Re: [dhcwg] Query on DHCP client with multiple host

[Ryan Scripps <[e-mail]>]

(This is probably beginning to go outside the scope of
this discussion group, but...)

The details of a VLAN configuration can differ by
vendor.  Simply stated, each VLAN will need to have a
either a DHCP server of DHCP relay on it.  I am most
familiar with Cisco stuff and have typically seen a
router card added to a switch chassis. This router
card has "interfaces" (all in software) for
each network and can act as router between VLANs and
also as a DHCP relay (Cisco calls it a "helper
address").  A DHCP broadcast will not be carried
across VLANs in any implementation of VLANs that I
have seen.

I have heard of some (presumably very complex)
implementations where switch ports are shunted to a
default VLAN with a DHCP server on it.  When the DHCP
server assigns an address, the DHCP server kicks off a
script file which dynamically reconfigures the
client's switch port with the correct VLAN assignment.

Good luck,
Ryan Scripps

--- Bhaskar S <[e-mail]> wrote:
> Hi Ryan,
> 
> Thanks for the info.
> 
> I would like to seek more clarification on using
> DHCP along with VLAN. Here
> I mean to say that I have to use DHCP to allocate
IP
> addresses to each of
> the VLAN interfaces, assuming that DHCP server is
> connected to one of the
> VLAN interfaces. Is this possible?
> 
> It seemed difficult to me because the DHCP
> requesting IP address for an
> interface would be sent only on that interface?
> 
> Thanks in advance.
> 
> Regards,
> Bhaskar S.
> 
> Regardomg
> ----- Original Message -----
> From: "Ryan Scripps"
> To: "Bhaskar S"
> Sent: Thursday, September 05, 2002 8:33 AM
> Subject: Re: [dhcwg] Query on DHCP client with
> multiple host
> 
> 
> > My interpretation is that a DISCOVER must be
sent
> from
> > each interface since they could each be on a
> different
> > network.
> >
> > VLANs do not alter the functionality of
DHCP.  You
> > must ensure that each VLAN has a DHCP server
or
> relay
> > agent in it somewhere, however.  Clients on
one
> VLAN
> > typically must route to another VLAN,
therefore
> DHCP
> > DISCOVERs will not be carried across VLANs. 
Your
> > switches may allow a single port to trunk
VLANs to
> a
> > single host which could have interfaces for
all
> > available VLANs.
> >
> > Best of luck,
> > Ryan Scripps
> >
> > --- Bhaskar S wrote:
> > > Hi,
> > >
> > > The DHCP RFC says:
> > >
> > > "A client with multiple network
interfaces must
> use
> > > DHCP through each
> > > interface independently to obtain
configuration
> > > information parameters for
> > > these seperate interfaces."
> > >
> > > Does the above statement mean that
DISCOVER
> message
> > > for getting IP
> > > address for a particular interface
should be
> sent
> > > only on that interface or
> > > does it mean that the DISCOVER message
has to be
> > > sent on each of
> > > the interfaces available on the node ?
> > >
> > > Also I would like links which would
give how to
> > > configure DHCP in a VLAN
> > > environment.
> > >
> > > Thanks in advance.
> > >
> > > Regards,
> > > Bhaskar S.
> > >
> > >
> >
> >
> >
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