  We consider Randall-Sundrum scenarios based on SU(2)_L x SU(2)_R and a
discrete parity exchanging L with R. The custodial and parity symmetries can be
used to make the tree level contribution to the T parameter and the anomalous
couplings of the bottom quark to the Z very small. We show that the resulting
quantum numbers typically induce a negative T parameter at one loop that,
together with the positive value of the S parameter, restrict considerably
these models. There are nevertheless regions of parameter space that
successfully reproduce the fit to electroweak precision observables with light
Kaluza-Klein excitations accessible at colliders. We consider models of
gauge-Higgs unification that implement the custodial and parity symmetries and
find that the EW data singles out a very well defined region in parameter
space. In this region one typically finds light gauge boson Kaluza-Klein
excitations as well as light SU(2)_L singlet, and sometimes also doublet,
fermionic states, that mix with the top quark, and may yield interesting
signatures at future colliders.
