I previously ACCEPTed all output traffic by default.  Recently changed the policy to DENY output by default, only opening ports needed for server/application functionality.When I tried to mount a drive this morning, there was a timeout (the destination server is up).  If I set the output policy to ACCEPT, I'm able to mount without issue.I've added the following rules to my firewall:Chain INPUT (policy DROP 166 packets, 49616 bytes) pkts bytes target     prot opt in     out     source               destination             0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp spt:137 state NEW,ESTABLISHED   628 48984 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp spt:137 state NEW,ESTABLISHED     0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp spt:138 state NEW,ESTABLISHED    32  7244 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp spt:138 state NEW,ESTABLISHED     0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp spt:139 state NEW,ESTABLISHED     0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp spt:139 state NEW,ESTABLISHEDChain OUTPUT (policy DROP 30 packets, 1800 bytes) pkts bytes target     prot opt in     out     source               destination             0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:137 state NEW,ESTABLISHED     0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:137 state NEW,ESTABLISHED     0     0 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:138 state NEW,ESTABLISHED     0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:138 state NEW,ESTABLISHED     3   180 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           tcp dpt:139 state NEW,ESTABLISHED     0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0           udp dpt:139 state NEW,ESTABLISHED By temporarily setting output to ACCEPT, I generated some INPUT traffic on ports  udp:137, udp:138.   I see some OUPUT traffic on tcp:139.The second I change default output to DENY, I get timeouts again.Here's the /etc/fstab line://example.com/shares/acoder   /mnt/acoder cifs    credentials=/etc/credfile,dom=example,uid=0,gid=0,file_mode=0600,dir_mode=0700  0 0   0   0In the example above, //example.com/shares/acoder is a Windows server.Here's the relevant portion of /etc/services# grep -i NETBIOS /etc/services netbios-ns      137/tcp                         # NETBIOS Name Servicenetbios-ns      137/udpnetbios-dgm     138/tcp                         # NETBIOS Datagram Servicenetbios-dgm     138/udpnetbios-ssn     139/tcp                         # NETBIOS session servicenetbios-ssn     139/udpWhat other port(s) need to be open for mounting with cifs?
mount times out with iptables --policy OUTPUT DROP
centos;mount;iptables;firewall;cifs
You also need port 445 and make sure that you also have incoming related/established traffic allowed.grep 445 /etc/servicesmicrosoft-ds    445/tcp             # Microsoft Naked CIFSmicrosoft-ds    445/udp