WAN reachability issue

[mazichimdi]

I am having an issue with connectivity between two wan remote sites within our enterprise network.

Site A can reach site b. Site b cannot reach site a. There is however reachability ONLY when the traceroutes and pings are sourced from the inside leg/interface of the edge dmvpn router 

[Aref Alsouqi]

Is there any firewall in between the sites? also, when you issue the traceroute from site b to site a without specifying the source, where the traffic gets stuck?

[MHM Cisco World]

SiteA and SiteB are both spokes ?

MHM