--- title: DHCP Relaying Details « ipSpace.net blog | daily.dev description: A deep dive into DHCP relaying mechanics sourced directly from RFCs. Covers the basic relay process (giaddr, chaddr fields), Option 82 (Relay Agent... canonical: https://daily.dev/posts/dhcp-relaying-details-ipspace-net-blog-dujdbd2cv twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: DHCP Relaying Details « ipSpace.net blog | daily.dev og:description: A deep dive into DHCP relaying mechanics sourced directly from RFCs. Covers the basic relay process (giaddr, chaddr fields), Option 82 (Relay Agent... og:url: https://daily.dev/posts/dhcp-relaying-details-ipspace-net-blog-dujdbd2cv og:image: https://api.daily.dev/og/posts/DujdBd2cv.png og:image:alt: DHCP Relaying Details « ipSpace.net blog og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # DHCP Relaying Details « ipSpace.net blog **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 6 min read · 0 upvotes · 0 comments ## Summary A deep dive into DHCP relaying mechanics sourced directly from RFCs. Covers the basic relay process (giaddr, chaddr fields), Option 82 (Relay Agent Information) and its many sub-options including Circuit ID and Remote ID, and the more complex inter-VRF DHCP relaying scenario. For inter-VRF setups, three key sub-options are explained: Link Selection (RFC 3527), Server Identifier (RFC 5107), and Virtual Subnet Selection (RFC 6607). The post explains how these sub-options allow DHCP relay agents to bridge clients and servers in different VRFs without requiring inter-VRF route leaking, and sets up a follow-up on making DHCP work in EVPN/VXLAN environments. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How does a DHCP relay agent handle requests when the client and server are in different VRFs? For inter-VRF DHCP relaying, the relay copies the incoming interface IP (in the customer VRF) into the Link Selection (RFC 3527) and Server Identifier (RFC 5107) sub-options, adds the VPN/VRF identifier as a Virtual Subnet Selection (RFC 6607) sub-option, and sets giaddr to the outgoing interface IP reachable by the server. The server replies to giaddr; the relay uses the returned sub-options to route the reply back to the correct VRF and client — no inter-VRF route leaking required. _Network engineers navigating inter-VRF DHCP designs track RFC-level details like these on daily.dev._ ### What is the purpose of DHCP Option 82 and what sub-options does it define? DHCP Option 82 (Relay Agent Information Option, RFC 3046) lets a relay agent attach metadata to forwarded DHCP requests. Its original sub-options are Circuit ID (incoming interface) and Remote ID (end user). The IANA registry defines over 20 sub-options in total, including Subscriber ID (RFC 3993), RADIUS attributes (RFC 4014), Authentication (RFC 4030), and Virtual Subnet Selection (RFC 6607), enabling use cases from user authentication to inter-VRF routing. _Engineers designing DHCP relay policies for multi-tenant networks find Option 82 coverage like this on daily.dev._ ### Which RFC defines DHCP relaying and how does the giaddr field work? DHCP relaying is defined in RFC 1542 (referenced by RFC 2131). The relay agent sets the giaddr (gateway IP address) field in the forwarded DHCP message only if it has not already been set — meaning in a chain of relays, only the first relay sets giaddr. The DHCP server uses giaddr for subnet selection and sends its reply directly to giaddr, which the relay then forwards to the client via unicast or broadcast depending on the chaddr and broadcast flag. _Networking professionals building or debugging relay chains keep up with protocol fundamentals on daily.dev._ ## Similar posts on daily.dev - [Configuring Management IP Addresses to Virtual Network Devices « ipSpace.net blog](https://daily.dev/posts/configuring-management-ip-addresses-to-virtual-network-devices-ipspace-net-blog-ffffzfuyz) · ipSpace.net Blog · 0 upvotes · 0 comments --- [View this post on daily.dev](https://daily.dev/posts/dhcp-relaying-details-ipspace-net-blog-dujdbd2cv) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"DHCP Relaying Details « ipSpace.net blog","url":"https://daily.dev/posts/dhcp-relaying-details-ipspace-net-blog-dujdbd2cv","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/dhcp-relaying-details-ipspace-net-blog-dujdbd2cv"},"datePublished":"2026-08-11T08:55:59.509Z","dateModified":"2026-08-11T09:18:40.905Z","description":"A deep dive into DHCP relaying mechanics sourced directly from RFCs. 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