How TCP really works: MTU vs MSS

Wireshark TCP Deep Dive continues: You need to understand this - whats the difference between Maximum Transmission Unit (MTU) vs Maximum Segment Size (MSS).

// MENU //
00:00 ▶️ Coming Up
00:25 ▶️ Intro
00:32 ▶️ Chris introduction
00:47 ▶️ Topic: Maximum Segment Size (MSS)
01:27 ▶️ Explaining Maximum Transmission Unit (MTU)
08:42 ▶️ Interface layout
10:25 ▶️ David Bombal "War Story"
12:00 ▶️ Wireshark demo
13:26 ▶️ Increasing the MTU on your device for larger connections
16:27 ▶️ Difference between MTU and MSS
19:36 ▶️ Wireshark demo (cont'd)
24:58 ▶️ Using Path MTU Discovery
27:02 ▶️ Ping and Wireshark demo
33:32 ▶️ Cool trick for Mac system
35:08 ▶️ TCP/MSS Clamping
38:21 ▶️ Chris Greer "War Story"
51:09 ▶️ What happens if you can't capture a server
55:08 ▶️ MSS Adjustment commands
56:55 ▶️ Tunnel Path MTU Discovery
57:40 ▶️ Figuring out 1432
01:02:52 ▶️ Conclusion
01:04:48 ▶️ "Cool features" in Wireshark

// Wireshark PCAP files //

// VLAD SOCIAL //
Thanks Vladimir Gerasimov!

// GOOD READING //

// MY STUFF //

// David SOCIAL //

// Chris SOCIAL //

// SPONSORS //

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#wireshark #tcp #mtu

[EWCRC]

Yes, more content with Chris and Wireshark. The real world examples are great and really helps show the thought process for going through the capture. It is also great how you go back and forth and ask questions that we the viewer may ask.

[davidbombal]

// MENU //
00:00 ▶ Coming Up
00:25 ▶ Intro
00:32 ▶ Chris introduction
00:47 ▶ Topic: Maximum Segment Size (MSS)
01:27 ▶ Explaining Maximum Transmission Unit (MTU)
08:42 ▶ Interface layout
10:25 ▶ David Bombal "War Story"
12:00 ▶ Wireshark demo
13:26 ▶ Increasing the MTU on your device for larger connections
16:27 ▶ Difference between MTU and MSS
19:36 ▶ Wireshark demo (cont'd)
24:58 ▶ Using Path MTU Discovery
27:02 ▶ Ping and Wireshark demo
33:32 ▶ Cool trick for Mac system
35:08 ▶ TCP/MSS Clamping
38:21 ▶ Chris Greer "War Story"
51:09 ▶ What happens if you can't capture a server
55:08 ▶ MSS Adjustment commands
56:55 ▶ Tunnel Path MTU Discovery
57:40 ▶ Figuring out 1432
01:02:52 ▶ Conclusion
01:04:48 ▶ "Cool features" in Wireshark


// Wireshark PCAP files //

// GOOD READING //

// MY STUFF //

// David SOCIAL //

// Chris SOCIAL //


// VLAD SOCIAL //
Thanks Vladimir Gerasimov!

// SPONSORS //

Please note that links listed may be affiliate links and provide me with a small percentage/kickback should you use them to purchase any of the items listed or recommended. Thank you for supporting me and this channel!

[imnainggolanpm]

7:55 is very IMPORTANT reminder.
MTU is per hop, while MSS, since it is on TCP, it's end-to-end.

Networking people (me too) sometimes jump the gun that when they pinged next hop and able to get 1500 bytes MTU (do not fragments), immediately assume it is the same treatment along the hops throughout the network.

I remember dealing with MPLS backbone team and they assumed basically that same thing.

UNTIL we went P routers by P routers pinged each hop and identified there was an issue where somehow the MTU on that hop was dropped down to ~400 bytes.

Once the "expert" backbone team rerouted the traffic away from that backbone path, then the application can resume.

[brunomedeirosfraga]

Amazing job, guys ! We see a lot of information written on web but when we see a live demo it's much more interesting and captivating. I've recently found David and Chris's channels and can't stop watching. Keep doing wireshark analyses for network problems ! It's awesome !

[JaCkFlApPiNg]

David and Chris, you won't believe how many networking professionals have no understanding on MTU or MSS, so thank you so much for this!
Please more on TCP and ideally the next with some focus on TTL (You touched on it in this video "My TTL started at 64 and it's now 54, so I'm going through 10 Routers")
Great video, subscribed and liked and will check out Chris' Youtube channel

[ryanflint]

Great video! I had a client running a Cisco 1100 in their home office - everything was working perfectly except for Netflix and Disney+ which seemed very strange. After a fair bit of investigation the issue turned out to be the MSS. They were on a home internet plan using pppoe so had to use IP TCP ADJUST-MSS 1452 command to account for the 8 byte overhead of pppoe.

[rusnakhraj]

This was a great video. It reminded me and issue that I was dealing with around 2 years ago with Aruba APs. Our client has setup like this. One local WLAN aruba controller on site Spain and one redundant controller which was on remote site in Sweden. Clients reported issue with slow wifi. I found out that clients that are connected to APs which are connected to remote controller experience slowness. Other users connected to APs which used local wlan controller had no issue. So we started live troubleshooting and see that ping was ok but there was real slowness when opening web page or doing skype call (user was green but with packet loss). We started to manipulate ping request with more bytes and then packet loss appeared. Later I found out that APs has set "do not fragment" bit by default and we did calculation with wan team that packet is too big. So on our side we turn on preemption which will move APs to local WLC if it is online and WAN team did their config to divide packets to smaller size. This was really great issue and I enjoyed it :)

Btw. redundat remote wlc served for several small sites. Usually medium and big sites had 2 local WLCs but because of fact that some customer sites were too small they had setup with one local and one remote wlc.

[esesimon]

Wow. I'm indeed wowed. This is an impressive and exceptional delivery.
It's unbelievable to find this kind of quality content for free. I felt I was in a classroom. I would appreciate a deep dive on the entire TCP/IP and Ethernet header.
Thanks for putting this out.

[dwaynesudduth]

Anohter fantastic collaboration and learning time. And the 'War Story" shows a real-world example for us to dive into and understand. Thank you David and Chris!

[TomWhi]

Boys, this video was incredible! Chris, you did an amazing job of practically explaining this and David’s input was very helpful.

[techlearner]

27:02 ▶ Ping and Wireshark demo. This part made my day. Best ever explanation I found on this concept. Thanks to you both 👍👍

[sirsquirrel]

I love the way you both engaged us all. I have really struggled in and out to know mtu and mss in detail. Now, I’m all good and proud. Thanks for the video. Keep up the great work!

[adajatobi]

Thank you so much Chris and David. This video is a goldmine and I learnt a lot from it. Watching it over and over again, and it just keeps making more sense.

[WillKohut]

These videos answer the question: what if Robin Williams was a network engineering vlogger? In all seriousness though, great content; appreciate the clear and real-world explanations!

[nilmega]

Guys, this stuff is awesome. More videos, please, and continue this great work you guys are doing.

[jacobhenriksen]

Nothing better than waking up, grabbing a cup of coffee and watch David and Chris talk about networking for an hour. Absolute fantastic content!

[smanolito]

Brilliant video. thanks guys. An hour with you guys and I learnt more than when I spend a year with my manager.

[cyphodias]

1:06:37 Yes please let’s get into the weeds. Great content as always from you and Chris. Thanks so much. 👍

[mk-ornm]

you two are like ... superman meets batman, no fighting though, only starting Justice League right away. Thanks for a great video.

[saramaeks]

I love these interviews, thank you so much for what you do David :) your channel has really helped me learn and grow as a web developer!