Re: HMC to Rack communcations

Latest from IBM but I am waiting on my network guy's response.

I can ping smaller MTU sizes. 1500 is freaking huge and causes issues.

<snip>
Hello Rob,

Below is what the product engineering team has to say.

There is no supported way to tell the HMC to allow the fragment nor to
lower the MTU size from 1500. Hacking the HMC with an incorrect MTU could
lead to other network related problems, specifically, high packet
fragmentation with other network hosts using the correct MTU value.

1500 is the correct MTU value for ethernet networks as defined in RFC
1191. Path-MTU discovery is the mechanism used to determine the actual MTU
for any given connection. If Path-MTU discovery is not working in your
network, then that is the problem that needs to be corrected.

You will need to work with your network team to configure your firewall to
prevent it from dropping ICMP traffic, which prevents path MTU discovery
from working. These firewalls should be changed to allow ICMP
Fragmentation-DF-Set (ICMP type 3, code 4) packets so that path MTU
discovery will work.

If you would like a new feature added to make the MTU changes you desire
to be implemented, you can submit a request for enhancement (RFE).

You can access the following site and provide feedback regarding HMC
support for further comments to IBM:

https://www.ibm.com/developerworks/rfe/

Follow the instructions at that site to submit a new request.

Click on the "Submit" tab.
Log in with your IBM id when prompted.
Fill out all mandatory fields and any applicable optional fields as
instructed.
To ensure proper routing of the HMC request select the following product
information:
How do you want to specify the product: I want to specify the brand,
product family, and product
Brand:* Servers and Systems Software
Product family:* Power Systems
Product:* Power Hardware Management Console
</snip>


Rob Berendt