Date: Wed, 8 Apr 2026 23:31:53 +0800 From: Zhenlei Huang <zlei@FreeBSD.org> To: Lexi Winter <ivy@FreeBSD.org> Cc: net@freebsd.org Subject: Re: FreeBSD guest on Linux KVM, some vtnet(4) packets don't arrive Message-ID: <28495B68-0BD1-4372-806C-C766DBCB8410@FreeBSD.org> In-Reply-To: <adZocDxDXSBFXQGA@amaryllis.le-fay.org>
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[-- Attachment #1 --] > On Apr 8, 2026, at 10:38 PM, Lexi Winter <ivy@FreeBSD.org> wrote: > > hello, > > i'm using FreeBSD main: > > FreeBSD 16.0-CURRENT #0 main-n284768-e6eba5076929: Mon Mar 30 16:07:28 UTC 2026 > root@releng3.nyi.freebsd.org:/usr/obj/usr/src/powerpc.powerpc64/sys/GENERIC64 > > as a qemu (KVM) guest on a Linux host: > > Linux 6.18.21-0-lts #1-Alpine SMP 2026-04-07 10:34:29 ppc64le > > on the Linux side, qemu is configured to provide a tap interface to the > guest: > > qemu-system-ppc64 \ > -smp cpus=176,sockets=2,cores=22,threads=4 \ > -accel kvm -M pseries -m 8g -nographic -serial mon:stdio \ > -drive file=/vm/ppc64-main/root.img,format=raw,if=virtio \ > -netdev tap,id=net0,ifname=vm-ppc64-main,script=no,downscript=no \ > -device virtio-net-pci,netdev=net0 > > the tap interface looks fine: > > 10: vm-ppc64-main: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000 > link/ether ae:dc:d8:39:be:fa brd ff:ff:ff:ff:ff:ff > inet6 fe80::acdc:d8ff:fe39:befa/64 scope link proto kernel_ll > valid_lft forever preferred_lft forever > inet6 fe80::1/64 scope link > valid_lft forever preferred_lft forever > > on the FreeBSD side, the vtnet interface also looks fine: > > vtnet0: flags=1008843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500 > options=cc00ba<TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,VLAN_HWTSO,LINKSTATE,TXCSUM_IPV6,HWSTATS> > ether 52:54:00:12:34:56 > inet6 fe80::2%vtnet0 prefixlen 64 scopeid 0x1 > media: Ethernet autoselect (10Gbase-T <full-duplex>) > status: active > nd6 options=821<PERFORMNUD,AUTO_LINKLOCAL,STABLEADDR> > > on the host, i can ping fe80::2%vm-ppc64-main: > > PING fe80::2%vm-ppc64-main (fe80::2%10): 56 data bytes > 64 bytes from fe80::2: seq=0 ttl=64 time=14.833 ms > 64 bytes from fe80::2: seq=1 ttl=64 time=12.524 ms So the traffic with link-local addresses looks good. > > then i configured an IP address on lo0 on the guest: > > lo0: flags=1008049<UP,LOOPBACK,RUNNING,MULTICAST,LOWER_UP> metric 0 mtu 16384 > options=680003<RXCSUM,TXCSUM,LINKSTATE,RXCSUM_IPV6,TXCSUM_IPV6> > inet 127.0.0.1 netmask 0xff000000 > inet6 ::1 prefixlen 128 > inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2 > inet6 fd00:0:0:1::b prefixlen 128 > groups: lo > nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL> > > a route exists for this on the host: > > fd00:0:0:1::b via fe80::2 dev vm-ppc64-main proto bird metric 32 pref medium Just to confirm, do you have a reverse route on the guest ? > > when trying to ping this address, on the host, i can see ICMP packets leaving > the tap interface: > > 15:34:39.106898 IP6 fd00:0:0:1::12 > fd00:0:0:1::b: ICMP6, echo request, id 49664, seq 3, length 64 > 15:34:40.106951 IP6 fd00:0:0:1::12 > fd00:0:0:1::b: ICMP6, echo request, id 49664, seq 4, length 64 > > but these packets never arrive on the guest; tcpdump shows nothing. > > however, 'netstat -in' shows that the packets *are* arriving on the guest, > since Ipkts increments for each ICMP packet. it seems like they're just > getting lost somewhere in the network stack. (Ierrs/Oerrs is zero.) That puzzled me a bit. If the net stack sees the arriving packets, then tcpdump shall intercept them correctly. > > does anyone have any ideas what might be causing this? Does `netstat -sp ip6` and `netstat -sp icmp6` show anything unusual ? Best regards, Zhenlei [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- iNUEARYKAH0WIQRj28YmNowGX1isJg7GJJ6Jgbd0XwUCadZ06V8UgAAAAAAuAChp c3N1ZXItZnByQG5vdGF0aW9ucy5vcGVucGdwLmZpZnRoaG9yc2VtYW4ubmV0NjNE QkM2MjYzNjhDMDY1RjU4QUMyNjBFQzYyNDlFODk4MUI3NzQ1RgAKCRDGJJ6Jgbd0 Xz7qAP9QZVFG6HGgNQ9OybIg0DwAvn5dehsRolkTJ6d5tthWuwD/QeoexfmqSWHW SdB65xIe44dZQ/oy8GMU4s0PhOpeEQA= =APpb -----END PGP SIGNATURE-----home | help
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