Why are some WAN ports listed as filtered in nmap?

Installing and Using OpenWrt Network and Wireless Configuration
1

I did a port scan from an external machine using nmap and noticed that some ports are listed as filtered, as opposed to closed.

Not shown: 995 closed ports
PORT    STATE    SERVICE
80/tcp  open     http
135/tcp filtered msrpc
139/tcp filtered netbios-ssn
443/tcp open     https
445/tcp filtered microsoft-ds

I have not configured any services for these ports so I'm wondering why they are not listed as closed. The router has been upgraded to 21.02 from 19.07 so there might be some old defaults but other than that I have not configured anything else than a couple of ports and a guest wifi.

Here is my /etc/config/firewall (with some disabled rules removed)

config redirect
	option target 'DNAT'
	option src 'wan'
	option dest 'lan'
	option proto 'tcp'
	option src_dport '80'
	option dest_port '80'
	option name 'HTTP'
	option dest_ip '192.168.77.243'

config redirect
	option target 'DNAT'
	option src 'wan'
	option dest 'lan'
	option proto 'tcp'
	option src_dport '443'
	option dest_port '443'
	option name 'HTTPS'
	option dest_ip '192.168.77.243'

config defaults
	option syn_flood '1'
	option input 'ACCEPT'
	option output 'ACCEPT'
	option forward 'REJECT'

config zone
	option name 'lan'
	list network 'lan'
	option input 'ACCEPT'
	option output 'ACCEPT'
	option forward 'ACCEPT'

config zone
	option name 'wan'
	list network 'wan'
	list network 'wan6'
	option input 'REJECT'
	option output 'ACCEPT'
	option forward 'REJECT'
	option masq '1'
	option mtu_fix '1'

config forwarding
	option src 'lan'
	option dest 'wan'

config rule
	option name 'Allow-DHCP-Renew'
	option src 'wan'
	option proto 'udp'
	option dest_port '68'
	option target 'ACCEPT'
	option family 'ipv4'

config rule
	option name 'Allow-Ping'
	option src 'wan'
	option proto 'icmp'
	option icmp_type 'echo-request'
	option family 'ipv4'
	option target 'ACCEPT'

config rule
	option name 'Allow-IGMP'
	option src 'wan'
	option proto 'igmp'
	option family 'ipv4'
	option target 'ACCEPT'

config rule
	option name 'Allow-DHCPv6'
	option src 'wan'
	option proto 'udp'
	option src_ip 'fc00::/6'
	option dest_ip 'fc00::/6'
	option dest_port '546'
	option family 'ipv6'
	option target 'ACCEPT'

config rule
	option name 'Allow-MLD'
	option src 'wan'
	option proto 'icmp'
	option src_ip 'fe80::/10'
	list icmp_type '130/0'
	list icmp_type '131/0'
	list icmp_type '132/0'
	list icmp_type '143/0'
	option family 'ipv6'
	option target 'ACCEPT'

config rule
	option name 'Allow-ICMPv6-Input'
	option src 'wan'
	option proto 'icmp'
	list icmp_type 'echo-request'
	list icmp_type 'echo-reply'
	list icmp_type 'destination-unreachable'
	list icmp_type 'packet-too-big'
	list icmp_type 'time-exceeded'
	list icmp_type 'bad-header'
	list icmp_type 'unknown-header-type'
	list icmp_type 'router-solicitation'
	list icmp_type 'neighbour-solicitation'
	list icmp_type 'router-advertisement'
	list icmp_type 'neighbour-advertisement'
	option limit '1000/sec'
	option family 'ipv6'
	option target 'ACCEPT'

config rule
	option name 'Allow-ICMPv6-Forward'
	option src 'wan'
	option dest '*'
	option proto 'icmp'
	list icmp_type 'echo-request'
	list icmp_type 'echo-reply'
	list icmp_type 'destination-unreachable'
	list icmp_type 'packet-too-big'
	list icmp_type 'time-exceeded'
	list icmp_type 'bad-header'
	list icmp_type 'unknown-header-type'
	option limit '1000/sec'
	option family 'ipv6'
	option target 'ACCEPT'

config rule
	option name 'Allow-IPSec-ESP'
	option src 'wan'
	option dest 'lan'
	option proto 'esp'
	option target 'ACCEPT'

config rule
	option name 'Allow-ISAKMP'
	option src 'wan'
	option dest 'lan'
	option dest_port '500'
	option proto 'udp'
	option target 'ACCEPT'

config include
	option path '/etc/firewall.user'

config zone
	option network 'guest'
	option forward 'REJECT'
	option name 'guest'
	option output 'ACCEPT'
	option input 'REJECT'

config forwarding
	option dest 'wan'
	option src 'guest'

config rule
	option dest_port '53'
	option src 'guest'
	option name 'Guest DNS'
	option target 'ACCEPT'

config rule
	option dest_port '67'
	option src 'guest'
	option name 'Guest DHCP'
	option target 'ACCEPT'
2

It's probably been done at the ISP level. It's not unusual for those ports to get blocked.

3 Likes
3

Thanks, that would make sense.

4

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