NFS compound failed for server foosrv: error 7 (RPC: Authentication error)

Question

I'm setting up an Ubuntu NFS server with a Solaris 10 client. The basic configuration looks okay to me, and it was also working for some time. I'm getting an "RPC: Authentication error" message on the client.

server

/etc/exports:

/export/opencsw-future 192.168.3.0/24(rw,nohide,insecure,no_subtree_check,async)
/export/opencsw-current 192.168.3.0/24(rw,nohide,insecure,no_subtree_check,async)

$ ls -ld /export/opencsw-current
drwxr-xr-x 7 maciej maciej 4096 2012-02-05 14:55 /export/opencsw-current

client

$ grep opencsw /etc/vfstab
foosrv:/opencsw-current - /export/opencsw-current nfs - yes -
$ sudo mount /export/opencsw-current
NFS compound failed for server foosrv: error 7 (RPC: Authentication error)
(...repeated...)
nfs mount: mount: /export/opencsw-current: Permission denied

My server host name resolves to both IPv4 and IPv6 addresses.

Solution

The problem was that the NFS client tried to mount via an IPv6 address, and the server did not have any IPv6 entries. The fix was to add my IPv6 subnet to /etc/exports on the NFS server:

/export/opencsw-current 192.168.3.0/24(rw,nohide,insecure,no_subtree_check,async) 2001:X:Y:Z::/64(rw,nohide,insecure,no_subtree_check,async)