Hi all: I have some kvm host(rhel 6.4, 2.6.32-358.0.1.el6.x86_64), I ran several windows guest on it(more than 10 guest on one host and the guest os are win7-32/win7-64/win2k8), but the guest network kept down automatically, lost package. I tried virtio drive and e1000 drive,but it didn't work. However, when I run cmd.exe ping some other subnet ip it worked. The host and guest are connected by bridge. Here is some configure infomation of my guest: <interface type='bridge'> <mac address='aa:aa:aa:49:39:71'/> <source bridge='kvmbr3'/> <model type='e1000'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </interface> brctl show as follow: kvmbr28000.b8ca3a5cbea2noeth2 vnet0 vnet11 vnet13 vnet15 vnet17 vnet19 vnet2 vnet21 vnet23 vnet25 vnet27 vnet29 vnet5 vnet7 vnet9 The /etc/sysctl.conf configure as follow: # Kernel sysctl configuration file for Red Hat Linux # # For binary values, 0 is disabled, 1 is enabled. See sysctl(8) and # sysctl.conf(5) for more details. # Controls IP packet forwarding net.ipv4.ip_forward = 0 #net.ipv4.ip_forward = 1 # Controls source route verification net.ipv4.conf.default.rp_filter = 1 # Do not accept source routing net.ipv4.conf.default.accept_source_route = 0 # Controls the System Request debugging functionality of the kernel kernel.sysrq = 0 # Controls whether core dumps will append the PID to the core filename. # Useful for debugging multi-threaded applications. kernel.core_uses_pid = 1 # Controls the use of TCP syncookies net.ipv4.tcp_syncookies = 1 # Disable netfilter on bridges. # Controls the default maxmimum size of a mesage queue kernel.msgmnb = 65536 # Controls the maximum size of a message, in bytes kernel.msgmax = 65536 # Controls the maximum shared segment size, in bytes kernel.shmmax = 68719476736 # Controls the maximum number of shared memory segments, in pages kernel.shmall = 4294967296 ########### add by operation V1.0 begin ############ net.ipv4.ip_local_port_range = 32768 65000 net.core.rmem_max = 8388608 net.core.wmem_max = 8388608 net.ipv4.tcp_rmem = 4096 87380 8388608 net.ipv4.tcp_wmem = 4096 65536 8388608 net.ipv4.tcp_max_syn_backlog = 8192 net.ipv4.tcp_window_scaling = 0 net.ipv4.tcp_sack = 0 net.ipv4.tcp_timestamps = 0 kernel.panic = 5 vm.swappiness = 51 ########### add by operation V1.0 end ############ net.bridge.bridge-nf-call-ip6tables = 0 net.bridge.bridge-nf-call-iptables = 0 net.bridge.bridge-nf-call-arptables = 0 #add by wdh #net.ipv4.conf.all.proxy_arp = 1 Best Regards, cochen