Linux NFS挂载时失败，报错：mount.nfs: Connection timed out

今天在转码业务平台挂载中兴分布式存储时，出现了挂载失败：

linux-82ke:~ # mount -t nfs 192.168.202.60:/mnt/zxdfs/CM_South23/root/cccloud_tenant_id10001155 /mnt/D989/60/mnt/wfs10 -v
mount.nfs: timeout set for Wed Jul 30 15:39:52 2014
mount.nfs: trying text-based options 'vers=4,addr=192.168.202.60,clientaddr=192.168.199.4'
mount.nfs: mount(2): No such file or directory
mount.nfs: trying text-based options 'addr=192.168.202.60'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying 192.168.202.60 prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying 192.168.202.60 prog 100005 vers 3 prot UDP port 39325
mount.nfs: mount(2): Connection timed out
mount.nfs: trying text-based options 'vers=4,addr=192.168.202.60,clientaddr=192.168.199.4'
mount.nfs: mount(2): No such file or directory
mount.nfs: trying text-based options 'addr=192.168.202.60'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying 192.168.202.60 prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying 192.168.202.60 prog 100005 vers 3 prot UDP port 32954
mount.nfs: mount(2): Connection timed out
mount.nfs: trying text-based options 'vers=4,addr=192.168.202.60,clientaddr=192.168.199.4'
mount.nfs: mount(2): No such file or directory
mount.nfs: trying text-based options 'addr=192.168.202.60'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying 192.168.202.60 prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying 192.168.202.60 prog 100005 vers 3 prot UDP port 37809
mount.nfs: mount(2): Connection timed out
mount.nfs: Connection timed out

中兴分布式存储那边的/etc/exports配置为：
/data 192.168.199.*(rw,no_root_squash,sync,no_subtree_check)

但是奇怪的是，如果将/etc/exports修改为：
/data/test 192.168.199.4(rw,no_root_squash,sync,no_subtree_check)

挂载又是成功的。
最后无意间使用了如下配置后，居然正常了：
/data 192.168.199.0/24(rw,no_root_squash,sync,no_subtree_check)

又是一通郁闷……