CentOS - Nov 2010 - yum update and iptables

I'm doing some testing in a lab which is isolated from the rest of my
network (DMZ). I'm doing both inbound and outbound filtering at the
firewall (CentOS +iptables).

What protocols, ports and destination IP addresses does yum use to
identify updates, and then actually go get them for installation?

Looking at yum.conf and wireshark data, yum appears to go to a central
site, look up the closest mirrors, then query the mirrors for the latest
updates.

Using wireshark it appears that http and tcp are used, but the addresses
are all over the place (many mirrors).

Is there a way to restrict the outbound traffic to a small number of
mirrors? In other words, can I force yum to only check certain sites?

If that is not so easy, I should be able to restrict the outbound
traffic to a small set of addresses (yes/no?).

DaveM

On Wed, Nov 17, 2010 at 7:36 AM, David McGuffey
<davidmcguffey at verizon.net> wrote:
>
> I'm doing some testing in a lab which is isolated from the rest of my
> network (DMZ). I'm doing both inbound and outbound filtering at the
> firewall (CentOS +iptables).
>
> What protocols, ports and destination IP addresses does yum use to
> identify updates, and then actually go get them for installation?
>
> Looking at yum.conf and wireshark data, yum appears to go to a central
> site, look up the closest mirrors, then query the mirrors for the latest
> updates.
>
> Using wireshark it appears that http and tcp are used, but the addresses
> are all over the place (many mirrors).
>
> Is there a way to restrict the outbound traffic to a small number of
> mirrors? In other words, can I force yum to only check certain sites?
>
> If that is not so easy, I should be able to restrict the outbound
> traffic to a small set of addresses (yes/no?).
You can comment out "mirrorlist" and uncomment "baseurl" and
set it to
your preferred mirror in the files in "/etc/yum.repos.d".