Description of problem: boot guest with e1000 nic, change the MTU of guest nic and tap device to 16110 (max MTU of e1000 nic), and added an arp entry on host, then ping guest from host, ping failed. # ping $guest_ip -I interface -s 16082 -M do Version-Release number of selected component (if applicable): kvm-83-232.el5 How reproducible: 100% Steps to Reproduce: 1. boot guest with e1000 nic cmd: qemu-kvm -drive file='/home/images/RHEL-Server-6.0-32.qcow2',index=0,if=ide,media=disk,cache=none,format=qcow2 -net nic,vlan=0,model=e1000,macaddr='9a:a8:28:b8:e4:93' -net tap,vlan=0,ifname='t0-033040-H5Lp',script='/home/qemu-ifup-switch',downscript='no' -m 8192 -smp 4,cores=1,threads=1,sockets=4 -cpu qemu64,+sse2 -soundhw ac97 -vnc :0 2.Change MTU of guest nic and $tap guest)# ifconfig eth0 mtu 16610 host)# ifconfig $tap 16610 3. Add a arp entry on host # arp -s $guest_ip $guest_mac -i $tap 4. Ping guest from host (16110-28=16082, 16110 is max mtu of e1000) #ping $guest_ip -I $tap -s 16082 -M do Actual results: could not ping guest successfully Expected results: Additional info: 1. host: kernel : 2.6.18-259.el5 2. guest: rhel6.0.32
Why is the arp step necessary ? I don't think manually tweaking the arp cache would be necessary for that. Did you try not doing it ?
(In reply to comment #1) > Why is the arp step necessary ? I don't think manually tweaking the arp cache > would be necessary for that. > > Did you try not doing it ? I can reproduce it without arp
Jason, If it doesn't work after the backport, then we need to recondider the dev-ack. Thanks, Ronen.
Reproduced on kvm-83-239.el5 + kernel-2.6.18-274.el5. Steps: 1. boot guest with e1000 nic cmd: /usr/libexec/qemu-kvm -drive file=/home/RHEL-Server-6.0-32.qcow2,index=0,if=ide,media=disk,cache=none,format=qcow2 -net nic,vlan=0,model=e1000,macaddr=9a:a8:28:b8:e4:93 -net tap,ifname=aa-bb-cc,vlan=0,script='/etc/qemu-ifup',downscript='no' -m 2048 -smp 4,cores=1,threads=1,sockets=4 -vnc :10 -cpu qemu64,+sse2 -monitor stdio -boot c 2.Change MTU of guest nic and $tap guest)# ifconfig eth2 mtu 16610 host)# ifconfig aa-bb-cc 16610 3. Add a arp entry on host # arp -s 10.66.9.153 9a:a8:28:b8:e4:93 -i aa-bb-cc 4. Ping guest from host #ping -I aa-bb-cc -s 16082 -M do Result: Ping failed. Verified the bug on kvm-83.143.el5 + kernel-2.6.18-296 with the same steps as above. After step 4, can ping the guest from host successfully. So, this issue is fixed.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHSA-2012-0149.html