The combination in $subject apparently stopped working -- I'm running 3.0-rc6 kernel on host where it doesn't work. The setup is -- a bridge, br0, to which host eth0 and guest tap devices are connected. When KVM guest boots, it tries to send DHCP requests to its ethernet device (it does not matter which device it uses - be it virtio or e1000 or rtl8139, all work the same). These requests appears (can be seen) on the tap device, but they never propagate to bridge. Example of a packet as seen on the tap device from a windows7 guest: # tcpdump -npvi tap-kvm port bootpc tcpdump: WARNING: tap-kvm: no IPv4 address assigned tcpdump: listening on tap-kvm, link-type EN10MB (Ethernet), capture size 65535 bytes 13:38:21.435032 IP (tos 0x0, ttl 128, id 109, offset 0, flags [none], proto UDP (17), length 328) 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 52:54:00:12:34:56, length 300, xid 0xdc8f28b1, secs 7168, Flags [Broadcast] Client-Ethernet-Address 52:54:00:12:34:56 Vendor-rfc1048 Extensions Magic Cookie 0x63825363 DHCP-Message Option 53, length 1: Discover Client-ID Option 61, length 7: ether 52:54:00:12:34:56 Hostname Option 12, length 7: "mjt-006" Vendor-Class Option 60, length 8: "MSFT 5.0" Parameter-Request Option 55, length 12: Subnet-Mask, Domain-Name, Default-Gateway, Domain-Name-Server Netbios-Name-Server, Netbios-Node, Netbios-Scope, Router-Discovery Static-Route, Classless-Static-Route, Classless-Static-Route-Microsoft, Vendor-Option Exactly the same thing happens with 4 different DHCP clients: it's ipxe boot rom (network booting of a KVM guest), win7 built-in DHCP client, udhcpc and dhcp3. All other traffic - so far anyway - works correcty. Right now I don't have time to debug the issue, will try to bisect later. But if anyone have pointers or thoughts, please shot away ;) Thanks! /mjt -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html