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networking:mtu_test [2014/09/18 11:34]
gcooper 		networking:mtu_test [2025/03/10 12:14] (current)
gcooper
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 ====== MTU, Jumbo Frames and Packet Fragmentation ====== ====== MTU, Jumbo Frames and Packet Fragmentation ======
  
-:!: MTU issues can be caused by PPPoE.+:!: 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 cause Microsoft Exchange to not accept mail.
Line 7: Line 7:
 :!: MTU issues can interfere with SSH connections. :!: MTU issues can interfere with SSH connections.
  
-:!: MTU is the maximum packet size.+**MTU** (maximum transmission unit) is the maximum Ethernet frame size.
  
-:!: MSS is the maximum data bytes carried within a packet.+**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                                   ^ +^Connection   ^MTU     ^MSS      ^Note                                       ^ 
-|DSL (PPPoE) |1492    |1464     |PPPoE = 8 bytes, Breaks Exchange SMTP  | +|DSL (PPPoE)  |1492    |1464     |PPPoE = 8 bytes, Breaks Exchange SMTP      | 
-|Cable       |1500    |1472     |                                       |+|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 ===== ===== Linux =====
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 ===== Windows ===== ===== Windows =====
 +
 +https://support.microsoft.com/en-us/help/900926/recommended-tcp-ip-settings-for-wan-links-with-a-mtu-size-of-less-than
  
 <file> <file>
-ping -f -l 8792 <hostname or IP>+ping -n 1 -f -l 8792 <hostname or IP>
 </file> </file>
  
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 These are tools which will figure out the MTU across the path between the host and the target: 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>
  
networking/mtu_test.1411061667.txt.gz · Last modified: 2014/09/18 11:34 by gcooper

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