In this lesson,
we're going to cover the maximum transmission unit.
The maximum transmission unit, or MTU,
refers to the largest size of a frame
that can be sent over a network.
The frame size is measured in bytes,
and the frame size dictates how much data can be sent
and processed by a network
inside of a single transaction or transmission.
Personally, I like to think
about the maximum transmission unit
as the maximum load capacity
for your frames inside of your network.
For example, in the real world,
you might walk into an elevator in a high rise building,
and you can see a sign that says,
"Maximum capacity, 10 people," or 2,500 pounds.
And this is the equivalent
of your maximum transmission unit size.
If you try to put more than 10 people
or more than 2,500 pounds in that elevator,
it probably won't work, or,
it would cause some kind of strange issues,
just like if you try to put more data into a frame
than it's designed to hold.
Now, when we talk about a maximum transmission unit,
it's really important that you realize
that these MTUs will impact the performance
and efficiency of your network.
A properly configured MTU will ensure that the data packets
and frames are neither too large or too small.
If you set the MTU too high, then your packets
and frames may be too large for the network to handle,
and this can lead to packet loss
and the need for data to be remitted.
On the other hand, if you set the MTU too small,
the network will experience increased overhead
due to the larger number of packets that need to be sent,
which can also slow down
your network's maximum transmission data speed too.
Now, the MTU size that you're going to configure
is going to depend on the type of network
and the type of traffic
that you're trying to support.
If you're using a wired ethernet network,
the standard or default MTU size is 1500 bytes.
This size is generally considered acceptable in the industry
because it balances out the efficiency
and compatibility requirements across many different types
of network equipment and internet pathways
without causing any issues.
Now, if you're using a wireless network, though,
you may need to use a smaller MTU size.
The smaller size is often required
because our wireless networks are inherently unstable
and they have higher error rates during their communication.
So using a larger MTU size could lead to larger packets
with increased retransmission rates too,
and that's why we like to use a smaller size
when we're dealing with wireless networks.
Now, if you're going to be using a virtual private network
or a point-to-point protocol over ethernet connection,
known as a PPPoE,
you may need to configure your devices
to use a smaller MTU size.
This is because both the VPN
and PPPoE connections will utilize an encapsulation process
that add extra headers to the packets,
and this reduces the remaining space available
for the actual data payload inside of the frame.
Personally, when I set up A VPN or a PPPoE connection,
I tend to configure my MTU size
to something between 1400 and 1450 bytes in size.
Now, this leaves enough room
for the additional overhead required
when I'm forwarding the VPN or PPPoE frames
out to the rest of my network.
The final MTU configuration you need to be aware of
is known as a jumbo frame.
Now, a jumbo frame simply refers to any frame
that exceeds the standard
or default ethernet MTU size of 1500 bytes.
While a jumbo frame can be any frame larger than 1500 bytes,
generally, you're going to see that our jumbo frames
are configured to use the default size
of 9000 bytes instead.
These larger 9000 byte frames are beneficial
when working in storage area networks
because they can enhance the efficiency
of your data transfers by reducing your overhead.
This occurs because more data is being sent inside
of a single jumbo frame,
and this can help reduce our switches processor load
and improve your data transfer and throughput speeds.
This makes jumbo frames ideal
for high-bandwidth applications,
such as storage area networks, large file transfers,
video streaming,
and server-to-server communications
within a controlled environment.
Now, jumbo frames have many advantages,
but they can also lead
to network problems if you improperly configure them.
This occurs because not all network equipment
is going to support jumbo frames.
Mismatched configurations
between network devices can also lead to dropped packets
and further reduce your network performance.
Another issue with jumbo frames is the potential
for fragmentation to occur.
If a jumbo frame encounters a device
or network segment with a smaller MTU size,
the frame will need to be split up
or fragmented into smaller size frames.
This fragmentation can actually negate any of the benefits
of using a jumbo frame because it leads to increased latency
and processing overhead on your network devices.
Another major issue with jumbo frames
is that they make troubleshooting, diagnosing,
and fixing network issues much more challenging
because many of our traditional
network troubleshooting tools
do not support the larger frame sizes used by jumbo frames.
So to effectively use jumbo frames in your network,
you really need to ensure that all of your network devices,
including your switches, your routers,
and your network interface cards are all going to be able
to support the use of jumbo frames,
and they're all configured consistently
across all of your network devices
to use the same MTU size,
you also should monitor your network performance
and conduct thorough testing before
and after you implement jumbo frames
in your network to ensure that you're receiving
the intended benefits of using those jumbo frames.
Now, let's consider a real-world example
to better understand how MTU size
is going to be configured in our networks.
Let's assume that you're working on a medium-sized business
that has a mix of both wired
and wireless networks for use by its onsite employees,
but they also use a VPN for its remote employees
to use when they're on travel
or if they're working from home.
Now, the network administrator wants to configure
the wired ethernet segments to use the standard
or default MTU size of 1500 bytes on this network.
But for the wireless network, they're going to opt
for a slightly lower MTU size of around 1420 bytes
to accommodate the less stable nature
of our wireless networks.
For our VPN connections,
the MTU size is going to be reduced even further
by making the MTU size only 1400 bytes in size to account
for the additional overhead that's going to be introduced
by a VPN encapsulation process
as we send that data over the network.
On the other hand, this network can also serve a portion
of the organization's data center.
Inside of the data center,
the organization's servers are going to communicate extensively
with each other over a specialized high speed network.
So for that portion of the network,
the network administrator might decide
to implement jumbo frames
by setting the maximum MTU size at 9000 bytes
to optimize their data transfer efficiency
for these large file transfers between the servers.
So remember, when it comes to the maximum transmission unit,
or MTU size, what we're referring to is the largest size
of a data packet or frame that can be sent over the network.
This frame size is measured in bytes,
and the frame size will dictate how much data can be sent
and processed by a network
in a single transaction or transmission.
Our standard or default MTU size
for a wired ethernet network is going to be 1500 bytes,
and the standard or default MTU size
for a jumbo frame is going to be 9000 bytes in size.
If you're going to configure an MTU size for a wireless network
of VPN connection
or a PPPoE connection, then I recommend that you aim
for an MTU size of around 1400 to 1420 bytes in size
to give you the best performance for your networks.
By mastering the MTU configurations,
network administrators are going to significantly enhance
their network efficiency, stability,
and overall performance.