> On 15. Sep 2025, at 14:59, Karl Denninger <k...@denninger.net> wrote: > > Hmmmmm.... just came in via git pull: > commit ffd956a3918cd5e64c8850eb77247428a29f7221 > Author: Michael Tuexen <tue...@freebsd.org> > Date: Wed Sep 10 17:13:35 2025 +0200 > > dhclient: improve UDP checksum handling > > When sending UDP packets: > * compute the checksum in the correct order. This only has an impact > if the length of the payload is odd. > * don't send packet with a checksum of zero, use 0xffff instead as > required. > When receiving UDP packets: > * don't do any computations when the checksum is zero. > * compute the checksum in the correct order. This only has an impact > if the length of the payload is odd. > * when computing the checksum, store the pseudo header checksum > * if the checksum is computed as zero, use 0xffff instead. > * also accept packets, when the checksum in the packet is the pseudo > header checksum. > The last point fixes a problem when the DHCP client runs in a VM, > the DHCP server runs on the host serving the VM and the network > interface supports transmit checksum offloading. Since dhclient > doesn't use UDP sockets but bpf devices to read the packets, the > checksum will be incorrect and only contain the checksum of the > pseudo header. > > This could potentially apply to other bpf-using things -- which includes > dhcpcd. And you have tso/lro turned on. Hi Karl,
this is true. Do we have an dhcpd in-tree? Or are you aware of other in-tree programs which use UDP via bpf and not via the socket interface? Best regards Michael > It is a patch to dhclient, not dhcpcd but does the same issue potentially > apply? > On 9/14/2025 13:00, Karl Denninger wrote: >> On 9/14/2025 12:38, Chris Ross wrote: >>> >>>> On Sep 14, 2025, at 12:29, Karl Denninger <k...@denninger.net> wrote: >>>> Rolling this around in my head some more..... what is the underlying >>>> interface? >>>> I ask because I saw this happen with "re" driver interfaces (both IPv4 and >>>> 6) where it would not get an ARP map and thus couldn't see anything at all >>>> on the outside - there were enough other screwball things going on with >>>> the "re" driver (timeouts and similar) that I tossed that and now run on >>>> ix and a couple of SFP+ transceivers which has been entirely-stable >>>> (although igb also appears to work as I've gotten my hands on a box with a >>>> couple of those and tested that too.) >>>> >>> In my case it’s an ix. Connected to a 1gbps switch interface, but an ix >>> interface. And, the same hardware that was doing this fine a few months ago. >>> >>> vlan0: flags=1008843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST,LOWER_UP> >>> metric 0 mtu 1500 >>> options=4600703<RXCSUM,TXCSUM,TSO4,TSO6,LRO,RXCSUM_IPV6,TXCSUM_IPV6,MEXTPG> >>> ether a4:53:0e:79:b9:82 >>> inet A.B.C.D netmask 0xffffff00 broadcast A.B.C.255 >>> inet6 fe80::6e8:e675:f359:3465%vlan0 prefixlen 64 scopeid 0x4 >>> groups: vlan >>> vlan: 6 vlanproto: 802.1q vlanpcp: 0 parent interface: ix0 >>> media: Ethernet autoselect (1000baseT <full-duplex>) >>> status: active >>> nd6 options=1<PERFORMNUD> >>> >>> ix0: flags=1008843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST,LOWER_UP> metric >>> 0 mtu 1500 >>> options=4e53fbb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,TSO4,TSO6,LRO,WOL_UCAST,WOL_MCAST,WOL_MAGIC,VLAN_HWFILTER,VLAN_HWTSO,RXCSUM_IPV6,TXCSUM_IPV6,HWSTATS,MEXTPG> >>> ether a4:53:0e:79:b9:82 >>> media: Ethernet autoselect (1000baseT <full-duplex>) >>> status: active >>> nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL> >>> >>> >> If you find anything a note back here would be greatly excellent. I do note >> that per the various notes from long ago I have both tso and lro turned off >> (but I use ipfw, which is where that apparently comes from) on the outside >> interface -- but I doubt that is involved as I did try with it on and it >> didn't change anything. >> >> -- >> Karl Denninger >> k...@denninger.net >> The Market Ticker >> [S/MIME encrypted email preferred] > -- > Karl Denninger > k...@denninger.net > The Market Ticker > [S/MIME encrypted email preferred]
