# nslookup yahoo.co.jp
Server: 192.168.26.2
Address: 192.168.26.2#53
Non-authoritative answer:
Name: yahoo.co.jp
Address: 124.83.187.140
Name: yahoo.co.jp
Address: 203.216.243.240
# curl yahoo.co.jp
The document has moved here.
etc...
⇒ 失敗したら、DNS(nameserver) の設定を疑う
# vi /etc/resolv.conf
; generated by /sbin/dhclient-script
nameserver 192.168.80.1
search localdomain
===== ごみの削除 =====
# yum clean all
# yum update
それでもダメなら
# rm -rf /var/cache/yum
# yum check-update
# yum update