> On 27. Sep 2025, at 18:26, John Nielsen <[email protected]> wrote: > >> On Sep 26, 2025, at 3:44 PM, Michael Tuexen >> <[email protected]> wrote: >> >>> On 26. Sep 2025, at 20:52, John Nielsen <[email protected]> wrote: >>> >>>> On Sep 26, 2025, at 1:46 AM, Michael Tuexen >>>> <[email protected]> wrote: >>>> >>>>> >>>>> On 26. Sep 2025, at 02:58, John Nielsen <[email protected]> wrote: >>>>> >>>>> Not sure if this is a known issue or even an issue on the FreeBSD side >>>>> but decided to ask here first. I’m happy to put in a bug report if >>>>> appropriate. >>>>> >>>>> I have a hypervisor machine running Arch Linux with KVM, Qemu and >>>>> libvirtd. The machine has a Chelsio T520-CR adapter. I recently began >>>>> passing through virtual functions of the NIC to several of the guests I >>>>> run on the hypervisor. One of the guests runs Windows 11, and the change >>>>> was seamless. Two of the guests are running FreeBSD (14.3 or so). On each >>>>> of them the VFs were readily identified and configured (using DHCP in one >>>>> case), and ping and ARP appeared to work fine. However, TCP and UDP >>>>> traffic to the guests never received a response. After some >>>>> head-scratching and troubleshooting I discovered that running “ifconfig >>>>> cxlv0 -rxcsum” immediately allowed traffic to flow as expected. >>>> >>>> I don't have access to such a network card. Just to be clear: you are >>>> running the “ifconfig cxlv0 -rxcsum” command inside the guest running >>>> FreeBSD, right? >>> >>> Yes. >>> >>>> What is the peer, when you mention TCP and UDP do not work? Is it the host >>>> running Linux? Is it another VM? Is it some external host? >>> >>> My laptop on the same subnet primarily, but. Also tested from another >>> physical machine running FreeBSD. >> OK. That does not seem to be related to what I initially thought. >> >> Could you run >> tcpdump -i outgoing_interface -w laptop.pcap >> on your laptop and >> tcpdump -i cxlv0 -w vm.pcap >> on your vm at the same time and try to do some TCP based communication. >> Maybe two times, one time with ifconfig cxlv0 rxcsum and one time with >> ifconfig cxlv0 -rxcsum. >> >> If you are fine with doing the measurements, you can send the .pcap files >> to [email protected] <mailto:[email protected]>. >> >> At least I would like to understand what is going on. > > Thank you, I sent you those packet captures under separate cover. Thanks I got the email and sent a response. > > From what I can tell so far the VM does receive incoming packets even when > rxcsum is enabled, and the checksums appear correct at least according to > tcpdump. But something prevents the packets from being processed or sent up > the stack. The VM’s sshd never generates a SYN/ACK in response to a > connection attempt. A DNS query from the VM looks like it gets a response on > the wire but the response doesn’t make it to the process doing the query. Yes, I agree. For whatever reason the packets received, but are not delivered to the transport stack. I would like to figure out where the packets are dropped or stored and not processed further. I sent you some suggestions to try. I hope we can figure out where the problem is related. In addition to what I suggested, you might want to provide the output of netstat -s from before and after running the experiment.
Best regards Michael > > -John >
