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Elie_Richa_2324's avatar
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Nov 04, 2015

MTU Description



I am implementing an F5 BIG IP CGNAT to a customer and the MTU in the internal and external VLAN is configured as 1500. When a client is trying to open an IPSEC with L2TTP connection using HTTPS and it's MTU is configured locally above than 1390, the page is not opening.


I need to check please, that when putting 1500 on F5 vlan, that means that the packet is reassemble to be 1500? Or the F5 can handle a maximum packet size of 1500? So in my case the packet received from F5 is reassembled to be 1500? Or it should directly be forwarded to the external vlan as it is, with a restriction of max packet size 1500? (Please note that when using IPSEC a static NAT is used on the F5)


Should I increase or decrease the MTU on the VLAN?


Thank you the help!


Elie Richa


1 Reply

  • The MTU setting on the VLAN "Specifies the maximum transmission unit (MTU) for traffic on this VLAN. The default is 1500." Just means anything larger than that the packet will be fragmented.