Interesting use of "AIX Dead Gateway Detection" with SEA Failover. From the IBM PowerVM Virtualization Introduction and Configuration Redbook:

http://www.redbooks.ibm.com/abstracts/sg247940.html

Page 400:

There are basically four different cases that will initiate a SEA failover:

1. The standby SEA detects that keep-alive messages from the active SEA are
no longer received over the control channel.

2. The active SEA detects that a loss of the physical link is reported by the
physical Ethernet adapter.s device driver.

3. On the Virtual I/O Server with the active SEA, a manual failover can be
initiated by setting the active SEA to standby mode.

4. The active SEA detects that it cannot ping a given IP address anymore.
An end of the keep-alive messages will occur when the Virtual I/O Server with
the primary SEA is shut down or halted, has stopped responding, or has been
deactivated from the HMC.

Important: The Shared Ethernet Adapters must have network interfaces, with
IP addresses associated, to be able to use this periodic reachability test.
These IP addresses have to be unique and you have to use different IP
addresses on the two SEAs.

Important: You might experience up to a 30-second delay in failover when
using SEA failover. The behavior depends on the network switch and the
spanning tree settings. Any of the following three hints can help in reducing
this delay to a minimum:

- For all AIX client partitions, set up Dead Gateway Detection (DGD) on the default route:

	a. Set up DGD on the default route:

	# route change default -active_dgd

	b. Add the command route change default -active_dgd to the /etc/rc.tcpip file to make this change permanent.

	c. Set interval between pings of a gateway by DGD to 2 seconds (default is 5 seconds, setting this parameter to 1 or 2 seconds will allow faster recovery):

	# no -p -o dgd_ping_time=2

- On the network switch, enable PortFast if Spanning Tree is on or disable Spanning Tree.

- On the network switch, set the channel group for your ports to Active if they are currently set to Passive.


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SEA Failback

Action

enable "portfast trunk" on the switch ports (before it was just portfast without "trunk")
activate Dead Gateway Detection and use a ping time of 2 seconds

Result

failback times were up to 50 seconds now they are always below 10 seconds.