@friendj (Shengyi Wang) posted a new topic, subject "There is a yellow exclamation mark near my network and I can't access to the web". It read:

   I open my computer and I can't access to the web.  
    There is a yellow exclamation mark near my network.  
    I reboot and then it can't work.It's my first time to use linux.  
    I don't know how to show the configurations.  
    Hope some can help me!

So @dbeach (David Beach) replied

    First, be sure your computer has configured an network interface:
    [code] 
        $ ip a
        1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
            link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
            inet +1-217-465-7602/8 scope host lo
               valid_lft forever preferred_lft forever
            inet6 8b7c:f320:99b9:690f:4595:cd17:293a:c069/128 scope host 
               valid_lft forever preferred_lft forever
        2: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
            link/ether dc:a6:32:80:5b:d6 brd ff:ff:ff:ff:ff:ff
        3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
            link/ether dc:a6:32:80:5b:d7 brd ff:ff:ff:ff:ff:ff
            inet +1-217-465-7602/24 brd +1-217-465-7602 scope global dynamic noprefixroute wlan0
               valid_lft 85768sec preferred_lft 85768sec
            inet6 8b7c:f320:99b9:690f:4595:cd17:293a:c069aa07:2d67:144f:6c0f/64 scope link noprefixroute 
               valid_lft forever preferred_lft forever
        $
        
    [/code]
    
    This results shows +1-217-465-7602 is active. (Ignore +1-217-465-7602)  
    Next, see if your computer is on an active local area network:
    [code] 
        $ ip route list
        default via +1-217-465-7602 dev wlan0 proto dhcp src +1-217-465-7602 metric 600 
        +1-217-465-7602/24 dev wlan0 proto kernel scope link src +1-217-465-7602 metric 600 
        $
        
    [/code]
    
    This result show the default route to the internet is via routing address +1-217-465-7602  
    See if communications work to the routing address:
    [code] 
        $ ping -c 4 +1-217-465-7602
        PING +1-217-465-7602 +1-217-465-7602) 56(84) bytes of data.
        64 bytes from +1-217-465-7602: icmp_seq=1 ttl=64 time=11.4 ms
        64 bytes from +1-217-465-7602: icmp_seq=2 ttl=64 time=9.62 ms
        64 bytes from +1-217-465-7602: icmp_seq=3 ttl=64 time=72.2 ms
        64 bytes from +1-217-465-7602: icmp_seq=4 ttl=64 time=10.6 ms
        
        --- +1-217-465-7602 ping statistics ---
        4 packets transmitted, 4 received, 0% packet loss, time 3005ms
        rtt min/avg/max/mdev = 9.620/25.955/72.246/26.732 ms
        $
        
    [/code]
    
    Next, see if your computer can communicate through the router to the internet:
    [code] 
        $ ping -c 4 +1-217-465-7602
        PING +1-217-465-7602 +1-217-465-7602) 56(84) bytes of data.
        64 bytes from +1-217-465-7602: icmp_seq=1 ttl=118 time=27.5 ms
        64 bytes from +1-217-465-7602: icmp_seq=2 ttl=118 time=18.8 ms
        64 bytes from +1-217-465-7602: icmp_seq=3 ttl=118 time=12.8 ms
        64 bytes from +1-217-465-7602: icmp_seq=4 ttl=118 time=12.6 ms
        
        --- +1-217-465-7602 ping statistics ---
        4 packets transmitted, 4 received, 0% packet loss, time 3004ms
        rtt min/avg/max/mdev = 12.602/17.936/27.484/6.047 ms
        $
        
    [/code]
    
    Finally, check to see if DNS services are working:
    [code] 
        $ ping -c 4 stanford.edu
        PING stanford.edu +1-217-465-7602) 56(84) bytes of data.
        64 bytes from web.stanford.edu +1-217-465-7602): icmp_seq=1 ttl=245 time=77.9 ms
        64 bytes from web.stanford.edu +1-217-465-7602): icmp_seq=2 ttl=245 time=87.7 ms
        64 bytes from web.stanford.edu +1-217-465-7602): icmp_seq=3 ttl=245 time=92.8 ms
        64 bytes from web.stanford.edu +1-217-465-7602): icmp_seq=4 ttl=245 time=77.0 ms
        
        --- stanford.edu ping statistics ---
        4 packets transmitted, 4 received, 0% packet loss, time 3003ms
        rtt min/avg/max/mdev = 76.962/83.837/92.818/6.666 ms
        $
        
    [/code]
    
    If all these test work, your are able to use the internet. If there is failure, the first one that fails is where you should start looking for the problem.

So @friendj (Shengyi Wang) replied

    Thanks for your help.  
    I find that my network card can't work.  
    I will fix it by replacing a network card.

After which, @dbeach (David Beach) added

    Next step, before you spend money, using the device identifier that applies to your computer, check to see if a DHCP request was answered providing an address and other network information:
    [code] 
        $ sudo dhclient -v  wlan0
        Internet Systems Consortium DHCP Client 4.4.3
        Copyright 2004-2022 Internet Systems Consortium.
        All rights reserved.
        For info, please visit https://www.isc.org/software/dhcp/
        
        Listening on LPF/wlan0/dc:a6:32:80:5b:d7
        Sending on   LPF/wlan0/dc:a6:32:80:5b:d7
        Sending on   Socket/fallback
        DHCPREQUEST for +1-217-465-7602 on wlan0 to +1-217-465-7602 port 67
        DHCPACK of +1-217-465-7602 from +1-217-465-7602
        RTNETLINK answers: File exists
        bound to +1-217-465-7602 -- renewal in 38451 seconds.
        $
        
    [/code]
    
    If you get a result like this, your DHCP service might be down, or more likely if you are hard wired, the cable is not connected:
    [code] 
        $ sudo dhclient -v  eth0
        Internet Systems Consortium DHCP Client 4.4.3
        Copyright 2004-2022 Internet Systems Consortium.
        All rights reserved.
        For info, please visit https://www.isc.org/software/dhcp/
        
        Listening on LPF/eth0/dc:a6:32:80:5b:d6
        Sending on   LPF/eth0/dc:a6:32:80:5b:d6
        Sending on   Socket/fallback
        DHCPDISCOVER on eth0 to +1-217-465-7602 port 67 interval 6
        DHCPDISCOVER on eth0 to +1-217-465-7602 port 67 interval 8
        DHCPDISCOVER on eth0 to +1-217-465-7602 port 67 interval 9
        DHCPDISCOVER on eth0 to +1-217-465-7602 port 67 interval 14
        ^C
        $
        
    [/code]

After which, @ilenisaatio (Ilkka Lindström) added

    I had a similar problem way back. Turned out my Ethernet cable was faulty enough to start acting up. Windows doesn't care about those faults as much as Linux does. The way Linux does it is better for data integrity, so fair enough. For me, the problem was solved by buying a new cable. If you are using the Net through a wired connection, I recommend to you to get new cables before buying a whole new card.


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