使用Linux网关无法访问一些网站

我们有一个LAN,Linux Box用作Internet网关.
在这个网关上,我们安装了内联网邮件服务器(sendmail),fetchmail,代理和DNS.
租用线路连接到此网关,并在此框中配置静态IP.

对于theblast 10-15天,已经注意到一些网站根本没有工作.
如果我将此相同的连接和IP配置到独立的Windows PC,则可以毫无问题地访问所有这些网站.

我无法浏览一些网站而无法ping通,但我可以使用nslookup解析地址.

我的局域网配置如下：

使用ifconfig：

enp2s0: flags=4419<UP,BROADCAST,RUNNING,PROMISC,MULTICAST>  mtu 1500
        inet 192.168.1.41  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::52e5:49ff:fe1b:daa8  prefixlen 64  scopeid 0x20<link>
        ether 00:00:00:00:00:00  txqueuelen 1000  (Ethernet)
        RX packets 67331121  bytes 8458827280 (7.8 GiB)
        RX errors 0  dropped 2138  overruns 0  frame 0
        TX packets 66307928  bytes 58607952676 (54.5 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 1  collisions 0

enp4s1: flags=4163<UP,MULTICAST>  mtu 1500
        inet XX.XXX.XXXX.XX  netmask 255.0.0.0  broadcast 49.255.255.255
        ether 00:00:00:00:00:00  txqueuelen 1000  (Ethernet)
        RX packets 66015747  bytes 58276418282 (54.2 GiB)
        RX errors 0  dropped 100  overruns 0  frame 0
        TX packets 53457822  bytes 7049917031 (6.5 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

/etc/resolve.conf

nameserver 8.8.8.8
nameserver 192.168.1.41

iptables的

# Generated by iptables-save v1.4.21 on Fri Aug 12 10:18:54 2016
*filter
:INPUT ACCEPT [6409479:525988637]
:FORWARD ACCEPT [26036553:16397355271]
:OUTPUT ACCEPT [6914932:970229461]
-A INPUT -i eth0 -j LOG --log-prefix "BANDWIDTH_IN:" --log-level 7
-A FORWARD -o eth0 -j LOG --log-prefix "BANDWIDTH_OUT:" --log-level 7
-A FORWARD -i eth0 -j LOG --log-prefix "BANDWIDTH_IN:" --log-level 7
-A OUTPUT -o eth0 -j LOG --log-prefix "BANDWIDTH_OUT:" --log-level 7
COMMIT
# Completed on Fri Aug 12 10:18:54 2016
# Generated by iptables-save v1.4.21 on Fri Aug 12 10:18:54 2016
*nat
:PREROUTING ACCEPT [1480942:133895346]
:INPUT ACCEPT [179896:21387703]
:OUTPUT ACCEPT [82634:5613521]
:POSTROUTING ACCEPT [231368:13257122]
-A PREROUTING -d XX.XXX.XXX.XX/32 -p tcp -m tcp --dport 80 -j DNAT --to-destination 192.168.1.250
-A POSTROUTING -s 192.168.1.132/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.127/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.188/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.199/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.20/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.181/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.233/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.77/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.134/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.113/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.19/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.20/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.197/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.198/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.9/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.5/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.119/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.1/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.98/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.182/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.40/32 -p tcp -m tcp --dport 21 -j MASQUERADE
-A POSTROUTING -s 192.168.1.134/32 -p tcp -m tcp --dport 21 -j MASQUERADE
-A POSTROUTING -s 192.168.1.181/32 -p tcp -m tcp --dport 21 -j MASQUERADE
-A POSTROUTING -s 192.168.1.181/32 -p tcp -m tcp --dport 21 -j MASQUERADE
-A POSTROUTING -s 192.168.1.98/32 -p tcp -m tcp --dport 21 -j MASQUERADE
-A POSTROUTING -s 192.168.1.177/32 -p tcp -m tcp --dport 443 -j MASQUERADE
-A POSTROUTING -s 192.168.1.89/32 -p tcp -m tcp --dport 443 -j MASQUERADE
-A POSTROUTING -s 192.168.1.129/32 -p tcp -m tcp --dport 21 -j MASQUERADE
-A POSTROUTING -s 192.168.1.66/32 -j MASQUERADE
-A POSTROUTING -s 192.168.1.250/32 -j MASQUERADE
COMMIT
# Completed on Fri Aug 12 10:18:54 2016
# Generated by iptables-save v1.4.21 on Fri Aug 12 10:18:54 2016
*mangle
:PREROUTING ACCEPT [33387672:17017857834]
:INPUT ACCEPT [6409479:525988637]
:FORWARD ACCEPT [26036554:16397355355]
:OUTPUT ACCEPT [6914932:970229461]
:POSTROUTING ACCEPT [32955572:17367734827]
COMMIT
# Completed on Fri Aug 12 10:18:54 2016

我该如何找到阻止这些连接的内容？我还应该在Linux机器中查看什么？
有人可以提示解决这个问题吗？还有什么我应该在这里提一下吗？
提前致谢.

解决方法

enp4s1(WAN)接口上的网络掩码错误.

此系统已配置IP地址49.x.x.x和网络掩码255.0.0.0(前缀/ 8).但这不是您的ISP提供给您的网络掩码.

因此,您将无法访问几乎所有IP地址也以49开头的网站.

要解决此问题,请在网络配置中修复网络掩码或前缀声明.我希望正确的前缀可以在27,28或29附近,具体取决于ISP.