Switching

Hi All,

   I recently found out thanks to some of you in the forum that Junos does not support DHCP Server/Client or DHCP relay for any interface that lives in a VR other then the main inet.0 table.  This was shocking to me as its a HUGE limitition that I cant believe has not been addressed.

Anyway does anyone have any type of workaround they use for this.  Picture you use the EX as your core switch that terminates 10 + subnets in different VR's so putting a DHCP server in every single subnet would not be a feasible solution.

Is it possible to trunk a bunch of layer 2 vlans all the way to one DHCP server?  Like I have a trunk link go to a DHCP server in this way?

Thanks!

I believe DHCP relay does actually work in VRs on the EX switches....just for some reason, its configured completely counter to everything else in virtual routers (ie - being configured under the virtual router) it's actually defined in the forwarding-options config of the what I would call the main routing instance ---

routing-instances {
    FOO {
        instance-type virtual-router;
        interface vlan.10;
    }
}
forwarding-options {
    helpers {
        bootp {
            interface {
                vlan.1 {
                    server 10.10.10.75; /* default VR DHCP relay*/
                }
                vlan.10 {
                    server 20.20.20.20 routing-instance FOO; /* guest VR DHCP relay */
                }
            }
        }
    }
}

for whatever reason there are actually configuration options under [edit routing-instances FOO forwarding-options] to configure DHCP relay, it just doesn't (or didn't at least) work.  You have to do it as shown above.

Give that a go and report back if it works for you . . .

Good luck,

will

 I've been pondering the same potential need in the near future. As I break the network into VLANs and subnets, I'm going to need a means of issuing correct DHCP addresses to those various subnets. I had hoped at first that unique instances of the JUNOS DHCP server could be associated with the VLANs/subnets... but that doesn't seem to be possible.

 Out of curiosity - what would the DHCP server arrangement be that would exist behind your example configuration? One physical server with virtual interfaces of some sort? In other words, short of having a bunch of individual DHCP servers or one server (or a virtual server) with numerous interfaces... how does one approach this issue?

Thanks!

 - Aaron

In your case does server 20.20.20.20 live in a different VR or does it live in the same VR as the dhcp request is comming from?

Hey All just to clarify some points

When you specify the server the VR you specify is the VR where the server lives not where the request will come from.  If your DHCP relay is crossing VR's you will need to have a route that points from one VR to another.  If you are using EX switches this is tough because the only way (that I have seen) to import routes from one to the other is if it came from a Dynamic routing protocol ( I saw a KB about this somewhere).

Thanks !

Hi

Your configuration didn't worked for me.

here is one that i tested. see enclosed diagram.

root@EX4200R# show forwarding-options 
helpers {
    traceoptions {
        file helpers;
        level all;
        flag bootp;
    }
    bootp {
        inactive: server 10.34.8.3;
        interface {
            vlan.30;
            vlan.3405;
            vlan.3406;
            vlan.111 {
                server 192.168.111.2;
            }
            vlan.222 {
                server 192.168.222.2;
            }
        }
    }
}

root@EX4200R# show routing-instances 
multicast {
    instance-type virtual-router;
    interface vlan.222;
    inactive: interface vlan.2222;
}

I tested it also with activated interface vlan.2222 under routing-instances. 

There was no problem with vlan.111, but with client requesting from vlan 222, the best i can achieve was ex4200 replying to 111

I just wanted to have interfaces facing to clients in different routing instances (default and multicast) and interfaces facing dhcp server in the default routing-instance or also in multicast routing-instance.

you have to include the routing-instance parameter:

set forwarding-options helpers bootp interface vlan.222 server 192.168.222.2 routing-instance multicast

will

Thanks will

Good evening,

So, I am struggling here a little bit.  I am not sure if this post answers the question to my issue.  Maybe I am misunderstanding or it just doesn't answer my problem.  

Here's what I have.

I have a DHCP server living in a VRF called Bananas which is on vlan 10.  The DHCP servers IP address is 192.168.10.116.  

set routing-instances Bananas instance-type virtual-router
set routing-instances Bananas interface vlan.10

I have a device in another VRF called Chocolate which is on vlan 20.  It needs to get an IP address from the DHCP server in Bananas

set routing-instances Chocolate instance-type virtual-router
set routing-instances Chocolate interface vlan.20

I set up for forwarding options as such...

set forwarding-options helpers bootp interface vlan.20 server 192.168.10.116 routing-instance Bananas

If you hate the set commands, lemme know and I can post my from my 'show'

With this config, I am not getting DHCP.  I statcically assign an IP address on my host on VLAN 20 and I am able to ping my gateway, I can ping through my router that routes between my VRFs but.. no go on relay.  

Am I missing something?  What is the cause of this madness!?  

I have had issues like this in the past and have actually had ProServices assist us and it was articulated that there was an issue getting a DHCP relay to work through VRFs where the DHCP was not on the inet0 VRF.  They said that we would need to use a RIB group.  This will not be a solution for this client.  Now this was some time ago and I was hoping that some one out here in internetland would be able to help.  

Thank you so much.

Look forward to some replies.