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Old 08-30-2012, 06:41 PM
Joe Zeff
 
Default Failure to acquire IP over DHCP

On 08/30/2012 11:27 AM, Mark Haney wrote:

On 08/30/2012 01:54 PM, Joe Zeff wrote:

On 08/30/2012 10:39 AM, Mark Haney wrote:

I may be a bit thick here, but I see no reference to the OP having any
relation to CERN minus the public IP subnet the DHCP client is
requesting an IP from.


It's not obvious, but a little checking will show that CERN owns
137.138.x.y.


That much I got, but that may just be a config error on the laptop
rather than an association with CERN. I mean, they are public DHCP
addresses. So unless he works for them, or what have you, that won't work.

I'm not flaming, I'm just trying to make a point that he may not be
involved with CERN, so why should that matter?




Why should it matter? Well, what's going to happen when he requests a
web page? Will it be routed to him? Not very likely, when he's using
an IP address assigned to CERN, is it?

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Old 08-30-2012, 06:59 PM
Suvayu Ali
 
Default Failure to acquire IP over DHCP

Hi Marko and others,

On Thu, Aug 30, 2012 at 06:24:58PM +0200, Marko Vojinovic wrote:
>
> Let me guess --- on other outlets you get a real IP, 137.138.*.*, right? And
> that works as expected?
>

Yes, exactly.

> > > >To add to this, when other laptops
> > > >connect to my wall outlet, they work properly.
>
> Is the MAC address of your laptop registered with the CERN admins?

Yes, my MAC address is registered with CERN[1].

> In plain english, your machine first asks the server 137.138.16.6 for an IP
> assignment (DHCPREQUEST). The server refuses (DHCPNAK). Then your machine asks
> which dhcp servers are out there (DHCPDISCOVER), and asks anyone for an IP
> assignment (DHCPREQUEST). Three servers respond: 137.138.16.6 and 137.138.17.6
> refuse (DHCPNAK), while 192.168.0.1 accepts (DHCPACK) and gives you an
> internal IP, which doesn't seem to be able to access the outside world.
>

I did ask for help, but apparently we ran into a dead end. However
later an admin got in touch with me personally, however it's night here
and he will probably continue tomorrow again.

> I am not sure if this is a misconfiguration or implemented on purpose, but the
> CERN admins need to figure out why both of the two 137.138 dhcp servers have
> refused to give you an IP. This is the problem on their end of the wall
> outlet. Your machine seems to be configured correctly and also behaves
> correctly.
>

As far as I know, I should get an external IP. So things like:

$ ssh user@<external IP>

works.

> The guys at CERN usually know what they are doing, so the best bet would be to
> ask them for help, they should certainly be able to fix this.
>

There is no doubt they definitely know what they are doing very well,
the "official procedure" however is painfully slow[2].


Footnotes:

[1] And yes, I do work at CERN.

[2] Today is the 3rd day since I reported my issue.


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Old 08-30-2012, 07:04 PM
Suvayu Ali
 
Default Failure to acquire IP over DHCP

On Thu, Aug 30, 2012 at 01:32:34PM -0400, Mark Haney wrote:
> On 08/30/2012 11:01 AM, Suvayu Ali wrote:
> >On Thu, Aug 30, 2012 at 10:43:59AM -0400, Mark Haney wrote:
>
> >>
> >>What is the IP subnet that DHCP hands out? Is it on a different subnet from
> >>192.168.0.x?
> >>
> >
> >My understanding of networks is next to nothing; by subnet do you mean
> >the netmask field as reported by ifconfig? If so I have quoted that
> >below:
> >
> >eth2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
> > inet 192.168.0.114 netmask 255.255.255.0 broadcast 192.168.0.255
>
> Well, the netmask is part of the subnet equation. Maybe I should have
> queried you on your level of network knowledge. My apologies for
> over-talking it.
>

No worries, this gave me some motivation to read up over the weekend.

> The subnet for the other devices IPs, is it different from 192.168.0.X your
> laptop is getting? Such as 172.16.0.x Or even 192.168.1.X (X being the part
> of the IP that identifies a specific device.
>

When connected to the network with DHCP working properly, my laptop
should receive an external IP. So things like this should work:

$ ssh user@<external IP>

I guess that means the answer to your question would be "a properly
connected device would be on a different subnet".

> Does that help clarify?
>

Indeed it did.

Thanks,

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Old 08-30-2012, 07:11 PM
Suvayu Ali
 
Default Failure to acquire IP over DHCP

On Thu, Aug 30, 2012 at 11:25:47AM -0500, Dale Dellutri wrote:
> On Thu, Aug 30, 2012 at 9:36 AM, Suvayu Ali <fatkasuvayu+linux@gmail.com> wrote:
> > Hi,
> >
> > I have a weird problem; at my office every time I try to connect to my
> > wall outlet, my laptop gets assigned an internal IP (192.168.0.114) and
> > I cannot access the internet. However everything works as expected when
> > I use any other wall outlets. To add to this, when other laptops
> > connect to my wall outlet, they work properly.
> >...
>
> I assume by "wall outlet" you mean an RJ45 port.
>
> I assume you're using Fedora. Which one? F16, F17?
>

Sorry, I should have mentioned; this is F17 with all updates applied as
of this morning.

> Could you post the output of two commands:
> # ip addr show
> # ip route show
>
> Do it for each of the two cases:
> 1. When you cannot access the internet (and you get the internal IP
> 192.168.0.114)
> 2. When you can access the internet (you say that everything works
> when you use
> any other wall outlet).
>

At the moment I can't provide that for both; for case (2), when
everything works on another outlet I get the following:

<http://pastebin.com/fF5eSp7n>

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Old 08-30-2012, 07:19 PM
Marko Vojinovic
 
Default Failure to acquire IP over DHCP

On Thursday, 30. August 2012. 14.27.48 Mark Haney wrote:
> On 08/30/2012 01:54 PM, Joe Zeff wrote:
> > On 08/30/2012 10:39 AM, Mark Haney wrote:
> >> I may be a bit thick here, but I see no reference to the OP having any
> >> relation to CERN minus the public IP subnet the DHCP client is
> >> requesting an IP from.
> >
> > It's not obvious, but a little checking will show that CERN owns
> > 137.138.x.y.
>
> That much I got, but that may just be a config error on the laptop
> rather than an association with CERN. I mean, they are public DHCP
> addresses. So unless he works for them, or what have you, that won't
> work.
>
> I'm not flaming, I'm just trying to make a point that he may not be
> involved with CERN, so why should that matter?

Suvayu Ali is a particle physicist at the NIKHEF National Institute for
Subatomic Physics in Amsterdam, Netherlands. He is working in a group for
Marcel Merk, collaborating on the LHCb detector experiments which are going on
now at the LHC collider in CERN. It is quite often that collaborators from
various institutions around the world come to CERN every now and then. So did
I several years back. :-)

Besides, when you happen to be on a random place in the world and do a
DHCPDISCOVER, you typically will not get an answer from 137.138 dhcp servers,
unless that random place is an office in CERN.

HTH, :-)
Marko


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Old 08-30-2012, 07:31 PM
Marko Vojinovic
 
Default Failure to acquire IP over DHCP

On Thursday, 30. August 2012. 11.43.46 Dave Ihnat wrote:
> Once, long ago--actually, on Thu, Aug 30, 2012 at 11:24:58AM CDT--Marko
Vojinovic (vvmarko@gmail.com) said:
> > which dhcp servers are out there (DHCPDISCOVER), and asks anyone for
> > an IP assignment (DHCPREQUEST). Three servers respond: 137.138.16.6
> > and 137.138.17.6 refuse (DHCPNAK), while 192.168.0.1 accepts (DHCPACK)
> > and gives you an internal IP, which doesn't seem to be able to access
> > the outside world. I am not sure if this is a misconfiguration or
> > implemented on purpose, ...
>
> I would bet dollars to donuts they don't intend for that RFC1918 address to
> be out there. It'd be extremely sloppy to have it on the same segment as
> the 137.138 addresses; it's more likely something they don't intend to run
> a DHCP server that's doing so anyway.

The first thing that comes to mind is that someone plugged in a small router
there (unofficially, without proper authorization and configuration), between the
"wall outlet" and the computer, and the router tries to be an "local" dhcp
server. The MAC of the router is not in the CERN database, so the official dhcp
servers refuse to cooperate, and neither the router nor the machine plugged
into it can have access to the rest of the Internet. But that's just a wild
guess... ;-)

> > The guys at CERN usually know what they are doing, ...
>
> You'd certainly hope so!

Sure they do, I collaborated with them on a couple of occasions. Besides, they
are one of the base developers of Scientific Linux (a RHEL clone used
throughout CERN and related academia), so I certainly wouldn't consider them
noobs or something... :-)

Best, :-)
Marko



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Old 08-30-2012, 07:37 PM
Joe Zeff
 
Default Failure to acquire IP over DHCP

On 08/30/2012 12:19 PM, Marko Vojinovic wrote:

Suvayu Ali is a particle physicist at the NIKHEF National Institute for
Subatomic Physics in Amsterdam, Netherlands. He is working in a group for
Marcel Merk, collaborating on the LHCb detector experiments which are going on
now at the LHC collider in CERN. It is quite often that collaborators from
various institutions around the world come to CERN every now and then. So did
I several years back. :-)



Thank you. I doubt that most of us were aware of that. And, it does
explain very nicely why he's not at all surprised to learn that his
public IP is owned by CERN.



Besides, when you happen to be on a random place in the world and do a
DHCPDISCOVER, you typically will not get an answer from 137.138 dhcp servers,
unless that random place is an office in CERN.


Not unless it's very, very badly misconfigured, that's for sure. Back
when I did tech support for an ISP, I'd occasionally run across a LAN
that wasn't originally intended to be connected to the Internet, and had
been set up with a random subnet, generally one that was actually
assigned to some company somewhere.[1] I always made sure to explain to
the callers that this might cause problems in the future, especially if
they actually needed to connect to the company in question, and
suggested that they have somebody local reconfigure things properly.


On an off-topic note, does anybody know for sure what would happen?
I've always assumed that the site would be unreachable, but I've never
had the nerve to set things up that way and find out.


[1]There was a time when many routers came with setup instructions that
said that if you're not connected to the Internet, it didn't matter what
IP range you used.

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Old 08-30-2012, 07:47 PM
Suvayu Ali
 
Default Failure to acquire IP over DHCP

On Thu, Aug 30, 2012 at 09:19:11PM +0200, Marko Vojinovic wrote:
> On Thursday, 30. August 2012. 14.27.48 Mark Haney wrote:
> > On 08/30/2012 01:54 PM, Joe Zeff wrote:
> > > On 08/30/2012 10:39 AM, Mark Haney wrote:
> > >> I may be a bit thick here, but I see no reference to the OP having any
> > >> relation to CERN minus the public IP subnet the DHCP client is
> > >> requesting an IP from.
> > >
> > > It's not obvious, but a little checking will show that CERN owns
> > > 137.138.x.y.
> >
> > That much I got, but that may just be a config error on the laptop
> > rather than an association with CERN. I mean, they are public DHCP
> > addresses. So unless he works for them, or what have you, that won't
> > work.
> >
> > I'm not flaming, I'm just trying to make a point that he may not be
> > involved with CERN, so why should that matter?
>
> Suvayu Ali is a particle physicist at the NIKHEF National Institute for
> Subatomic Physics in Amsterdam, Netherlands. He is working in a group for
> Marcel Merk, collaborating on the LHCb detector experiments which are going on
> now at the LHC collider in CERN. It is quite often that collaborators from
> various institutions around the world come to CERN every now and then. So did
> I several years back. :-)
>

All that information only a web search away . Yes, I am employed by
Nikhef, and I am based at CERN at the moment.

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Old 08-30-2012, 07:50 PM
Suvayu Ali
 
Default Failure to acquire IP over DHCP

On Thu, Aug 30, 2012 at 09:11:01PM +0200, Suvayu Ali wrote:
> On Thu, Aug 30, 2012 at 11:25:47AM -0500, Dale Dellutri wrote:
> > Could you post the output of two commands:
> > # ip addr show
> > # ip route show
> >
> > Do it for each of the two cases:
> > 1. When you cannot access the internet (and you get the internal IP
> > 192.168.0.114)
> > 2. When you can access the internet (you say that everything works
> > when you use
> > any other wall outlet).
> >
>
> At the moment I can't provide that for both; for case (2), when
> everything works on another outlet I get the following:
>
> <http://pastebin.com/fF5eSp7n>
>

This is the output for case (1), when it doesn't work:

<http://pastebin.com/DVZNuNkB>

--
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Old 08-30-2012, 08:19 PM
Dale Dellutri
 
Default Failure to acquire IP over DHCP

On Thu, Aug 30, 2012 at 2:50 PM, Suvayu Ali <fatkasuvayu+linux@gmail.com> wrote:
> On Thu, Aug 30, 2012 at 09:11:01PM +0200, Suvayu Ali wrote:
>> On Thu, Aug 30, 2012 at 11:25:47AM -0500, Dale Dellutri wrote:
>> > Could you post the output of two commands:
>> > # ip addr show
>> > # ip route show
>> >
>> > Do it for each of the two cases:
>> > 1. When you cannot access the internet (and you get the internal IP
>> > 192.168.0.114)
>> > 2. When you can access the internet (you say that everything works
>> > when you use
>> > any other wall outlet).
>> >
>>
>> At the moment I can't provide that for both; for case (2), when
>> everything works on another outlet I get the following:
>>
>> <http://pastebin.com/fF5eSp7n>
>>
>
> This is the output for case (1), when it doesn't work:
>
> <http://pastebin.com/DVZNuNkB>

These two pastebins show that the "wall outlet" that doesn't work (case 1)
is specialized to only allow access the 192.168.0.0/24 lan. It's probably
connected to a different switch (or different VLAN) than the ones that do
work (case 2).

There's no mystery unless you think that the network administrators
have made some kind of mistake. It looks like a policy decision.

--
Dale Dellutri
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