docs: Correct links

Change-Id: I6dab30bfbca034ff0071f6d49cd0e0fd6f713494
diff --git a/docs/source/parallel-simulations.rst b/docs/source/parallel-simulations.rst
index 6034d6e..0ff2049 100644
--- a/docs/source/parallel-simulations.rst
+++ b/docs/source/parallel-simulations.rst
@@ -4,7 +4,7 @@
 A way to speed up your simulations is to run them in parallel taking advantage of the power of
 all the processors and the memory availability of your machine. This can be done by using the
 Message Passing Interface (MPI) along with the distributed simulator class `provided by NS-3
-<http://www.nsnam.org/docs/models/html/distributed.html#mpi-for-distributed-simulation>`_.
+<https://www.nsnam.org/docs/models/html/distributed.html#mpi-for-distributed-simulation>`_.
 
 To make use of MPI, the network topology needs to be partitioned in a proper way, as the
 potential speedup will not be able to exceed the number of topology partitions. However, it
@@ -30,7 +30,7 @@
 will work with distributed simulation.
 
 For more information, you can take a look at the `NS-3 MPI documentation
-<http://www.nsnam.org/docs/models/html/distributed.html#mpi-for-distributed-simulation>`_.
+<https://www.nsnam.org/docs/models/html/distributed.html#mpi-for-distributed-simulation>`_.
 
 Compiling and running ndnSIM with MPI support
 ---------------------------------------------