TCP/IP stops working ... ?

Question

Level 1

19 points

TCP/IP stops working ... ?

All,

Searched for a bit here and didn't see a post discussing this issue, but if one does exist, please redirect me. Thanks.

I have a home network with the following:

- Airport Extreme WiFi
- iMac (10.6.x)
- MacBook Pro (10.6.x)
- MacBook Air (10.6.x)

All machines are connected using Wifi with the AE. This morning, the MBA complains that it cannot obtain an IP address via DHCP from the AE. I just get the little wireless icon with the exclamation point, and efforts to 'renew' from System Preferences --> Networking don't help. Other machines working just fine. I have attempted the following troubleshooting efforts, none of which help:

1. I have rebooted (MBA, other Macs, and the MBA) several times.

2. Assigning a manual IP address and DNS settings to the MBA. I have tried to ping other hosts on the network, but Terminal just gives me "you don't have permission" errors. Odd.

3. Turn off Wifi / Turn on Wifi, etc.

I also notice that AFP is working just fine and I can share iTunes libraries, etc. Just TCP/IP stopped working.

Anyone seen this before?

Bones

MacBook Air, Mac OS X (10.6.1), 2 GB RAM :: Purchasd circa Feb 2008

Posted on Oct 18, 2009 9:08 AM

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Answer 1

Oct 18, 2009 10:34 AM in response to _Bones_

Bones wrote:
I have a home network with the following:

- Airport Extreme WiFi
- iMac (10.6.x)
- MacBook Pro (10.6.x)
- MacBook Air (10.6.x)

All machines are connected using Wifi with the AE. This morning, the MBA complains that it cannot obtain an IP address via DHCP from the AE. I just get the little wireless icon with the exclamation point, and efforts to 'renew' from System Preferences --> Networking don't help. Other machines working just fine. I have attempted the following troubleshooting efforts, none of which help:

1. I have rebooted (MBA, other Macs, and the MBA) several times.

2. Assigning a manual IP address and DNS settings to the MBA. I have tried to ping other hosts on the network, but Terminal just gives me "you don't have permission" errors. Odd.

3. Turn off Wifi / Turn on Wifi, etc.

I also notice that AFP is working just fine and I can share iTunes libraries, etc. Just TCP/IP stopped working.

Anyone seen this before?

This thread

http://discussions.apple.com/message.jspa?messageID=10421726

has three suggestions for dealing with a similar problem, although they didn't seem to help that person. 😟

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Answer 2

_Bones_ Author

Level 1

19 points

Nov 4, 2009 11:47 PM in response to William-Boyd-Jr

Thanks for the link!

Just reviewed the options on the referenced thread. As predicted, none of them worked. I have looked at some other threads posted on external sites, and there seem to be some common issues:

1. This is only a problem between a Mac and an Apple Airport WiFi access point. Using a Linksys, Dlink, or other causes no problems.

2. The TTL value for TCP/IP packets being transmitted from the affected machine had been reduced. In my case, all machines on the network have a TTL=255, but the MacBookAir has a TTL=64.

I have found that assigning a manual IP address will in fact work, but you need to assign external IP addresses for DNS servers if you want to resolve host names and use a web browser. If you try to assign the default router, as most home networks do, it will fail.

Anyone know how to adjust the TTL value on a Mac?

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Answer 3

_Bones_ Author

Level 1

19 points

Nov 5, 2009 8:05 AM in response to _Bones_

OK.

Even further troubleshooting has revealed the anomaly causing this mess. Somewhere, somehow, OSX Snow Leopard on my MBA is "hard coded" to block access to the IP address 192.168.1.1.

Not exactly sure how this happened, or how to correct this issue, but comparing notes with others having the same issue, we all noticed that when we (1) cannot get an IP address from DHCP, and (2) cannot ping the default router (gateway), error below ...

ping 192.168.1.1
ping: sendto: Permission denied
ping: sendto: Permission denied
ping: sendto: Permission denied
ping: sendto: Permission denied
...

It had been on networks configured with RFC1918 address block 192.168.x.x and where the default router is set to be 192.168.1.1. On a whim, we all changed our internal addressing to another RFC1918 address block, 172.16.x.x, with a default router of 172.16.1.1, and all problems went away immediately.

Additionally, because I know someone will ask, we all had the OSX firewall turned off during the test. I know this is a bit more technical a question than the usual query on the Apple Discussions list support, but we would be grateful if someone could chime in.

_bones

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