Switching

Hello everyone,

I'm trying to set up a dhcp relay on one of my EX3300-24T.

I saw that the command was added to all EX switches in JunOS 12.1 and my switch is running JunOS 12.3.

See the addition in the changelog ('Infrastructure' section): http://www.juniper.net/techpubs/en_US/junos12.1/information-products/topic-collections/release-notes/12.1/index.html?topic-64014.html

I'm following this configuration guide:

https://www.juniper.net/techpubs/en_US/junos13.2/topics/task/configuration/dhcp-extended-relay-server-cli.html

First, i had trouble finding the dhcp-relay configuration as auto completion (through the '?' character) didn't suggest it. When i tried to type it in entirely it was accepted and i could start editing the dhcp-relay parameters. However, when i displayed the config it said that the whole block would be ignored as my switch doesn't support dhcp-relay. I must admit that i'm a bit surprised as it was stated that the functionality was added to every EX switch in JunOS 12.1.

This is what i get in my config:

forwarding-options {
    ##
    ## Warning: configuration block ignored: unsupported platform (ex3300-24t)
    ##
    dhcp-relay {
        server-group {
            dhcp-pool {
                192.168.6.19;
            }
        }
        active-server-group dhcp-pool;
        group dhcp-clients {
            interface vlan.1305;
        }
    }
}

Anyone experiencing the same bahavior ?

Is that normal?

How should I set up DHCP relay if that doesn't work?

Thanks for the input.

It seems like you are using the extended options, which by the looks of it seems to be supported with 13.2. Try this hierarchy

set forwarding-options helpers bootp

http://www.juniper.net/techpubs/software/junos-es/junos-es93/junos-es-admin-guide/configuring-the-device-as-a-bootpdhcp-relay-agent.html

Okay, so I ended up with this configuration block:

helpers {
    bootp {
        relay-agent-option;
        description "DHCP Relay";
        server 192.168.6.19;
        maximum-hop-count 10;
        minimum-wait-time 0;
        client-response-ttl 20;
        interface {
            vlan.1305;
        }
    }
}

I followed the guide suggested by Lyndidon but kind of sticked with the defaults. I assumed that:

• server is the DHCP server that should get the requests in the end.
• interface are the network interfaces from which DHCP requests can come from and should be forwarded to the server.
• minimum-wait-time is the time the relay waits before forwarding the DHCP request to the targeted server, thus i set it fairly low to prevent unnecessary wait (i suppose this can be used to prevent spamming the server with DHCP requests right?).
• maximum-hop-count and client-response-ttl seem to be quite the same to me so if anyone can provide some input on those, that'd be wonderful.

I've not tryed the config in production yet (as the DHCP clients are not yet plugged in in the network) i'll post back if it doesn't work 🙂

 Thanks for the help anyway!

EDIT:

Okay, so i looked around in Juniper's documentation and i found out that you can select the JunOS version for a guide. The guide I mentioned earlier about the extended relay server is also available for JunOS 12.3 (and 12.1 by the way). I come to the conclusion that what I wrote earlier should definitely be working on my switch. I really don't get it...

https://www.juniper.net/techpubs/en_US/junos12.3/topics/task/configuration/dhcp-extended-relay-server-cli.html

Here are the software versions of the switch:

root@xxxxx> show version                                     
fpc0:
--------------------------------------------------------------------------
Hostname: xxxxx
Model: ex3300-24t
JUNOS Base OS boot [12.3R3.4]
JUNOS Base OS Software Suite [12.3R3.4]
JUNOS Kernel Software Suite [12.3R3.4]
JUNOS Crypto Software Suite [12.3R3.4]
JUNOS Online Documentation [12.3R3.4]
JUNOS Enterprise Software Suite [12.3R3.4]
JUNOS Packet Forwarding Engine Enterprise Software Suite [12.3R3.4]
JUNOS Routing Software Suite [12.3R3.4]
JUNOS Web Management [12.3R3.4]
JUNOS FIPS mode utilities [12.3R3.4]

Do let us know how it works out.

Here is a link with a little better explanation for maximum-hop-count and client-response-ttl

maximum-hop-count - num of hops to forward bootp messages to DHCP server

client-response-ttl - IP time-to-live (TTL) value for DHCP response packets sent to a DHCP client

http://www.juniper.net/techpubs/en_US/junos13.2/topics/task/configuration/dhcp-and-bootp-relay-agents-qfx-series3.html

If you are able to do this, you can test in the after hours. enter the configuration then save it so you can apply it later permanently. Plug up a client, before you commit the configuration, then use #commit confirmed 10 (this will temporarily commit the configuration for 10 minutes and roll it back after, that way you have tem minutes to test configuration and allow rollback. You can place any value you want for your test time)

Hey there,

I'm getting back to you and with my problem still there.

From what I can see with wireshark on the DHCP server, the requests are properly relayed by the switch and an offer is made by the DHCP server with the proper parameters. However, the offer seems to never reach its destination.

The DHCP helper configuration is still the one I copied in one of my previous posts:

helpers {
    bootp {
        relay-agent-option;
        description "DHCP Relay";
        server 192.168.6.19;
        maximum-hop-count 10;
        minimum-wait-time 0;
        client-response-ttl 20;
        interface {
            vlan.1305;
        }
    }
}

 From what I understood of the configuration guides aforementioned, I must only declare the requests listening interfaces (i.e. the interfaces in the networks where requests are emited). I really don't know what I'm missing ...

Thanks for the help!

EDIT: Nevermind, it was a bad firewall configuration, the offer was being discarded before reaching the switch. My bad.

So it is working properly 🙂

Thanks everyone.

I also think that dhcp-pool is a key word for another option.  So you need to select another variable for your server group name.

set server-group server-group-name ip-address