Error: Failed to synchronize cache for repo ‘fedora’

When executing DNF Update, you encountered the following problem:

[zhangz@zwfedora23 ~]$ sudo dnf update
[sudo] password for zhangz:
    Error: Failed to synchronize cache for repo 'fedora'
[zhangz@zwfedora23 ~]$

Later, it was found that the agent problem was set before:

  1 [main]
  2 gpgcheck=1
  3 installonly_limit=3
  4 clean_requirements_on_remove=True
  5
  6 #proxy=http://10.0.13.109:808
~
~
~
~
~
~
~
~
~
~
~
/etc/dnf/dnf.conf [TYPE=] [POS=0006,0001][100%] [LEN=6]
"/etc/dnf/dnf.conf" [readonly] 6L, 103C

Just comment out the proxy line above.
all the existing proxy line, because I need a proxy in the company, otherwise when I connect to the external network, direct dial-up Internet at home there is no proxy problem, the 10 network segment of the LAN address does not exist, so the use of DNF will prompt an error.