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In this lesson,

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we're going to cover the maximum transmission unit.

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The maximum transmission unit, or MTU,

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refers to the largest size of a frame

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that can be sent over a network.

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The frame size is measured in bytes,

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and the frame size dictates how much data can be sent

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and processed by a network

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inside of a single transaction or transmission.

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Personally, I like to think

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about the maximum transmission unit

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as the maximum load capacity

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for your frames inside of your network.

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For example, in the real world,

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you might walk into an elevator in a high rise building,

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and you can see a sign that says,

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"Maximum capacity, 10 people," or 2,500 pounds.

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And this is the equivalent

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of your maximum transmission unit size.

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If you try to put more than 10 people

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or more than 2,500 pounds in that elevator,

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it probably won't work, or,

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it would cause some kind of strange issues,

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just like if you try to put more data into a frame

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than it's designed to hold.

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Now, when we talk about a maximum transmission unit,

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it's really important that you realize

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that these MTUs will impact the performance

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and efficiency of your network.

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A properly configured MTU will ensure that the data packets

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and frames are neither too large or too small.

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If you set the MTU too high, then your packets

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and frames may be too large for the network to handle,

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and this can lead to packet loss

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and the need for data to be remitted.

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On the other hand, if you set the MTU too small,

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the network will experience increased overhead

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due to the larger number of packets that need to be sent,

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which can also slow down

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your network's maximum transmission data speed too.

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Now, the MTU size that you're going to configure

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is going to depend on the type of network

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and the type of traffic

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that you're trying to support.

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If you're using a wired ethernet network,

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the standard or default MTU size is 1500 bytes.

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This size is generally considered acceptable in the industry

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because it balances out the efficiency

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and compatibility requirements across many different types

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of network equipment and internet pathways

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without causing any issues.

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Now, if you're using a wireless network, though,

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you may need to use a smaller MTU size.

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The smaller size is often required

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because our wireless networks are inherently unstable

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and they have higher error rates during their communication.

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So using a larger MTU size could lead to larger packets

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with increased retransmission rates too,

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and that's why we like to use a smaller size

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when we're dealing with wireless networks.

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Now, if you're going to be using a virtual private network

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or a point-to-point protocol over ethernet connection,

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known as a PPPoE,

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you may need to configure your devices

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to use a smaller MTU size.

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This is because both the VPN

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and PPPoE connections will utilize an encapsulation process

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that add extra headers to the packets,

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and this reduces the remaining space available

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for the actual data payload inside of the frame.

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Personally, when I set up A VPN or a PPPoE connection,

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I tend to configure my MTU size

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to something between 1400 and 1450 bytes in size.

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Now, this leaves enough room

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for the additional overhead required

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when I'm forwarding the VPN or PPPoE frames

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out to the rest of my network.

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The final MTU configuration you need to be aware of

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is known as a jumbo frame.

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Now, a jumbo frame simply refers to any frame

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that exceeds the standard

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or default ethernet MTU size of 1500 bytes.

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While a jumbo frame can be any frame larger than 1500 bytes,

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generally, you're going to see that our jumbo frames

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are configured to use the default size

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of 9000 bytes instead.

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These larger 9000 byte frames are beneficial

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when working in storage area networks

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because they can enhance the efficiency

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of your data transfers by reducing your overhead.

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This occurs because more data is being sent inside

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of a single jumbo frame,

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and this can help reduce our switches processor load

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and improve your data transfer and throughput speeds.

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This makes jumbo frames ideal

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for high-bandwidth applications,

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such as storage area networks, large file transfers,

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video streaming,

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and server-to-server communications

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within a controlled environment.

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Now, jumbo frames have many advantages,

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but they can also lead

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to network problems if you improperly configure them.

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This occurs because not all network equipment

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is going to support jumbo frames.

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Mismatched configurations

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between network devices can also lead to dropped packets

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and further reduce your network performance.

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Another issue with jumbo frames is the potential

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for fragmentation to occur.

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If a jumbo frame encounters a device

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or network segment with a smaller MTU size,

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the frame will need to be split up

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or fragmented into smaller size frames.

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This fragmentation can actually negate any of the benefits

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of using a jumbo frame because it leads to increased latency

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and processing overhead on your network devices.

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Another major issue with jumbo frames

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is that they make troubleshooting, diagnosing,

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and fixing network issues much more challenging

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because many of our traditional

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network troubleshooting tools

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do not support the larger frame sizes used by jumbo frames.

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So to effectively use jumbo frames in your network,

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you really need to ensure that all of your network devices,

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including your switches, your routers,

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and your network interface cards are all going to be able

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to support the use of jumbo frames,

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and they're all configured consistently

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across all of your network devices

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to use the same MTU size,

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you also should monitor your network performance

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and conduct thorough testing before

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and after you implement jumbo frames

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in your network to ensure that you're receiving

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the intended benefits of using those jumbo frames.

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Now, let's consider a real-world example

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to better understand how MTU size

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is going to be configured in our networks.

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Let's assume that you're working on a medium-sized business

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that has a mix of both wired

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and wireless networks for use by its onsite employees,

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but they also use a VPN for its remote employees

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to use when they're on travel

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or if they're working from home.

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Now, the network administrator wants to configure

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the wired ethernet segments to use the standard

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or default MTU size of 1500 bytes on this network.

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But for the wireless network, they're going to opt

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for a slightly lower MTU size of around 1420 bytes

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to accommodate the less stable nature

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of our wireless networks.

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For our VPN connections,

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the MTU size is going to be reduced even further

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by making the MTU size only 1400 bytes in size to account

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for the additional overhead that's going to be introduced

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by a VPN encapsulation process

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as we send that data over the network.

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On the other hand, this network can also serve a portion

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of the organization's data center.

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Inside of the data center,

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the organization's servers are going to communicate extensively

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with each other over a specialized high speed network.

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So for that portion of the network,

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the network administrator might decide

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to implement jumbo frames

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by setting the maximum MTU size at 9000 bytes

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to optimize their data transfer efficiency

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for these large file transfers between the servers.

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So remember, when it comes to the maximum transmission unit,

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or MTU size, what we're referring to is the largest size

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of a data packet or frame that can be sent over the network.

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This frame size is measured in bytes,

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and the frame size will dictate how much data can be sent

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and processed by a network

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in a single transaction or transmission.

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Our standard or default MTU size

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for a wired ethernet network is going to be 1500 bytes,

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and the standard or default MTU size

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for a jumbo frame is going to be 9000 bytes in size.

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If you're going to configure an MTU size for a wireless network

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of VPN connection

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or a PPPoE connection, then I recommend that you aim

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for an MTU size of around 1400 to 1420 bytes in size

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to give you the best performance for your networks.

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By mastering the MTU configurations,

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network administrators are going to significantly enhance

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their network efficiency, stability,

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and overall performance.