Re: Load balancing IP connections

Mike -

Is the subnet mask for the 10.1.1.1 interface set to 255.255.255.255 ?   My
guess is that it's not.    That would explain why you can't ping any 10.1.1
hosts unless you specify a particular local interface.   Leaving the local
interface unspecified on the PING command would allow the TCP/IP code to
(incorrectly) conclude it can reach 10.1.1.11 from 10.1.1.1.   By restricting
the mask to 255.255.255.255, TCP/IP will only  pick 10.1.1.1 as the local
interface if the destination is also 10.1.1.1.  Otherwise, it will pick 10.1.1.2
or 10.1.1.3, which is what you want.

As for not being able to directly ping 10.1.1.1, that is "correct".   VirtualIP
interfaces are not directly routable.  That is, you cannot directly reach a
VirtualIP interface.   It  can only be reached indirectly via one of the
"physical  IP interfaces", in your case, 10.1.1.2 and 10.1.1.3.

The most common environment for VirtualIP with load balancing & fault tolerance
is to have the VirtualIP interface configured on a different subnet than the
locally attached subnet.    Local clients know the AS/400 by the physical  IP
interfaces, but remote clients, coming in through a gateway , know the AS/400
only by its VirtualIP address.  The local gateway has routes defined (either
manually or via RouteD) telling it that the VirtualIP address is reachable via
any  of the physical  IP interfaces.

If you also want your local clients access the VirtualIP interface, the 10.1.1.1
shoud be changed to an address on another subnet (192.1.1.1?)  and then the
routes need to be advertised or configured that the new VirtualIP address is
reachable via 10.1.1.2 or 10.1.1.3.

I've got a few Lotus Freelance charts that describe this a bit better.  I'll
send you a copy.   If you still have questions, feel free to e-mail me directly.

And yes, more detailed documentation is underway.

Gary Diehl

AS/400 TCP/IP Development
Endicott, NY, 13760
Phone: 607-752-5505 or Tie Line: 852-5505.  FAX: 607-752-5421
Alternate e-mail:   INTERNET: gdiehl@vnet.ibm.com     VM: GDIEHL@RCHVMV2

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To:   midrange-l@midrange.com
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Subject:  Load balancing IP connections




Hi All,

I am trying to configure TCP on a machine with 2 ethernet cards so that I can
use a single IP address for load balancing and redundancy.  Reading the help for
the ADDTCPIFC command LCLIFC parameter implies that I need to do the following:

1. Create interface 10.1.1.1 as line description *VIRTUALIP
2. Create interface 10.1.1.2 against line ETHERNET1 with LCLIFC(10.1.1.1)
3. Create interface 10.1.1.3 against line ETHERNET2 with LCLIFC(10.1.1.1)

After configuring and starting these interfaces, I cannot ping '10.1.1.11'
unless I specify one of the physical interfaces and I
cannot ping 10.1.1.1 but I can ping 10.1.1.2 and 10.1.1.3 from a PC.
Has anyone successfully managed to configure an AS/400 with this sort of setup?
If so, what am I doing wrong?

The manuals are less than forthcoming on using *VIRTUALIP.

The AS/400 is running v430 and on Cume pack 9131.  I cannot find anything on the
support pages with respect to this setup.


Thanks,

Mike Buglass
mike_buglass@csiltd.co.uk
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