I've set up some interconnected qemu VMs to test out port forwarding rules. For now, my current blocker is much simpler and has nothing to do with port forwarding. When I send a UDP packet from a go program through the Linux OS, it is flagged as having a bad checksum by tcpdump on the interface from within the OS itself (before it has even gone through any bridging/gateways/etc). Is this expected/normal? Is there a fix for it?
16:37:22.899722 IP (tos 0x0, ttl 64, id 9829, offset 0, flags [DF], proto UDP ()
192.168.0.2.36793 > 22.22.22.22.20000: [bad udp cksum 0xecf9 -> 0x989f!] UD0
0x0000: 0200 0000 0202 0200 0000 0401 0800 4500
0x0010: 0026 2665 4000 4011 278c c0a8 0002 1616
0x0020: 1616 8fb9 4e20 0012 ecf9 5049 4e47 5f42
0x0030: 5954 4553
For additional context, the networking device that the packet is going through is pci virtio, connected to a tap device.
Editing to add the output of ethtool -k:
# ethtool -k eth1
Features for eth1:
rx-checksumming: on [fixed]
tx-checksumming: on
tx-checksum-ipv4: off [fixed]
tx-checksum-ip-generic: on
tx-checksum-ipv6: off [fixed]
tx-checksum-fcoe-crc: off [fixed]
tx-checksum-sctp: off [fixed]
scatter-gather: on
tx-scatter-gather: on
tx-scatter-gather-fraglist: off [fixed]
tcp-segmentation-offload: on
tx-tcp-segmentation: on
tx-tcp-ecn-segmentation: on
tx-tcp-mangleid-segmentation: off
tx-tcp6-segmentation: on
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off [fixed]
rx-vlan-offload: off [fixed]
tx-vlan-offload: off [fixed]
ntuple-filters: off [fixed]
receive-hashing: off [fixed]
highdma: on [fixed]
rx-vlan-filter: on [fixed]
vlan-challenged: off [fixed]
tx-lockless: off [fixed]
netns-local: off [fixed]
tx-gso-robust: on [fixed]
tx-fcoe-segmentation: off [fixed]
tx-gre-segmentation: off [fixed]
tx-gre-csum-segmentation: off [fixed]
tx-ipxip4-segmentation: off [fixed]
tx-ipxip6-segmentation: off [fixed]
tx-udp_tnl-segmentation: off [fixed]
tx-udp_tnl-csum-segmentation: off [fixed]
tx-gso-partial: off [fixed]
tx-tunnel-remcsum-segmentation: off [fixed]
tx-sctp-segmentation: off [fixed]
tx-esp-segmentation: off [fixed]
tx-udp-segmentation: off [fixed]
tx-gso-list: off [fixed]
fcoe-mtu: off [fixed]
tx-nocache-copy: off
loopback: off [fixed]
rx-fcs: off [fixed]
rx-all: off [fixed]
tx-vlan-stag-hw-insert: off [fixed]
rx-vlan-stag-hw-parse: off [fixed]
rx-vlan-stag-filter: off [fixed]
l2-fwd-offload: off [fixed]
hw-tc-offload: off [fixed]
esp-hw-offload: off [fixed]
esp-tx-csum-hw-offload: off [fixed]
rx-udp_tunnel-port-offload: off [fixed]
tls-hw-tx-offload: off [fixed]
tls-hw-rx-offload: off [fixed]
rx-gro-hw: on
tls-hw-record: off [fixed]
rx-gro-list: off
macsec-hw-offload: off [fixed]
rx-udp-gro-forwarding: off
hsr-tag-ins-offload: off [fixed]
hsr-tag-rm-offload: off [fixed]
hsr-fwd-offload: off [fixed]
hsr-dup-offload: off [fixed]
