Why would ports 21/25/110/143 show as open?

fonestar1978

I have never had a ftp/smtp/pop3/imap service installed behind my router and have never used these ports for anything. I thought it may have had something to do with the fact I was using an advanced ip-services IOS on my 2611XM, so I uninstalled it and replaced with a standard ipbasek9 image and the ports are still open (scanned using nmap from outside on another network).

Also none of my SIP ports are showing as open, yet my remote ip softphone connects fine. Nmap has never lied to me! Any educated guesses? I did have SDM installed at one point.

Writing the CCNA tomorrow finally!

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Comments

Bl8ckr0uter

I think they are opened by default before you run auto secure.

Here is some good reading:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080120f48.shtml

mzinz

Your SIP phones connect fine because those connections are happening from IN to OUT.

It is likely (if your ACL's allow) that ALL outbound connections are permitted. This allows things like softphones to connect, just like it allows you to connect to web pages.

I'm not sure why those ports you listed are open INBOUND. Let's take a look at your router config?

fonestar1978

I will post it here in a bit, need to go have breakfast!

fonestar1978

mzinz wrote: »

Your SIP phones connect fine because those connections are happening from IN to OUT.

It is likely (if your ACL's allow) that ALL outbound connections are permitted. This allows things like softphones to connect, just like it allows you to connect to web pages.

I'm not sure why those ports you listed are open INBOUND. Let's take a look at your router config?

Been scratching my head about this one for awhile so I would appreciate some help!

:

Router1#sh run
Building configuration...

Current configuration : 16019 bytes
!
version 12.4
no service timestamps debug uptime
no service timestamps log uptime
service password-encryption
!
hostname R1
!
boot-start-marker
boot-end-marker
!
no logging buffered
no logging console
enable secret 5 XXXXXXXXXXXXXXXXXXXXX
!
aaa new-model
!
!
!
aaa session-id common
no network-clock-participate slot 1
no network-clock-participate wic 0
ip gratuitous-arps
ip cef
!
!
no ip dhcp use vrf connected
ip dhcp excluded-address xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
ip dhcp excluded-address xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx
!
ip dhcp pool DATA_POOL
network xxx.xxx.xxx.xxx 255.255.255.0
!
ip dhcp pool VOICE_POOL
network xxx.xxx.xxx.xxx 255.255.255.0
!
!
ip dhcp update dns
ip domain name fonestar.kicks-ass.net
ip name-server xxx.xxx.xxx.xxx
!
crypto pki trustpoint TP-self-signed-1175546438
enrollment selfsigned
subject-name cn=IOS-Self-Signed-Certificate-1175546438
revocation-check none
rsakeypair TP-self-signed-1175546438
!
!
crypto pki certificate chain TP-self-signed-1175546438
certificate self-signed 01
30820243 308201AC A0030201 02020101 300D0609 2A864886 F70D0101 04050030
31312F30 2D060355 04031326 494F532D 53656C66 2D536967 6E65642D 43657274
69666963 6174652D 31313735 35343634 3338301E 170D3032 30333133 30353334
35385A17 0D323030 31303130 30303030 305A3031 312F302D 06035504 03132649
4F532D53 656C662D 5369676E 65642D43 65727469 66696361 74652D31 31373535
34363433 3830819F 300D0609 2A864886 F70D0101 01050003 818D0030 81890281
8100B6EC 1F10EFBF 86982EE7 BE10611C 564D6027 B65FD8D1 61710A14
quit
username xxxxxx privilege 15 password 7 XXXXXXXXXXXXXXXXXX
!
!
ip tcp synwait-time 10
!
class-map match-all voice
match access-group 105
!
!
policy-map policy1
class voice
priority 96
class class-default
fair-queue
!
!
!
interface Tunnel0
description Hurrican Electric IPv6 Tunnel Broker
no ip address
ip mask-reply
ip directed-broadcast
tunnel source xxx.xxx.xxx.xxx
tunnel destination xxx.xxx.xxx.xxx
!
interface FastEthernet0/0
description WAN-OUTSIDE
ip address dhcp
no ip redirects
no ip unreachables
no ip proxy-arp
ip nat outside
duplex auto
speed auto
no cdp enable
no mop enabled
!
interface Serial0/0
no ip address
ip mask-reply
ip directed-broadcast
shutdown
!
interface FastEthernet0/1
no ip address
ip mask-reply
ip directed-broadcast
duplex auto
speed auto
!
interface FastEthernet0/1.100
encapsulation dot1Q 100
ip address xxx.xxx.xxx.xxx 255.255.255.0
no ip redirects
no ip unreachables
no ip proxy-arp
ip nat inside
no keepalive
!
interface FastEthernet0/1.200
encapsulation dot1Q 200
ip address xxx.xxx.xxx.xxx 255.255.255.0
ip mask-reply
ip directed-broadcast
ip nat inside
no keepalive
!
interface Dialer0
no ip address
ip mask-reply
ip directed-broadcast
!
ip default-network xxx.xxx.xxx.xxx
ip forward-protocol nd
!
no ip http server
no ip http secure-server
ip nat translation timeout 15000
ip nat inside source list 100 interface FastEthernet0/0 overload
ip nat inside source static tcp xxx.xxx.xxx.xxx 4445 interface FastEthernet0/0 4445
ip nat inside source static tcp xxx.xxx.xxx.xxx 1720 interface FastEthernet0/0 1720
ip nat inside source static tcp xxx.xxx.xxx.xxx 8080 interface FastEthernet0/0 8080
ip nat inside source static tcp xxx.xxx.xxx.xxx 5061 interface FastEthernet0/0 5061
ip nat inside source static tcp xxx.xxx.xxx.xxx 5060 interface FastEthernet0/0 5060
ip nat inside source static udp xxx.xxx.xxx.xxx 5060 interface FastEthernet0/0 5060
ip nat inside source static tcp xxx.xxx.xxx.xxx 5901 interface FastEthernet0/0 5901
ip nat inside source static tcp xxx.xxx.xxx.xxx 5900 interface FastEthernet0/0 5900
ip nat inside source static udp xxx.xxx.xxx.xxx 443 interface FastEthernet0/0 443
!
ip access-list extended DENY-PRIVATE-IP
deny ip 172.16.0.0 0.15.255.255 any
deny ip 192.168.0.0 0.0.255.255 any
deny ip 169.254.0.0 0.0.255.255 any
deny ip 127.0.0.0 0.255.255.255 any
deny tcp any any eq smtp
deny tcp any any eq pop3
deny tcp any any eq nntp
deny tcp any any eq 143
deny tcp any any eq www
deny tcp any any eq 443
permit tcp any any eq 5060
permit ip any any
permit tcp any any
permit udp any any
permit icmp any any
permit igmp any any
!
logging trap debugging
logging source-interface FastEthernet0/0
access-list 100 permit ip xxx.xxx.xxx.xxx 0.0.0.255 any
access-list 100 permit ip xxx.xxx.xxx.xxx 0.0.0.255 any
no cdp run
!
control-plane
!
banner login ^CAuthorized access only!
Disconnect IMMEDIATELY if you are not an authorized user!
^C
banner motd ^C
This is a private network, all access is logged! Authorized Access Only!^C
!
line con 0
privilege level 15
password 7XXXXXXXXXXXXXX
login authentication local_authen
transport output telnet
line aux 0
password 7 XXXXXXXXXXXXXX
login authentication local_authen
transport output telnet
line vty 0 4
privilege level 15
password 7 XXXXXXXXXXXXX
logging synchronous limit 50000
transport input ssh
!
!
end

mzinz

You have no access-lists applied to your interfaces, therefore all ports are completely open, both inbound and outbound.

In other words, your router is not blocking or filtering any traffic.

Typically, on your WAN interface, you will have an access list applied. This access list should only permit traffic that you would like to enter inbound. For instance, if you are hosting a web server, and end-users on the internet need to view your website, you would have an access-list like this:

ip access-list extended OUTSIDE_IN
permit tcp any host 1.1.1.1 eq 80
deny ip any any

That access-list will allow connections from "any" - meaning any IP address - to "host 1.1.1.1" - meaning the device who's IP address is 1.1.1.1. Only connections on TCP port 80 are allowed.
The line below signifies that all other connections are denied.

fonestar1978

mzinz wrote: »

You have no access-lists applied to your interfaces, therefore all ports are completely open, both inbound and outbound.

In other words, your router is not blocking or filtering any traffic.

I have tried with "ip access-group DENY-PRIVATE-IP in" on the ingress wan facing fa0/0 and it doesn't make a difference. In fact on that access-list I implicitly denied tcp ports 25, 110, 143.

Also, if this was so why not port 7 tcp, port 514?, port 30 tcp being open? I'm kind of thinking this is not it.

Forsaken_GA

Could you post the output nmap is giving you?

And have you tried telnetting to the ports that it says are open just to see if you get any kind of banner or response?

What I think is happening is that, since you're explicitly denying those ports in an access list, nmap is getting back an ICMP connection refused message, and assuming that the ports are open based on that.

Forsaken_GA

To backup what I'm saying, here's a simple example on Ubuntu -

root@forsaken-ubuntu:~# nmap 127.0.0.1

Starting Nmap 5.00 ( Nmap - Free Security Scanner For Network Exploration & Security Audits. ) at 2010-10-19 18:00 EDT
Interesting ports on localhost (127.0.0.1):
Not shown: 998 closed ports
PORT STATE SERVICE
25/tcp open smtp
631/tcp open ipp

Nmap done: 1 IP address (1 host up) scanned in 0.27 seconds
root@forsaken-ubuntu:~# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination

Chain FORWARD (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination
root@forsaken-ubuntu:~# iptables -I INPUT -p tcp --dport 110 -j DROP
root@forsaken-ubuntu:~# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
DROP tcp -- anywhere anywhere tcp dpt:pop3

Chain FORWARD (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination
root@forsaken-ubuntu:~# nmap 127.0.0.1

Starting Nmap 5.00 ( Nmap - Free Security Scanner For Network Exploration & Security Audits. ) at 2010-10-19 18:01 EDT
Interesting ports on localhost (127.0.0.1):
Not shown: 997 closed ports
PORT STATE SERVICE
25/tcp open smtp
110/tcp filtered pop3
631/tcp open ipp

Nmap done: 1 IP address (1 host up) scanned in 1.41 seconds
root@forsaken-ubuntu:~#

So in the first instance, I had no indication of pop3, nor am I running a pop3 server on this box, but simply adding a rule to deny all traffic to port 110 caused nmap to show it as filtered