NFS connection refused

Bad form, I know, to answer my own question, but.... I needed a couple more steps, outlined here. In short, I needed to execute:

sudo nfsd update

As another detail, I added the client name to the export and removed the "-rw" flag.

You can test some of this from the client side. rpcinfo is useful to tell you if rpc calls are making it to the server processes, then you can check mountd specifically, and lastly, showmount will ask the server what volumes are exported:

$ rpcinfo -p nfsserv103 | cut -c30- | sort -u
 mountd
 nfs
 nlockmgr
 portmapper
 rquotad
 status

$ rpcinfo -u nfsserv103 mountd
program 100005 version 1 ready and waiting
program 100005 version 2 ready and waiting
program 100005 version 3 ready and waiting

$ showmount -e nfsserv103 
Export list for nfsserv103:
/                     10.221.253.101,10.221.252.101,10.221.253.100,10.221.252.100
/mnt_foo/bar         (everyone)

(note that "cut" in the first command was just to make the output more concise. you can drop off everything but the first command.)