Troubleshoot Configuration Problems with Your MacBook Network
If your encountering problems with the network you've set up for your MacBook, check the hardware first; then look for problems in the network settings. When using TCP/IP on your network, look for these specific things: the TCP/IP configuration mode, IP address, subnet mask, and router IP address (if you’re using a router to connect to the Internet or other networks).
To check these settings, open System Preferences and click the Network icon to bring up the Network pane. Click the Ethernet entry in the list and then follow these steps:
Make sure that the Configure IPv4 pop-up menu is set to the appropriate option.
Using DHCP: Select the Using DHCP option only if you’re using a cable/DSL modem/router or other DHCP server. Otherwise, set this to Manually.
Manually: If the configuration is set to Manually, check the IP Address, DNS Servers, Router, and Subnet Mask fields to make sure that they’re correct. If you’re not sure whether your Subnet Mask field entry is correct, you can usually make it the same as other computers on the same network with you. Most times, the subnet mask is 255.255.255.0.
To check your Internet connectivity to the rest of the Internet, try pinging Apple.
This checks the router and DNS settings.
If you’re set up for DHCP and your TCP/IP settings remain blank, make sure that your DHCP server — which could be your cable/DSL modem/router — is turned on and working properly.