Cannot access the Internet

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Jun 22, 2009 5:11 PM
Jun 22nd, 2009

Resolution

These are possible resolutions to this problem:

  • It is possible that the internal devices do not have a default gateway or a more specific route to the destination. Verify that they have a route to the destination in their routing table or the default gateway is set. On a Cisco router you can verify that the default gateway is set by issuing the show ip route command.  This indicates if the gateway of last resort is set. By issuing the show ip route x.x.x.x command, where x.x.x.x is the destination address, you can verify if a route to the specific destination exists in the routing table.
  • If the default gateway or a route to the destination does exist, then it is possible that the Internet Service Provider is not advertising the appropriate network to the Internet. You must check with your ISP to verify this.
  • It is also possible that the reason that internal devices cannot access the Internet is due to an Access Control List (ACL) in the router blocking that device. Make sure you review the ACL's configuration in the router and you allow the devices you want to access the Internet.

Source

Multiple devices

Single device

What Can You Ping

Default gateway can ping destination

Source can ping ISP network but nothing beyond ISP

What Can You Not Ping

Source cannot ping anything beyond the Internet gateway router

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Posted June 22, 2009 at 5:11 PM
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