[Leaplist] polling the dhcp server for an ip

[roland cruse]

>
> > install a
> > vserver kernel and create at least one Virtual Private Server (VPS).
>
> sounds cool, although i've never heard of it. what makes it different
> from something like xen?


It is  does not emulate, it does its virtualization through seperation.
Using sophisticated chroot, "capabilities" in the kernel, seperation of
processes and other bits. All VPSs share the same kernel. You of course
limits you only to Linux VPNs. From the host box you can "cd" right into the
directory trees of the VPSs. The VPSs share memory. You do not give away a
chunk of memory like you do in Xen. Vserver is not as sophisticated a
technology as Xen.

> wondering if there is a way you can easily poll a dhcp server for a
> > free ip
> > address?
>
> it's possible- it involves putting the ethernet card in promiscuous
> mode, and creating layer-two packets by hand.
>
> normally the kernel sends layer-three packets (packets where the
> outermost layer of encapsulation is IP, where the source and
> destination of the packet are specified by IP address) to the
> ethernet card, and the card adds the layer-two header (the source and
> destination MAC addresses) before dumping the packet on the wire.
>
> most cards support letting the OS hand already-made layer-two packets
> to the card, in which case it just dumps that packet on the wire
> without any further processing. this allows you to set the "source
> MAC address" for packets leaving the machine. since a DHCP server
> differentiates between machines by the MAC address, this trick of
> explicitly setting the source MAC address is what allows a single
> machine to get multiple DHCP leases.


Very interesting and bit over my head. I am going to have to re-read this a
few times before I think I understand it. Thanks.

most virtualization systems use this in order to allow "child"
> sessions to obtain their own DHCP leases from a DHCP server. i don't
> know specifically that this is how "linux-vserver" works, but i would
> imagine this is the case.


I do could not say for sure. But when starting up a vserver VPS the host box
looks to a configuration file to get the ip address of the VPS before it
starts it. I think it does networking for the VPS by aliasing the nic. When
you "ifconfig" on the host you get regular eth* output along with a
eth*:name-of-vps() also.

however, knowing that devry's DHCP server is sometimes flaky and has
> been known to run out of addresses during a LEAP meeting, you may
> actually be better off with bruce's suggestion of putting an IPCOP
> between devry and your machine- this way the IPCOP will get one IP
> from devry, and then you can get as many IPs as you need from the IPCOP.


Great.

at one point i was thinking about building a machine running xen,
> putting IPCOP in one session, and having multiple "internal"
> sessions, all running on one physical machine... and here's the
> kicker: the IPCOP session would have physical access to the outside
> etherent, while the xen0 session would not. i actually had something
> close to this running at one point- the xen0 session was disconnected
> from the physical ethernet and only saw the shared bridge group as an
> interface, while session #1 was running iptables and doing NAT for
> xen0 and the other children. it wasn't IPCOP, but it was the same
> underlying technology that ipcop uses, so it was pretty close.


Cool. I think in xen you can give a guest domain control over a nic. Which
might have been part of your setup.

I remember on the xen site there is a page of xen deployments where people
showed how they used xen. One included an ipcop as a guest domain along with
other domains. I remember he had to do some special stuff because of how
ipcop had changed its kernel or something like that. I think your very
limited to what you can do with networking on a vserver though. If I
understand it right you can only do firewalling/nat on the vps host box.

I installed xen on a box at work. The xen guest was a staging server. We
disabled it because we needed the memory it was taking up. I will be
building a new development box with vserver. In this case vserver seems to
work best for us. It has been very handy building test vps using the clone
feature which uses rsync by the way.

and now that centos 5 is about to be released, and it will come with
> xen built into it (and in fact the OS installer will pre-install xen
> and set up centos as the xen0 session, right out of the box) i plan
> on doing some testing with that, and doing xen hosting for friends
> and clients. this is why i asked about the differences between "linux-
> vserver" and xen, because within the next month or so i plan to "buy
> into" some kind of virtualization for my own server.


Once I started looking into it there are quite a few out there.

Here is a link to "supposed vserver hosting sites":
http://linux-vserver.org/VServer_Hosting
Many are from out of the states and are not in english. A quick look at the
english ones showed them advertising vps hosting but not stating the
technology (vserver). At work our production web servers are hosted in a
vserver environment but the boxes are ours and there is no sharing.

I am looking to go in with a friend and get virtual server hosting we have
scouted out a few hosts. A recommended one has filled up and is not taking
orders untill they get more servers...They where running xen.
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