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I just applied a bunch of recommended updates this morning (which seems to have upgraded the kernel to 3.8.0-32.47), and suddenly I cannot connect to the machine on port 80 (http) or 22 (ssh). Ping still works. In addition, my syslog and kern.log are filling up with messages like

Oct 22 10:43:27 mu kernel: [ 4041.036862] Inbound IN=eth0 OUT= MAC=6c:62:6d:c8:b0:d3:18:03:73:34:81:b8:08:00 SRC= DST= LEN=48 TOS=0x00 PREC=0x00 TTL=128 ID=17389 DF PROTO=TCP SPT=59502 DPT=80 WINDOW=8192 RES=0x00 SYN URGP=0 

I can connect to the web server locally, so this smells like a firewall issue to me. I've tried:

  • doing "reset firewall" from inside GUFW
  • doing "sudo ufw allow 80" and "sudo ufw allow 22" from the command line

and that is not working. So I went and looked at "sudo iptables -L", and I'm getting this, but I don't understand the output (I have hidden my employer's domain with "example.com")

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     tcp  --  ad1.example.com  anywhere             tcpflags:! FIN,SYN,RST,ACK/SYN
ACCEPT     udp  --  ad1.example.com  anywhere            
ACCEPT     tcp  --  ad2.example.com  anywhere             tcpflags:! FIN,SYN,RST,ACK/SYN
ACCEPT     udp  --  ad2.example.com  anywhere            
ACCEPT     tcp  --  ad3.example.com  anywhere             tcpflags:! FIN,SYN,RST,ACK/SYN
ACCEPT     udp  --  ad3.example.com  anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     icmp --  anywhere             anywhere             limit: avg 10/sec burst 5
DROP       all  --  anywhere        
DROP       all  --  anywhere        
DROP       all  --  base-address.mcast.net/8  anywhere            
DROP       all  --  anywhere             base-address.mcast.net/8 
DROP       all  --      anywhere            
DROP       all  --  anywhere                
DROP       all  --  anywhere             anywhere             state INVALID
LSI        all  -f  anywhere             anywhere             limit: avg 10/min burst 5
INBOUND    all  --  anywhere             anywhere            
LOG_FILTER  all  --  anywhere             anywhere            
LOG        all  --  anywhere             anywhere             LOG level info prefix "Unknown Input"
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http
ufw-before-logging-input  all  --  anywhere             anywhere            
ufw-before-input  all  --  anywhere             anywhere            
ufw-after-input  all  --  anywhere             anywhere            
ufw-after-logging-input  all  --  anywhere             anywhere            
ufw-reject-input  all  --  anywhere             anywhere            
ufw-track-input  all  --  anywhere             anywhere            
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:http

Any idea what I've done wrong? Or how to fix it? (I think I'm about to learn a lot about iptables.)


Unsurprisingly, other services on the machine (MySQL) are not responding either. nmap is telling me that the ports are open, tho

chris@mu:/var/log$ nmap

Starting Nmap 6.00 ( http://nmap.org ) at 2013-10-22 10:55 EDT
Nmap scan report for sentry (
Host is up (0.00030s latency).
Not shown: 993 closed ports
22/tcp   open  ssh
80/tcp   open  http
111/tcp  open  rpcbind
139/tcp  open  netbios-ssn
445/tcp  open  microsoft-ds
3306/tcp open  mysql
5666/tcp open  nrpe
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1 Answer 1

I finally found "sudo iptables -F" which erased all the firewall rules (it's a dev machine, so I don't really care), and now everything is accessible.

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