[j-nsp] SRX300 DHCPD vs JDHCP - DHCP client issues

[John Jensen]

Hi!

I was going to ask this on the Juniper support forums but the email that
went out to my company email address is in limbo at the moment, so I
figured this would be as good of a place as any to ask.

I'm working on getting my FiOS routed through my SRX300. A couple different
places on the Internet spoke of shutting off the "old-style" DHCPD in favor
of the "new style" JDHCP. Fine, all well and good. Normally I would have
just not cared about DHCP services, except at the bottom of this page
<https://kb.juniper.net/InfoCenter/index?page=content&id=KB26898> it says:


   - Legacy DHCPD (DHCP Daemon) configuration syntax will be hidden
   starting from 15.1X49-D60 <https://kb.juniper.net/TSB16991>


Okay, sure - so I changed to JDHCP. Here's the problem:

FiOS is very particular about the DHCP options sent in the REQUEST/DISCOVER
packets in order to actually obtain a lease. Namely, (I'm pretty sure) it
wants a specific hostname, vendor-id (option 60) and client-id (option 61).
All of these I can set, which is good.

This blog post
<http://junosgeek.blogspot.com/2016/09/legacy-dhcpd-dhcp-daemon-configuration.html>
gives
a rundown of the config statements for legacy DHCP and what their
equivalent config statements are with JDHCP. But here's the problem. This:

set interfaces ge-0/0/0 unit 0 family inet dhcp client-identifier
hexadecimal 01485d36343597

Is supposed to do the same thing as this:

set interfaces ge-0/0/0 unit 0 family inet dhcp-client client-identifier
user-id hexadecimal 01485d36343597

But on the wire, this isn't the case.

Using legacy DHCP, the first command works like a champ. I get an IP from
FiOS no problem with this config - wireshark properly detects 0x01 type as
ether, and displays the MAC address of the client in the option 61 field.

Now switching to JDHCP and using the second config statement, no matter
what i put for hex or ascii, the DHCP client always inserts the interface
name as a prefix for whatever reason and it's causing my DHCP discovers to
be ignored by FiOS. So basically Wireshark only shows the length of the
option, and you see something like:

=.=.:ge-0/0/0.0:[data]

within the packet data, again regardless of which hex or ascii values I
supply to it.

This box is running 15.1X49-D45. Anyone else experienced weirdness or
undesirable prefixing of option 61 strings?

Thanks.