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[EX/QFX] ZTP DHCP client cannot get IP with /31 netmask

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Article ID: KB33987 KB Last Updated: 11 Jun 2019Version: 1.0
Summary:

This article explains why QFX5100/5200 and EX4300 device cannot use /31 address allocated via ZTP. 

Symptoms:

When trying to perform ZTP (zero touch provisioning) of a QFX5100-24X, the device will correctly send a DHCP request and receive the DHCP response, but then seems to ignore the response and do nothing.

Looking at /var/log/dhcp_logfile, the following message is seen:

Oct 12 16:24:22.338724 [WARN] [default:default][PXY][INET][irb.0][SID=0] jdhcpd_client_process_ack_packet: Invaild ip/mask (network or broadcast address) 4, discard
Cause:

The DHCP client always appear as "requesting" and can't load the allocated IP address.

root> show dhcp client binding              
IP address        Hardware address   Expires     State      Interface
0.0.0.0           44:aa:50:2a:17:00  0           REQUESTING  irb.0               
0.0.0.0           44:aa:50:2a:17:01  0           SELECTING  vme.0               
Solution:

Change address pool on the DHCP server with /30 subnet.

Or upgrade the device to 14.1X53-D50 or higher. For more information, refer to PR​1298234 - On QFX Series platforms with ZTP environment, the DHCP clients are not getting an IP address with /31 subnet in server configuration.

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