Nexus 7000 DHCP Relay

Author
Peter Welcher
Architect, Operations Technical Advisor

One of my consulting customers pointed something out to me that I hadn’t known. IP helper (now DHCP relay) works differently on the Nexus 7000 than on the 6500. The N7K imposes a VACL to filter local DHCP broadcast traffic, under the assumption that you’d be using DHCP relay when there is no local DHCP server. So if you are planning on using a local DHCP server with the DHCP relay (former helper) address providing fallback to a remote DHCP server, you need to put in a DHCP relay line for the local server as well as the remote one.

For full details and a configuration example, see https://supportforums.cisco.com/docs/DOC-14753.

Here is my version of the configuration example provided:

interface vlan 10
  ip address 10.1.1.1 255.255.255.0
  ip dhcp relay 11.2.3.4  ! remote DHCP server
  ip dhcp relay 10.1.1.2  ! localDHCP  server

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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.

 

Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
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Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.

 

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