Re: AS/400 Multiple Ethernet Controllers

[Gary Diehl <gdiehl@xxxxxxxxxxxx>]

Various responses have been posted to the question, "advantages of
having more than 1 Lan Card in an AS/400 system."   There have been good
replies mentioning NAT, DNS and subnet based load balancing, and fault
tolerance as possible reasons.

Along the load balancing and fault tolerance fronts, there are a few
more options.

Load balancing via multiple DNS A-record entries is certainly possible. 
 But TCP/IP on the AS/400 also supports a similar, "Duplicate Route
Round Robin" load balancing scheme.  It's TCP/IP route, rather than DNS,
based.   It allows you to configure a pool of equivalent routes, each
bound to a different adapter, and use a round robin scheme to select a
route/adapter for outbound data.  One configuration allows you to direct
inbound traffic to one adapter and outbound traffic to different
adapter(s).  

For even more load balancing power, you can use a front end dispatcher
like the IBM Network Dispatcher to distribute connections over multiple
adapters on a single server, or across multiple servers.   This is a
common load balancing technique for high volume web servers.   This
method of load balancing requires the *VIRTUALIP support in V4R3 and
higher OS/400 releases.

As for fault tolerance, you can have your external clients connect to a
single *VIRTUALIP address through any number of physical adapters.  That
way, if one or more adapters fails, so long as at least one adapter
stays active, your system stays available to the clients.

Formal documentation is a bit sparse on these topics.  I do have a Lotus
Freelance presentation that discusses things in a bit more detail.   If
anyone ways a copy, e-mail me at diehl@us.ibm.com.



Gary A. Diehl 
AS/400 TCP/IP Development
IBM Corporation, Endicott, New York.  13760   
Phone: 607-752-5505 or Tie Line: 852-5505.   FAX: 607-752-5421 
INTERNET: gdiehl@vnet.ibm.com    or  diehl@us.ibm.com
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