In a recent training class the question came up as to whether the Jumbo Frame support for the Cisco ASA was a basic configuration or not. To begin with, lets understand what a Jumbo Frame is, then we can decide.
What Is A Jumbo Frame?
A Jumbo frame is when an Ethernet frame is larger than the standard minimum of 1518 bytes. This includes the Layer 2 header along with the Frame Check Sequence (FCS). The size can increase at times, up to 9216 Bytes. This allows you to transfer more data without processing as many frames. So Jumbo frames improve performance by having less packet overhead, lowering the CPU load in the case of a server, which has the effect of causing fewer interrupts and less delay across the server bus. Jumbo frames are often seen in Data Center Networks.
Example Jumbo Frame Sizes
The size of the frame depends on the headers. The following table offers some examples of frame sizes we may encounter in todays networks.
|Fibre Channel||2148 Bytes|
Use Of The ASA
Based on the above mentioned information, the use of Jumbo Frames in a Data Center would be normal, thus making the configuration of Jumbo Frame support on Data Center networking equipment a basic configuration. So where does the ASA fit into this? Well the ASA is not just an internet edge firewall as many have grown accustomed to. Todays ASA’s are also seen in the data center. There are plenty of documents and design guides that highlight the ASA in the Datacetner (like this one).
Configuring Jumbo Frame Support On The Cisco ASA
To enable Jumbo Frame Support on the Cisco ASA you would perform the following configuration on the CLI:
ASA(config-if)# jumbo-frame reservation ASA(config-if)# exit ASA(config)# mtu g0/1 2148 ASA(config)# wr mem ASA(config)# reload
You should understand that increasing the frame size that the ASA can handle allocates resources to the feature, which might limit the maximum use of other features (Rob from Peter to pay Paul), such as ACLs.
To bring it all back together, Jumbo Frame support in the Cisco ASA would be a “Basic” configuration in the Data Center. Therefore, it’s worth knowing how to configure it, and making it a part of you standard configuration for your Cisco ASA when used in Data Center environments.