I knew a tool like this had to exist, but I had never needed to look in the past.  While debugging a RA problem, I come upon the need to view IPv6 router advertisements.  How can one do this?  tcpdump?  Yeah, I guess that could work.  It’s almost like using a bulldozer when a wheelbarrow is all you need, though.  I could use ndpmon, I suppose, but that, too seems like overkill.
So, the search began. After about 10 seconds of google searching….. Success!  A tool, does in fact exist for viewing exactly that type of packet.
Enter radvdump.  It is part of the marvelous rtadvd project.  It also exists in MacPorts.

Sweet, now I can see my IPv6 router advertisements in a very simple manner.  The syntax is very straightforward, the command sudo /opt/local/sbin/radvdump will yield you pretty much everything you need to know about what is in your router advertisement:

#
# radvd configuration generated by radvdump 1.6
# based on Router Advertisement from fe80::20d:b9ff:fe18:8ca1
# received by interface en0
#

interface en0
{
AdvSendAdvert on;
# Note: {Min,Max}RtrAdvInterval cannot be obtained with radvdump
AdvManagedFlag off;
AdvOtherConfigFlag off;
AdvReachableTime 0;
AdvRetransTimer 0;
AdvCurHopLimit 64;
AdvDefaultLifetime 1800;
AdvHomeAgentFlag off;
AdvDefaultPreference medium;
AdvSourceLLAddress on;


prefix 2001:470:xxxx:xxx::/64
{
AdvValidLifetime 2592000;
AdvPreferredLifetime 604800;
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr off;
}; # End of prefix definition




prefix 2001:470:xxxx:xxx::/64
{
AdvValidLifetime 2592000;
AdvPreferredLifetime 604800;
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr off;
}; # End of prefix definition




}; # End of interface definition