Installation guide

address from DHCP or boot using the PXE protocol, or both. There are two common causes
of this error: having a long forward delay time set for the bridge, and when the iptables
package and kernel do not support checksum mangling rules.
Lo n g f o rward d elay t ime o n b rid g e
In vest ig at io n
This is the most common cause of this error. If the guest network
interface is connecting to a bridge device that has STP (Spanning Tree
Protocol) enabled, as well as a long forward delay set, the bridge will
not forward network packets from the guest virtual machine onto the
bridge until at least that number of forward delay seconds have elapsed
since the guest connected to the bridge. This delay allows the bridge
time to watch traffic from the interface and determine the MAC addresses
behind it, and prevent forwarding loops in the network topology.
If the forward delay is longer than the timeout of the guest's PXE or
DHCP client, then the client's operation will fail, and the guest will either
fail to boot (in the case of PXE) or fail to acquire an IP address (in the
case of DHCP).
So lu t io n
If this is the case, change the forward delay on the bridge to 0, or
disable STP on the bridge.
Note
This solution applies only if the bridge is not used to connect
multiple networks, but just to connect multiple endpoints to a
single network (the most common use case for bridges used by
lib virt ).
If the guest has interfaces connecting to a lib virt -managed virtual
network, edit the definition for the network, and restart it. For example,
edit the default network with the following command:
# virsh net-edit default
Add the following attributes to the <bri d g e> element:
<name_of_bridge='virbr0' d el ay= ' 0 ' stp= ' o n' />
Note
d el ay= ' 0 ' and stp= ' o n' are the default settings for virtual
networks, so this step is only necessary if the configuration has
been modified from the default.
If the guest interface is connected to a host bridge that was configured
outside of lib virt , change the delay setting.
Add or edit the following lines in the /etc/sysco nfi g /netwo rk-
Red Hat Ent erp rise Linux 6 Virt ualiz at ion Host Configurat ion and G uest Inst allat ion G uide
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