Re: Airport DHCP Problem
- From: J.J. O'Shea <try.not.to@xxxxxxxxxxx>
- Date: Fri, 29 Feb 2008 17:52:57 -0500
On Wed, 27 Feb 2008 16:10:42 -0500, rezwits wrote
(in article <2008022713104250073-nospam@nospamcom>):
I bought an airport extreme december 20th. I setup everything
correctly. I used DHCP from a cable modem
Have the cable modem deliver an IP to the APE; most cable modems deliver just
one IP, unless they have routers built in. My Zoom 5241, for example, picks
up the IP my ISP (Comcast) sends out and delivers that IP to my APE. (You can
see that IP in the NNTP-Posting-Host line of my posts...) My APE then runs
NAT, and sets up a private network using DHCP which allows all my machines to
use that single IP to connect to the Internet.
If the cable modem is set to deliver a private network using DHCP, it might
be a good idea to turn that off, lest you set up a Double NAT condition. This
can be a Bad Idea unless done right.
and connected 3 ethernet
connections a usb printer and a laptop.
30 days (Jan 19, 2008) later my airport reported a problem stating that
the DHCP number was invalid. It was reporting a 69.x.x.x number or
169.x.x.x number,
These numbers would be two distinctly different, and serious, problems. If
you're getting a 69.x.x.y number, where 'x' is a number 0 to 255 and 'y' is a
number 1 to 254, then you're getting actual live Internet-routable IPs on
your private network. One or more of those actual live Internet-routable
numbers may belong to someone who paid real live cash for it. He'll be
annoyed when he finds he can't use it, as only one person can use an IP on
the Internet at a time. He will find out who has his IP, and express his
annoyance to your ISP. Your ISP will express their annoyance to you by
removing your account.
A 169.254.x.y number is an APIPA number, an Automatic Private IP Address
number. That means that your machines were expecting to find a DHCP server
and couldn't find one, and self-assigned a number. APIPA was a Microsoft
idea, but was an actual good idea and so has become a standard. The typical
cure for APIPA numbers is to restart the DHCP server.
basically this ip number that sometimes comes up and
is recognizable as a PROBLEM.
Both numbers would be a problem. a 69.x.x.y number would be a _serious_
problem.
I disconnected the airport and connected a pc directly to the cable
modem and the internet came thru.
Sounds like you had an APIPA number.
I went to a few sites and things
worked. I connected the airport back to the cable modem and tried to
get the DHCP part of Airport Utility to get that number going
correctly. After failing at this I took the Airport Extreme back to
best buy and exchanged it for another one.
you didn't need to do that. What you should have done was:
1 turn _off_ both the modem and the router
2 turn _on_ the modem, wait for it to come up properly; usually there'll be a
LED labeled 'online' or 'ready' or 'cable' or something like that, it varies
with modem vendors, the Zoom has a 'online' light. This light has to be lit
up a solid green. Flashing green is bad. Flashing or solid amber is very bad.
No light at all is extremely bad.
3 Once the relevant light is solid green, and only once the relevant light is
solid green, turn the router on. Wait for it to come up properly. In the case
of an APE, wait for the one and only light on the front of the box to go from
flashing amber to solid amber to solid green.
4 once the APE is showing green, you can connect to the Internet.
I installed the new Airport Extreme, and things went alright just like
the 1st one. After a week though during the night the DHCP problem
happened again, but fixed itself during the night, and the Airport
Extreme reported the problem.
You have a DHCP problem. Connect direct to the router, set it to _not_ do
NAT. Then connect to the APE and set it to do NAT... and to have a DHCP lease
of your choice, but shorter than 30 days. My APE is set for 4 days.
Now on Feb 26, 2008. The same problem is back again with this 2nd
Airport Extreme. The DHCP number is bad. But this time I was prepared.
I have 3 different IP numbers that were leased that I took note of. So
with these numbers I went to the DHCP part of the Airport Utility, and
changed it to static ip and put one of those numbers in. After getting
that in I went to Safari and things worked.
This is not a Long Term Solution. I have to be able to changed the
Airport to DHCP from the cable modem and lease an ip number.
I can't fix this, does anyone know how to reset it hard enough? Or make
it so this DHCP problem won't come up again?
Launch AirPort Utility and see what your system settings are.
In particular, you need to set the following:
The Airport/Summery pane should show your basic info: base station name, base
station status (there should be a green dot here...), firmware version,
serial number, AirPort MAC ID, Ethernet MAC ID, wireless mode (this should be
'create a wireless network'), network name (this should be the same as the
base station name unless you _like_ complications), wireless security (WPA or
WPA2; WEP is useless), wireless clients (number of devices connecting by
wireless right then), connect using (how the machine running AirPort Utility
is connecting; typically that should be by Ethernet) and the IP address
handed out by your ISP.
The Airport/Base Station pane is where you can enter the base station name,
base station password (set it up in your keychain!), the time server, the
time zone, and whether your base station can be configured over the Internet
or not. (Allowing SNMP over the Internet is a very bad idea; someone else can
take control of your router and change settings at will.)
The Airport/Wireless pane shows what wireless mode you're in (you should be
in 'create wireless network'), the network name, whether you have other
wireless access points on the network, whether you're 802.11n compatible,
what channels you're using, your security settings, and your wireless
password and options. (Options include the ability to hide the SSID if you so
desire.)
The Airport/Access Control pane merely allows you to turn on the ability to
restrict only devices with known MAC addresses to access your net. This is a
serious pain, as you have to know the MAC addresses of all devices on the
net. It also doesn't do that much for security, as the 'good' addresses can
be detected, and MAC address spoofing is easily done. I know the MAC
addresses of the devices on my net, but haven't bothered to enable this, as
entering them all into the AirPort Utility is both too much like work and of
dubious value.
The Internet/Internet connection pane specifies all things internet: the
connection method (which should be 'Ethernet' as your APE is connected to the
modem by Ethernet), how IPv4 on your local net is configured (DHCP, unless
you like doing unnecessary work), the IP address given you by your ISP, the
subnet mask for that IP, the ISP's local gateway, the DNS servers you're
using, the domain name for those DNS servers (I use OpenDNS instead of
Comcast's DNS; YMMV), the DHCP client ID (which should be blank...), and how
you have the system set up, usually by automatic on the WAN port and sharing
a public IP address.
The Internet/DHCP pane specifies how your local net is set; there are three
types of private networks, which are not routable over the Internet except by
a router using NAT such as an APE. These are the Class A private net,
10.x.x.y, Apple usually sets the APEs to use that one; and the Class B
private nets, 172.16.x.y through 172.31.x.y; and the Class C private nets,
192.168.x.y. You _must_ use one of the private nets or you're looking for
trouble. I personally set my APE to use a Class C private net, but unless you
know what you're doing, leave this alone and use what Apple set. The DHCP
range, the start and end of the DHCP pool, the lease time, reserved
addresses, and much more are set here.
The Internet/NAT pane is used to turn on and set up NAT, which is the
protocol which allows you to use a single routable IP and hang a whole
private network behind it. 'Enable NAT Port Mapping Protocol' should be
checked. Everything else should be blank. Don't mess with this unless you
know what you're doing.
The Printers pane is where you configure USB printers you're sharing.
The Disks pane is where you configure USB disks you're sharing.
The Advanced pane contains stuff you shouldn't touch unless you know what
you're doing.
And, oh, yeah, just in case you don't know... _never_ set a device's IP to
end with either '0' or '255'. On Class C networks, the most common type, all
IPs of the nature x.x.x.0 are used to identify the network, and all of the
type x.x.x.255 are used to broadcast to the entire network. It's not quite as
simple for Class A and Class B networks, but if you know enough to be
configuring a Class A or a Class B, you know what to do already, and you know
when and where you can use trailing 0s or 255s...
Laters...
--
email to oshea dot j dot j at gmail dot com.
.
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