TlDR: If you are using DHCP and you want to permanently set the MTU for your instance, edit your DHCP client config.

If you read our first article on setting the MTU on an EC2 instance for Amazon Redshift usage, then you may want to read this as well. After using the commands in the first article, we noticed that after some time, our instances had their MTU set back to 9001. We realized this was due to MTU settings being sent by the DHCP server since that is the default for these instances (C3, M3, etc). We then set out to edit all our Chef recipes to deploy our new DHCP client configuration files so we can quickly deploy them to all our instances.

Here is what should be added to the /etc/dhcp/dhclient.conf (on Ubuntu Precise LTS):

#added these two lines before the request line
default interface-mtu 1500; supersede interface-mtu 1500;

When adding this to the dhclient.conf file, it will override an MTU setting of 1500 to the interface that's set for DHCP. Hope this helps someone!

About Inc. formerly known as Hapyrus Inc., is a Dave McClure’s 500 Startups graduate, headquartered in Palo Alto, California. provides software that automates data replication to Amazon Redshift. If you'd like to simplify your BI analytics backend, let us know.