What is a DHCP Proxy Agent?

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Now that we know what DHCP relay agents are, we will find out another DHCP agent, a DHCP proxy agent today.

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  • 1. NETMANIAS TECH-BLOG Please visit www.netmanias.com to view more posts What is a DHCP Proxy Agent? September 1, 2013 | By Chris (tech@netmanias.com) | Netmanias Tech-Blog | www.netmanias.com Now that we know what DHCP relay agents are, we will find out another DHCP agent, a DHCP proxy agent today. What a DHCP relay agent does is simply relay broadcast DHCP packets (DHCP Discover/Request) to DHCP server(s) located in other subnets whenever it receives packets from a DHCP client residing in that same subnet. On the other hand, a DHCP proxy agent not only relays the DHCP packets between subnets, but also acts on behalf of a DHCP server, while also acting as a DHCP client. That is, it acts as a DHCP server to the DHCP client, but act as a DHCP client to the DHCP server. The following figure shows a comparison between the DHCP relay agent and the DHCP proxy agent. The DHCP relay agent simply relays only the broadcast packets used in IP address allocation/lease procedures while the DHCP proxy agent, performing the functions of both a DHCP server and client, relays from one to the other all DHCP packets (Broadcast or Unicast) used in IP address allocation (lease), IP address renewal and IP address release procedures. PC Relay DHCP IP Allocation Procedure DHCP Offer DHCP Request DHCP Ack Proxy DHCP IP Allocation Procedure DHCP Relay DHCP Discover PC DHCP Discover DHCP Discover DHCP Discover DHCP Offer DHCP Offer DHCP Offer DHCP Request DHCP Request DHCP Request DHCP Ack DHCP Ack DHCP Ack IP Renewal Procedure DHCP Request DHCP Request DHCP Ack DHCP Ack IP Release Procedure IP Release Procedure DHCP Release DHCP Release DHCP Client DHCP Server IP Renewal Procedure (a) DHCP Relay Agent DHCP Request DHCP Ack DHCP Release (b) DHCP Proxy Agent Then what are the benefits of using a DHCP proxy agent instead of a DHCP relay agent?  Because the IP address of a DHCP server is not viewable to users (DHCP clients), the DHCP server is protected from external attacks, such as Denial of Service (DoS), which targets the server (DHCP clients can only see the IP address of a DHCP proxy agent).  Because the DHCP proxy agent keeps a list of all user IP addresses allocated through DHCP messages, it can create an IP-to-MAC binding table based on the information. This allows the agent to block any traffic from unauthorized users whose IP addresses have not been allocated through DHCP 1
  • 2. Netmanias Tech-Blog: What is a DHCP Proxy Agent? procedures (i.e. static IP users). Actually, we “Netmanias”, have once applied such security function to a network operated by one of our customers (a Dutch telecom operator) by enabling a DHCP proxy agent in Juniper BRAS when we provided the System Integration (SI) services. Why does a user recognize the IP address of a DHCP proxy agent as the IP address of a DHCP server?  That’s because the proxy agent replaces the IP address of a DHCP server with the IP address of the DHCP proxy agent in the “DHCP Server Identifier (Option 54)” field before forwarding it to the user. 2
  • 3. Netmanias Research and Consulting Scope 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 eMBMS/Mobile IPTV CDN/Mobile CDN Transparent Caching BSS/OSS Services Cable TPS Voice/Video Quality IMS Policy Control/PCRF IPTV/TPS LTE Mobile Network Mobile WiMAX Carrier WiFi LTE Backaul Data Center Migration Carrier Ethernet FTTH Wireline Network Data Center Metro Ethernet MPLS IP Routing CDN Transparent Caching Analysis Networks eMBMS LTE IMS Infrastructure Services Analyze trends, technologies and market Report Technical documents Blog One-Shot gallery Concept Design DRM POC Training Wi-Fi We design the future protocols IP/MPLS We design the future Carrier Ethernet We design the future Consulting Visit http://www.netmanias.com to view and download more technical documents. Future About NMC Consulting Group (www.netmanias.com) NMC Consulting Group is an advanced and professional network consulting company, specializing in IP network areas (e.g., FTTH, Metro Ethernet and IP/MPLS), service areas (e.g., IPTV, IMS and CDN), and wireless network areas (e.g., Mobile WiMAX, LTE and Wi-Fi) since 2002. Copyright © 2002-2013 NMC Consulting Group. All rights reserved. 3