# Esp header size, payload size, and trailer size?



## jangli656 (Apr 3, 2011)

I need some help on ESP.
I want to calculate size of ESP header, its payload excluding ESP trailer, ESP trailer size, and AH size.
Is there a way to know that AH is used in the end of ESP or not? Please reply quick and with detail. Thanks.


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## DutchDaemon (Apr 3, 2011)

Why don't you just use Google? What is FreeBSD-specific about this?
http://www.networksorcery.com/enp/protocol/esp.htm
Wow, that took long.


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## jangli656 (Apr 4, 2011)

The point is I can't calculate esp payload. and how am I supposed to get my pointer to esp trailer when I don't know the size of esp payload?


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## DutchDaemon (Apr 4, 2011)

Again: what is specifically FreeBSD about this? Why wouldn't this be solved by following RFCs and other official protocol documentation?


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