This is server is behind a NAT, sure, but no proxies. I can download anything using wget without a problem! I have several systems/servers behind NAT; all are working fine.
More Details:
[root@asterisk ~]# yum clean metadata
Loaded plugins: aliases, allowdowngrade, changelog, downloadonly, filter-data, kernel-
: module, keys, kmod, list-data, merge-conf, priorities, protect-
: packages, protectbase, refresh-updatesd, security, tmprepo, tsflags,
: upgrade-helper, verify, versionlock
0 metadata files removed
0 sqlite files removed
0 metadata files removed
[root@asterisk ~]# yum update
Loaded plugins: aliases, allowdowngrade, changelog, downloadonly, filter-data, kernel-
: module, keys, kmod, list-data, merge-conf, priorities, protect-
: packages, protectbase, refresh-updatesd, security, tmprepo, tsflags,
: upgrade-helper, verify, versionlock
asterisk-current | 1.1 kB 00:00
asterisk-current/primary | 105 kB 00:00
asterisk-current 570/570
base | 3.7 kB 00:00
base/primary_db | 4.4 MB 00:01
http://vault.centos.org/6.5/os/x86_64/repodata/617a880b84a87969e04bfeebb1b96d5f441da42ee931d374fa6b6d57decd821e-primary.sqlite.bz2: [Errno -3] Error performing checksum
Trying other mirror.
base/primary_db | 4.4 MB 00:01
http://vault.centos.org/6.5/os/x86_64/repodata/617a880b84a87969e04bfeebb1b96d5f441da42ee931d374fa6b6d57decd821e-primary.sqlite.bz2: [Errno -3] Error performing checksum
Trying other mirror.
Error: failure: repodata/617a880b84a87969e04bfeebb1b96d5f441da42ee931d374fa6b6d57decd821e-primary.sqlite.bz2 from base: [Errno 256] No more mirrors to try.
[root@asterisk ~]#
And here is the only repo on the machine: FreePBX.repo
[root@asterisk ~]# cat /etc/yum.repos.d/FreePBX.repo
# FreePBX-Base.repo
#
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
#
[base]
#name=CentOS-6.5 - Base
name=CentOS-6.5 - Base
#mirrorlist=http://mirrorlist.freepbxdistro.org/?release=6.5&arch=$basearch&repo=os
#baseurl=http://yum.freepbxdistro.org/centos/6.5/os/$basearch/
#baseurl=http://yum.freepbxdistro.org/centos/6.8/os/$basearch/
#baseurl=http://vault.centos.org/6.8/os/$basearch/
baseurl=http://vault.centos.org/6.5/os/$basearch/
#mirrorlist=http://mirrorlist.freepbxdistro.org/?release=6.9&arch=$basearch&repo=os
gpgcheck=0
enabled=1
#released updates
[updates]
#name=CentOS-6.5 - Updates
name=CentOS-6.5 - Updates
#mirrorlist=http://mirrorlist.freepbxdistro.org/?release=6.5&arch=$basearch&repo=updates
#baseurl=http://yum.freepbxdistro.org/centos/6.5/updates/$basearch/
baseurl=http://vault.centos.org/6.5/updates/$basearch/
gpgcheck=0
enabled=1
#additional packages that may be useful
[extras]
name=CentOS-6.5 - Extras
#mirrorlist=http://mirrorlist.freepbxdistro.org/?release=6.5&arch=$basearch&repo=extras
baseurl=http://yum.freepbxdistro.org/centos/6.5/extras/$basearch/
gpgcheck=0
enabled=0
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-6.5 - Plus
mirrorlist=http://mirrorlist.freepbxdistro.org/?release=6.5&arch=$basearch&repo=centosplus
#baseurl=http://yum.freepbxdistro.org/centos/6.5/centosplus/$basearch/
baseurl=http://
gpgcheck=0
enabled=0
#Core PBX Packages
[pbx]
name=pbx
mirrorlist=http://mirrorlist.freepbxdistro.org/?pbxver=5.211.65&release=6.5&arch=$basearch&repo=pbx
#baseurl=http://yum.freepbxdistro.org/pbx/5.211.65/$basearch/
baseurl=http://vault.centos.org/5.11/os/$basearch
gpgcheck=0
enabled=1
#Schmooze Commercial Packages
[schmooze-commercial]
name=schmooze-commercial
mirrorlist= http://mirrorlist.schmoozecom.net/?release=6.5&arch=$basearch&repo=schmooze-commercial
#baseurl=http://yum.schmoozecom.net/schmooze-commercial/$release/$basearch/
gpgcheck=0
enabled=0
#High Availability Packages
[high-availability]
name=high-availability
#mirrorlist= http://mirrorlist.schmoozecom.net/?release=6.5&arch=$basearch&haver=r1&repo=high-availability
baseurl= http://yum.schmoozecom.net/high-availability/6/r1/$basearch/
gpgcheck=0
enabled=0