[Dnsmasq-discuss] DHCP Relay, assign address from other vlan, with no dhcp listening on it

SpiderX spiderx at spiderx.dp.ua
Mon Sep 19 09:54:27 BST 2011

On Thu, Sep 15, 2011 at 8:59 PM, richardvoigt at gmail.com
<richardvoigt at gmail.com> wrote:
> On Thu, Sep 15, 2011 at 12:03 PM, SpiderX <spiderx at spiderx.dp.ua> wrote:
> > On Thu, Sep 15, 2011 at 7:44 PM, richardvoigt at gmail.com
> > <richardvoigt at gmail.com> wrote:
> >>>>> Or is your router not the same device where your dnsmasq is running on?
> >>>> Exactly.
> >>
> >> Have you considered running the dhcp relay agent on the router instead
> >> of the L2 switch?  This approach often offers much more flexibility
> >> and capability.
> >>
> > In this case I have to run it on every client's vlan(interface) on router,
> > that almost doesn't differ from running dhcp server on such vlans.
> > There are still lots of broadcast between router and client.
> > I still lose one ip per vlan.
> > Almost no benefits.
> How are you losing an IP address?  Doesn't the client need a default
> gateway anyway?
> If all these VLANs are bridged at the router, the router still has the
> ability to detect which VLAN tag the DHCP request carried when it
> arrived, and add the correct DHCP options when relaying.
Yes, you are right. I don't lose an ip address.
The scheme with dhcp relay agent on router is working, but the other
negative points remain:
— broadcast between client and the router, which in either case would
be to blocked on l2 switch;
— a lot of open ports on the server (port 67 in each vlane);
— more complicated firewall on router and acl on l2 switch;
And what in case router is l3 switch? It must support dhcp-option 5
too, and here we get the same problem that was with the dhcp relay
agent on l2 switch.
Dhcpmasq needs to support ip addresses allocation, based on circuit-id
and remote-id only, without dhcp-option 5.

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