Hi,
performing some tests, I noticed that on ixgbe when receiving UDP
packets with zero checksum (no checksum) over IPv4, the corresponding
ol_flag for the l4 checksum is set to PKT_RX_L4_CKSUM_BAD.
In particular, this apparently has an impact on OvS using ct() action
where UDP packets with zero checksum are not tracked because of that.
I also verified it using testpmd (on 20.11 and using the latest sources):
# lshw -businfo -c network
Bus info Device Class Description
=======================================================
pci@0000:01:00.0 em1 network 82599ES 10-Gigabit SFI/SFP+ Network
Connection
pci@0000:01:00.1 em2 network 82599ES 10-Gigabit SFI/SFP+ Network
Connection
testpmd -l 2,4 -w 0000:01:00.0 -- -i --port-topology=chained --enable-rx-cksum
testpmd> show device info all
********************* Infos for device 0000:01:00.0 *********************
Bus name: pci
Driver name: net_ixgbe
Devargs:
Connect to socket: 0
Port id: 0
MAC address: EC:F4:BB:DB:FC:18
Device name: 0000:01:00.0
Device speed capability: 1 Gbps 10 Gbps
testpmd> set fwd rxonly
testpmd> set verbose 1
testpmd> start
and sending packets from a tester machine using scapy (w/ non zero and zero
checksum):
sendp(Ether(src="ec:f4:bb:dc:09:d0",dst="ec:f4:bb:db:fc:18")/IP(src="192.168.30.200",
dst="192.168.30.100")/UDP()/Raw("a"*100), iface="em1")
sendp(Ether(src="ec:f4:bb:dc:09:d0",dst="ec:f4:bb:db:fc:18")/IP(src="192.168.30.200",
dst="192.168.30.100")/UDP(chksum=0)/Raw("a"*100), iface="em1")
the results are respectively:
port 0/queue 0: received 1 packets
src=EC:F4:BB:DC:09:D0 - dst=EC:F4:BB:DB:FC:18 - type=0x0800 - length=142 -
nb_segs=1 - hw ptype: L2_ETHER L3_IPV4 L4_UDP - sw ptype: L2_ETHER L3_IPV4
L4_UDP - l2_len=14 - l3_len=20 - l4_len=8 - Receive queue=0x0
ol_flags: PKT_RX_L4_CKSUM_GOOD PKT_RX_IP_CKSUM_GOOD
PKT_RX_OUTER_L4_CKSUM_UNKNOWN
port 0/queue 0: received 1 packets
src=EC:F4:BB:DC:09:D0 - dst=EC:F4:BB:DB:FC:18 - type=0x0800 - length=142 -
nb_segs=1 - hw ptype: L2_ETHER L3_IPV4 L4_UDP - sw ptype: L2_ETHER L3_IPV4
L4_UDP - l2_len=14 - l3_len=20 - l4_len=8 - Receive queue=0x0
ol_flags: PKT_RX_L4_CKSUM_BAD PKT_RX_IP_CKSUM_GOOD
PKT_RX_OUTER_L4_CKSUM_UNKNOWN
Considering that the checksum for UDP over IPv4 can be optionally
disabled by the sender (although usually computed and transmitted),
is this behavior expected?
For completeness sake, I found an old patch [1] in the ixgbe linux
driver that seems to be related to what I'm seeing. The code changed a
little, but it's still there.
[1]
https://patchwork.ozlabs.org/project/netdev/patch/20090724040031.30202.1531.stgit@localhost.localdomain/
Regards,
Paolo
