XEN: reattaching network devices after the network bridge is restarted

This document (7001931) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 10 SP2
SUSE Linux Enterprise Server 10 SP1

Situation

After a restart of the networking subsystem or a restart of the Xen bridge, Xen DomU's are not able to access the network.

Resolution

This issue is commonly seen where the network bridge has been shutdown or the entire network subsystem has been restarted. It is not recommended to stop and the restart the network subsystem while DomU's are running. However in the event that this is done, the recover is pretty straight forward. Alternatively, you may elect to simply restart the DomU.

Each virtual NIC essentially also has a "virtual cable." The cable is attached to a network bridge in Dom0. When the bridge is stopped, the virtual cable is unplugged. In order to reattach the cable, the bridge and the end of the cable need to be identified.

The method of re-attaching the virtual NIC to the bridge device is the same regardless of whether or not the DomU is para-virtual or fully virtual.

Identify the bridge that the DomU is supposed to be attached to. Replace "DOMU" with the name or ID of the DomU in question.

xm list -l DOMU | grep bridge
Example output:
(bridge eth0)
Identify what virtual NIC (cable) the DomU is attached to:
xm network-list DOMU
Example output:
```
Idx BE     MAC Addr.     handle state evt-ch tx-/rx-ring-ref BE-path
```
```
0   0  00:16:3e:21:7d:2a    0     4      11    520  /521     /local/domain/0/backend/vif/34/0
```
The bolded part of the output defines the VIF device. In this case it would be "vif32.0". To convert it simply remove the first slash and replace the last slash with a period.
Attach the VIF device identified in step 2 to the bridge identified in step 1
syntax: brctl addif BRIDGE VIF
example: brctl addif br0 vif34.0

Disclaimer

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