[CentOS] httpd listening only on IPv6 interface on CentOS 7

[Gordon Messmer]

On 12/11/2014 09:35 AM, Warren Young wrote:
>> Am 11.12.2014 um 04:48 schrieb Warren Young:
>>> the stock configuration of Apache only listens for IPv6 connections:

As per RFC 3493 (Sections 3.7 and 5.3) an IPv6 socket will accept 
connections from IPv4 hosts, which will be mapped into the IPv6 address 
space.

> We noticed this problem when web browsers would refuse to connect to the server.  *Then* we discovered the netstat oddity, and *then* we found that changing the Listen line in httpd.conf fixed it.
>
> That leaves me still wanting an explanation for what happened.
>
> New guess: there’s a difference between the IPv4 and v6 firewalls, so that changing the Listen line caused Apache to avoid the problem on the v6 side.

I don't have a good guess, there.  If the client was actually connecting 
from an IPv4 address, then the IPv4 firewall rules should have applied.  
At least, that's what my testing indicates.

What I can say for sure is that a CentOS 7 system will accept IPv4 http 
connections if the IPv4 firewall allows that port, or if the firewall is 
disabled.  Whatever problem you faced was caused by post-install 
configuration.  Try making your standard changes incrementally and 
testing as you go until you can locate the steps where the problem occurs.