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--- networking:mtu_test [2014/06/15 11:32]
gcooper
+++ networking:mtu_test [2025/03/10 12:14] (current)
gcooper
@@ Line 1: / Line 1: @@
 ====== MTU, Jumbo Frames and Packet Fragmentation ======
+:!: MTU issues can be caused by the extra overhead of PPPoE, VPNs, VLANs, MPLS, VPLS, etc.
+:!: MTU issues can cause Microsoft Exchange to not accept mail.
+:!: MTU issues can interfere with SSH connections.
+**MTU** (maximum transmission unit) is the maximum Ethernet frame size.
+**MSS** (maximum TCP segment size) is the maximum data bytes carried within a TCP packet. **1472** is fairly safe.  Less than that is problematic due to fragmentation.
+^Connection   ^MTU     ^MSS      ^Note                                       ^
+|DSL (PPPoE)  |1492    |1464     |PPPoE = 8 bytes, Breaks Exchange SMTP      |
+|Cable        |1500    |1472     |Should cause no issues with fragmentation  |
+|IPSec VPN    |1446    |1418     |Mikrotik, No effort at optimization        |
+|Jumbo Frames |9000    |8972     |Used for storage networks, Max throughput  |
+{{ :networking:mtu.png?direct&750 |MTU Chart}}
 ===== Linux =====
@@ Line 32: / Line 50: @@
 ===== Windows =====
+https://support.microsoft.com/en-us/help/900926/recommended-tcp-ip-settings-for-wan-links-with-a-mtu-size-of-less-than
 <file>
-ping -f -l 8792 <hostname or IP>
+ping -n 1 -f -l 8792 <hostname or IP>
 </file>
@@ Line 41: / Line 61: @@
 These are tools which will figure out the MTU across the path between the host and the target:
-  * For Windows
+==== For Windows ====
-    * ''mturoute''
-  * For *nix
+https://www.iea-software.com/products/mtupath/
-    * ''tracepath''
-    * ''traceroute --mtu''
+<file>
+mtupath hostname.yourdomain.tld
+</file>
+http://www.elifulkerson.com/projects/mturoute.php
+<file>
+mturoute <hostname or IP>
+mturoute -t <hostname or IP>
+</file>
+==== For *nix ====
+<file>
+tracepath <hostname or IP>
+traceroute --mtu <hostname or IP>
+</file>

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