[ale] dhcpd to multiple vlans from one server

Jim Kinney jim.kinney at gmail.com
Thu Jan 22 22:17:56 EST 2015


Ouch.

Flatten the damn network and make it a huge subnet and make your life
easier.

Or better, all real DHCP is on a single /24 (or /20 or larger) and use
static dhcp for most everything else. 

http://www.newegg.com/Product/Product.aspx?Item=N82E16833114084
$180 for 4 ports. 

All it takes is a bit of failure to loosen the purse strings.

On Fri, 2015-01-23 at 03:04 +0000, Robert L. Harris wrote:
>   Yeah, don't have hardware like that.  I inherited this network and
> did not get any sty in the architecture.  If I get up to Chicago I'll
> be dropping into someone's cube with a bat.  They Mae no plans for dns
> our dhcp.  I'm working on scrounged hardware.
> 
>   Right now I'm using the hp 5920 switch they put in to provide dhcp
> with vlan pools but I see that becoming unmaintainable pretty quickly
> due to static assignments.
> 
> Robert
> 
> 
> On Thu, Jan 22, 2015, 19:58 Jim Kinney <jim.kinney at gmail.com> wrote:
>         On Fri, 2015-01-23 at 02:41 +0000, Robert L. Harris wrote:
>         > I have multiple projects/products, etc at work we are
>         breaking into
>         > separate broadcast domains ( currently 11, likely to be
>         closer to 20
>         > ).  I don't want a different dhcp server per subnet/vlan.  I
>         can put a
>         > trunk port to the dhcp server so if I can have dhcpd
>         answering on each
>         > vlan so I have centrally managed dhcp, that's ideal.  So
>         maybe I'm
>         > stuck doing the eth0.21, etc with an IP on each subnet and
>         one dhcp
>         > server.
>         
>         I think you can do it with a single, very high port count
>         machine.
>         virtual nics won't do it. So a big box with x5 4 port nics
>         with a line
>         to each head switch or a vlan'ed port will work. Each subnet
>         get's it's
>         own stanza in the config file.
>         >
>         >
>         >
>         >
>         >
>         > On Thu Jan 22 2015 at 7:30:43 PM Jim Kinney
>         <jkinney at jimkinney.us>
>         > wrote:
>         >         +1. All it takes is a physical connection to the
>         subnet.
>         >
>         >         Not sure why separate vlans get assigned to separate
>         subnets.
>         >         It doesn't provide a benefit. Vlans are for having
>         overlapping
>         >         IP space in the same physical LAN. Which is only
>         useful when a
>         >         LAN fills up a 10. Class A. Maybe its easier at the
>         >         switch/router management level with more than 100
>         subnets.
>         >         Mostly, I see it used as a job guarantee for a
>         network admin.
>         >
>         >
>         >         On January 22, 2015 9:15:39 PM EST, Michael Trausch
>         >         <mike at trausch.us> wrote:
>         >                 ISC dhcpd will hand an address out based on
>         the
>         >                 interface it came in on. If if eth0 has
>         203.0.113.1/25
>         >                 and eth1 has 203.0.113.129/25, and the DHCP
>         server is
>         >                 authoritative for those two subnetworks,
>         then when it
>         >                 receives a request on eth0 for an address it
>         will
>         >                 issue an address in 203.0.113.0/25; when it
>         receives a
>         >                 request on eth1 it will issue an address in
>         >                 203.0.113.128/25.
>         >
>         >                 Sent from my iPad
>         >
>         >                 On Jan 22, 2015, at 7:37 PM, "Robert L.
>         Harris"
>         >                 <robert.l.harris at gmail.com> wrote:
>         >
>         >
>         >                 > Ok, so if I have 2 subnets:
>         >                 >
>         >                 > 172.20.1/24 on vlan 21
>         >                 > 172.20.2/24 on vlan 22
>         >                 >
>         >                 >
>         >                 > If a host plugs into a port assigned to
>         vlan 22, how
>         >                 > do I make sure dhcpd gives out the right
>         address?
>         >                 > That's the part of the designation I'm
>         missing.
>         >                 >
>         >                 >
>         >                 > Robert
>         >                 >
>         >                 >
>         >                 >
>         >                 >
>         >                 > On Thu Ja n 22 2015 at 5:17:25 PM James
>         Sumners
>         >                 > <james.sumners at gmail.com> wrote:
>         >                 >         You just have to define the
>         subnets in the
>         >                 >         config and put each subnet's pool
>         within its
>         >                 >         respective block. No need for
>         aliased IPs.
>         >                 >
>         >                 >         On Thursday, January 22, 2015,
>         Robert L.
>         >                 >         Harris <robert.l.harris at gmail.com>
>         wrote:
>         >                 >
>         >                 >                 Anyone have a dhcpd
>         serving multiple
>         >                 >                 subnets to multiple vlans
>         from a
>         >                 >                 single server on a trunk
>         they can
>         >                 >                 share configs?  I don't
>         want to
>         >                 >                 spawn a bunch of servers
>         and if I
>         >                 >                 can do it with a single
>         interface
>         >                 >                 that would be ideal.  If I
>         have to
>         >                 >                 go with eth0.0, eth0.1,
>         etc that's a
>         >                 >                 good second choice.
>         >                 >
>         >                 >
>         >                 >                 Robert
>         >                 >
>         >                 >
>         >                 >
>         >                 >
>         >                 >         --
>         >                 >         James Sumners
>         >                 >         http://james.sumners.info/
>         (technical
>         >                 >         profile)
>         >                 >         http://jrfom.com/ (personal site)
>         >                 >         http://haplo.bandcamp.com/ (band
>         page)
>         >                 >
>         >                 >
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>         >         --
>         >         Jim Kinney
>         >         Linux Systems Analyst
>         >         Physicist/Brewer
>         >         http://jimkinney.us
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>         
>         --
>         James P. Kinney III
>         
>         Every time you stop a school, you will have to build a jail.
>         What you
>         gain at one end you lose at the other. It's like feeding a dog
>         on his
>         own tail. It won't fatten the dog.
>         - Speech 11/23/1900 Mark Twain
>         
>         http://heretothereideas.blogspot.com/
>         
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-- 
James P. Kinney III

Every time you stop a school, you will have to build a jail. What you
gain at one end you lose at the other. It's like feeding a dog on his
own tail. It won't fatten the dog.
- Speech 11/23/1900 Mark Twain

http://heretothereideas.blogspot.com/



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