, at 7:04 AM, 병욱이 <nimdrak at gmail.com> wrote:
> 
> I did a small experiment with ONOS 3.0.5, OVS 2.0.2(OF 1.0), mininet 2.3.0d5
> 
> I found when making flow rule about L4 port, hitting flow table
> doesn't work properly.
> 
> For example, about UDP flow, ip_src=10.0.0.3, ip_dst=10.0.0.2, udp_dst=50000
> 
>       1)  cookie=0x4c0000ef7faa8a, duration=332.717s, table=0, n_packets=8974,
>        n_bytes=557090858, idle_age=153, priority=65050,ip,nw_dst=10.0.0.2
>        actions=output:4
> 
>        2) cookie=0x4c0000951b3b33, duration=332.636s, table=0, n_packets=10,
>        n_bytes=460,idle_age=168,priority=65111,udp,nw_src=10.0.0.3,nw_dst=10.0.0.2,
>        tp_dst=50000 actions=output:3
> 
> Although the flow rule 2 have higher priority and more match field,
> the flow rule 2 was hit.
> 
> When doing trouble shooting, I found the UDP datagram size affect the result.
> 
> For 63kBytes datagram, the flow rule 1 is hit.
> 
> However for 1500Bytes datagram, the flow rule 2 is hit.
> 
> I think the datagram size degrade the match of OVS but I don't know exactly

63KB is pretty big for a datagram.  Is it getting fragmented?  If so, only the first fragment contains the UDP information.

--Justin