single dhcp server with multiple subnets

[Senko, Mike]

responses in line...

>-----Original Message-----
>From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Simon Hobson
>Sent: Wednesday, July 30, 2014 1:20 PM
>To: Users of ISC DHCP
>Subject: Re: single dhcp server with multiple subnets

>"Senko, Mike" <Mike.Senko at seattle.gov> wrote:

> If I can obtain a cisco switch, I will. I think they do vlans very 
> well...LOL


>Yes they do, and it's something I've had to get my head around lately. Make sure you get a "real" Cisco switch, not a "Linksys with a Cisco badge" >one with a "similar but annoyingly completely different" CLI. If it's just something for testing, you can get older units off eBay for next to nothing.

> The 10.1.6.2 address was on the router connected to the trunk port. I 
> want to remove the router and just use the switch and its Relay Agent Config.

>Not sure if that's just "poor phrasing" or if you are confused about the functions of the different elements.


I was thinking or perhaps assuming too much, the Relay Agent allowed the dhcp request packet flood pass to the configured dhcp server.
With the server directly connected to the switch, no further hops would be made. If the packet had to be transported to another switch, then the router would be needed to get it there.

>A DHCP relay agent doesn't do any routing. It simply receives packets on one interface, adds teh GI-Addr field, and then puts the modified packet >into the agents IP stack to be delivered to the server. There needs to be a route to the server - but that does not necessarily mean that the relay >agent is doing the routing.

I'll have to read the Option 82 pages  again. How it functions may also depend on Rugged Com's implementation too. That old phrase regarding standards, -" there's so many of them!"

>The router is responsible for taking packets from one interface and forwarding them to the appropriate interface to get closer to their >destination.

>Some switches include routing functions - then it gets confusing as you have to keep track in your mind whether you are configuring switching >(Layer 2) or routing (layer 3) functions.

I usually capitalize L-3 Vlans to help differentiate between L-2 and L-3.

>The TL;DR version :
>You *need* a router somewhere in the network otherwise packets cannot be routed between subnets, and the relay agent will not be able to >function.

What is interesting is the DHCP Relay Agent config parameter is on a layer 2 switch, hence my statement above about forwarding the packets to another inherent (to the switch) L-2 vlan. I was also getting confused as to how the addressing was manipulated. The router I have (also RuggedCom) also has the DHCP Relay Agent parameter so it become a bit confusing if both are needed or just one. I've tried it both ways without success so far, though it's tough if there are multiple problems and I believe that may be the case at the moment.

>I suspect from the config that your switch includes routing functions, given that it has IPs configured on multiple VLAN interfaces. Typically, on an >L2 only device, you only configure an IP on the management VLAN/interface.
Exactly my thoughts too when I started with this product. There are no routing protocols configurable and only one location for a gw addresses. I don't suppose configuring static routes to the internal (to the switch) Vlans would be of help? I'll try it.

Thank you Simon!

Mike





_______________________________________________
dhcp-users mailing list
dhcp-users at lists.isc.org
https://lists.isc.org/mailman/listinfo/dhcp-users