Red Hat Bugzilla – Bug 705317
Failed to ping guest(rhel4.9) after change virtio MTU
Last modified: 2011-05-18 09:28:51 EDT
Description of problem:
I booted up a rhel4.9 guest with virtio nic, change the MTU of guest nic and tap device to 65520 (max MTU of virtio nic), and added an arp entry on host, then ping guest from host, but it was failed.
Version-Release number of selected component (if applicable):
this problem happened in rhel4.9-32/64/PAE
Steps to Reproduce:
1. boot guest with virtio nic by cmd
2. Change MTU of guest nic and $tap
guest)# ifconfig eth0 mtu 65520
host)# ifconfig $tap mtu 65520
3. Add a arp entry on host
# arp -s $guest_ip $guest_mac -i $tap
4. Ping guest from host (65520-28=65492, 65520 is max mtu of virtio)
#ping $guest_ip -I $tap -s 65492 -M do
could not ping guest successfully
can ping guest successfully
/usr/libexec/qemu-kvm -drive file='RHEL-4.9-PAE-virtio.raw',index=0,if=ide,media=disk,cache=none,format=raw -net nic,vlan=0,model=virtio,macaddr='9a:85:ef:26:a1:34' -net tap,vlan=0,ifname='t0-134629-2A7D',script='/etc/qemu-ifup-switch',downscript='no' -m 4096 -smp
2,cores=1,threads=1,sockets=2 -cpu qemu64,+sse2 -soundhw ac97 -vnc :0 -rtc-td-hack -M rhel5.6.0 -boot c -usbdevice tablet -no-kvm-pit-reinjection
This is due to lack of jumbo frame support in RHEL4.
Due to schedule constraints, we don't plan to fix it.
For more information, see 633195, opened against 6.1