Context :

Aims : We present asteroseismological inferences on RX J2117.1+3412 , the hottest known pulsating PG1159 star .
Our results are based on full PG1159 evolutionary models recently presented by Miller Bertolami & Althaus ( 2006 ) .

Methods : We performed extensive computations of adiabatic g -mode pulsation periods on PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 M _ { \odot } .
PG1159 stellar models are extracted from the complete evolution of progenitor stars started from the ZAMS , through the thermally pulsing AGB and born-again phases to the domain of the PG1159 stars .
We constrained the stellar mass of RX J2117.1+3412 by comparing the observed period spacing with the asymptotic period spacing and with the average of the computed period spacings .
We also employed the individual observed periods to find a representative seismological model for RX J2117.1+3412 .

Results : We derive a stellar mass M _ { * } \sim 0.56 - 0.57 M _ { \odot } from the period spacing data alone .
In addition , we found a best-fit model representative for RX J2117.1+3412 with an effective temperature T _ { eff } = 163 400 K , a stellar mass M _ { * } = 0.565 M _ { \odot } , and a surface gravity \log g = 6.61 .
The derived stellar luminosity and radius are \log ( L _ { * } / L _ { \odot } ) = 3.36 and \log ( R _ { * } / R _ { \odot } ) = -1.23 , respectively , and the He-rich envelope thickness is M _ { env } = 0.02 M _ { \odot } .
We derive a seismic distance d \sim 452 pc and a linear size of the planetary nebula D _ { PN } \sim 1.72 pc .
These inferences seem to solve the discrepancy between the RX J2117.1+3412 evolutionary timescale and the size of the nebula .
All of the seismological tools we use concur to the conclusion that RX J2117.1+3412 must have a stellar mass M _ { * } \sim 0.565 M _ { \odot } , much in agreement with recent asteroseismology studies and in clear conflict with the predictions of spectroscopy plus evolutionary tracks .

Conclusions :