Cannot Access the Internet

Answered Question
Nov 26th, 2008

A computer with a IP Address 192.168.55.251 cannot access the Internet,but can see resources on the local (in house) network. why might this be?

It is a self assessment Interview question.

Thanks

I have this problem too.
0 votes
Correct Answer by wesleyterry about 8 years 6 days ago

Assuming the question is a troubleshooting and isn't as simple as the address is a private address, I'd say there is either a NAT problem to the internet or if it can't talk to ANY subnet other than its own, I'd go with the default gateway on the client being wrong...

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Joseph W. Doherty Wed, 11/26/2008 - 17:47

The simplest answer might be an 192.168.x.x address is a "private" address and isn't allowed on the Internet.

Joseph W. Doherty Thu, 11/27/2008 - 06:11

I see you marked Wesley's post as resolving your question. I just wanted to comment, Wesley's answer was excellent since he framed it within other conditions such as a troubleshooting a NAT issue or being unable to reach other internal subnets, but if the original self assessment question was as you posted, and incorrect gateway or NAT is the "correct" answer, it's a poor question and misleading.

For instance, when you stated "can see resources on the local (in house) network", and did not qualify this with but only those on the same subnet or VLAN, this might imply there isn't any gateway issue.

Certainly other issues can block access, such as John's post about ACLs, but since your original quesition was explicit about the host address, and it is "private" address (within the 192.168.x.x block), the correct answer should be its not valid on the Internet. Since it's not, you'll need to use a "public" address, which might be accomplished by NAT'ing the "private" address to a "public" address or moving to a public address for your host.

Again, the key point to such a question, I think, is the difference between private and public Internet addresses.

[edit]

If you're not aware:

Q. What are private IP addresses?

A. The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets (local networks):

10.0.0.0 - 10.255.255.255

172.16.0.0 - 172.31.255.255

192.168.0.0 - 192.168.255.255

Also, IP addresses in the range of 169.254.0.0 -169.254.255.255 are reserved for Automatic Private IP Addressing.

These IP's should not be used on the Internet.

Correct Answer
wesleyterry Wed, 11/26/2008 - 22:11

Assuming the question is a troubleshooting and isn't as simple as the address is a private address, I'd say there is either a NAT problem to the internet or if it can't talk to ANY subnet other than its own, I'd go with the default gateway on the client being wrong...

johnlloyd_13 Wed, 11/26/2008 - 23:31

there might be an ACL that's denying access to the internet, but another ACL line permits access to the local resources or LAN.

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