Hi!
I am trying DHCP between 2 guests. So I am running first guest with:
-netdev tap,id=TAP0,helper=/home/aik/qemu-bridge-helper \
-device "virtio-net-pci,id=vnet0,mac=C0:41:49:4b:ee:ee,netdev=TAP0"
and second one with:
-netdev tap,id=TAP0,vhost=on,helper=/home/aik/qemu-bridge-helper \
-device "virtio-net-pci,id=vnet0,mac=C0:41:49:4b:00:01,netdev=TAP0" \
Both tap are connected to br0 on the host:
aik@fstn1-p1:~$ brctl show
bridge name bridge id STP enabled interfaces
br0 8000.fe397c73cecc no tap0
tap1
Both guests are debian8 with v4.7 kernel, one is running Dnsmasq version
2.72, the other - isc-dhclient-4.3.1.
The very first response from dnsmasq has a bad UDP checksum:
04:19:04.946754 c0:41:49:4b:ee:ee > c0:41:49:4b:00:01, ethertype IPv4 (0x0800)
, length 346: (tos 0xc0, ttl 64, id 60635, offset 0, flags [none], proto UDP (
17), length 332)
192.168.1.250.67 > 192.168.1.1.68: [bad udp cksum 0x8595 -> 0x6e44!] BOOTP
/DHCP, Reply, length 304, xid 0x38e6b51c, Flags [none] (0x0000)
0x8595 looks like a UDP header checksum. Unlike dhclient (which uses
PF_PACKET), dnsmasq seems to use AF_INET and DGRAM so I am wondering what
exactly should do this checksum calculations in this case and why it does
not do this?
I read the old discussion at
http://www.mail-archive.com/kvm@vger.kernel.org/msg41958.html
but it seems that in my case the broken thing is dnsmasq (which is hard to
believe). Running the dnsmasq's guest with
-device virtio-net-pci,id=vnet0,csum=off,...
fixes the problem.
What is broken now? Thanks.
--
Alexey
