A YANG Data Model for ARP

Basic ARP functionality is supported by the ietf-ip YANG data model, defined in . This document defines a YANG data model that extends the basic ARP YANG support to also cover optional ARP features, and ARP related statistics to aid network monitoring and troubleshooting. This model defines YANG configuration and operational state data nodes both for ARP related functionality formally specified in other RFCs (such as and ), and also for common ARP behaviour that is often supported on network devices. The YANG modules in this document conform to the Network Management Datastore Architecture (NMDA) . Editorial Note: (To be removed by RFC Editor) This draft contains several placeholder values that need to be replaced with finalized values at the time of publication. Please apply the following replacements: "XXXX" --> the assigned RFC value for this draft both in this draft and in the YANG models under the revision statement. The "revision" date in model, in the format XXXX-XX-XX, needs to be updated with the date the draft gets approved. The date also needs to get reflected on the line with <CODE BEGINS>.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. The following terms are defined in and are not redefined here: client server configuration data system state state data intended configuration running configuration datastore operational state datastore The following terms are defined in and are not redefined here: augment data model data node The terminology for describing YANG data models is found in .

Tree diagrams used in this document follow the notation defined in .

Neither ARP nor Proxy-ARP defines standard network management configuration models. Instead, network equipment vendors have implemented their own bespoke configuration interfaces and models. Network operators benefit from having common network management models defined that can be implemented by multiple network equipment manufacturers. This simplifies the operation and management of network devices. Some, but not all, required ARP functionality has been defined in "ietf-ip" (). Providing a standard YANG model that models these optional ARP features, which are fairly widely implemented by network equipment manufacturers, and used by network operators, is beneficial to the general goal of interoperability in the networking industry.

This data model intends to describe the processing that a protocol finds the hardware address, also known as Media Access Control (MAC) address, of a host from its known IP address. These tasks include, but are not limited to, configuring dynamic ARP learning, proxy ARP, and gratuitous ARP. There are two kinds of ARP configurations: global ARP configuration, which is across all interfaces on the device, and per interface ARP configuration.

As defined in , ARP caching is the method of storing network addresses and the associated data-link addresses in memory for a period of time as the addresses are learned. This minimizes the use of valuable network resources to broadcast for the same address each time a datagram is sent. There are static ARP cache entries and dynamic ARP cache entries. Static entries, are manually configured and kept in the cache table on a permanent basis which are defined in the ipv4 neighbor list for each interface in . Dynamic entries are added by vendor software, kept for a period of time, and then removed. We can specify how long an entry remains in the ARP cache. If we specify a timeout of 0 seconds, entries are never cleared from the ARP cache.

Proxy ARP, defined in , allows a router to respond to ARP requests on behalf of another machine that is not on the same local subnet, offering its own Ethernet media access control (MAC) address. By replying in such a way, the router then takes responsibility for routing packets to the intended destination. In the case of certain data center network virtualization, as specified in , the proxy ARP can be extended to intercept all ARP requests, including source and target IP addresses in different subnets, and those ARP requests in the same subnet to suppress ARP handling.

Gratuitous ARP enables a device to send an ARP Request packet using its own IP address as the destination address. Gratuitous ARP provides the following functions: Checks duplicate IP addresses: uses gratuitous ARP to help detect IP conflicts. When a device receives an ARP request containing a source IP that matches its own, then it knows there is an IP conflict. Advertises a new MAC address: Also in , if the MAC address of a host changes because its network adapter is replaced, the host sends a gratuitous ARP packet to notify all hosts of the change before the ARP entry is aged out. Notifies an active/standby switchover in a VRRP backup group: After an active/standby switchover, the master router sends a gratuitous ARP packet in the VRRP backup group to notify the switchover.

This document defines the YANG module "ietf-arp", which has the following structure:

This section presents the ARP YANG module defined in this document. This module imports definitions from Common YANG Data Types, A YANG Data Model for Interface Management, and A YANG Data Model for IP Management.

file "ietf-arp@2025-07-19.yang" module ietf-arp { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-arp"; prefix arp; import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } import ietf-interfaces { prefix if; reference "RFC 8343: A Yang Data Model for Interface Management"; } import ietf-ip { prefix ip; reference "RFC 8344: A Yang Data Model for IP Management"; } organization "IETF Routing Area Working Group (rtgwg)"; contact "WG Web: WG List: Author: Feng Zheng Editor: Bo Wu Editor: Robert Wilton Editor: Fan Zhang Author: Yongqing Zhu Author: Xiaojian Ding "; description "This YANG module defines Address Resolution Protocol (ARP) management, which includes static ARP configuration, dynamic ARP learning, ARP entry query, and packet statistics collection. Copyright (c) 2025 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2025-07-19 { description "Init revision"; reference "RFC XXXX: A Yang Data Model for Address Resolution Protocol (ARP)"; } container arp { description "Address Resolution Protocol (ARP)"; leaf dynamic-learning { type boolean; default "true"; description "Controls the default ARP learning behavior on all interfaces on the device, unless explicit overridden by the per-interface dynamic-learning leaf: true - dynamic learning is enabled on all interfaces by default, false - dynamic learning is disabled on all interfaces by default"; reference "RFC826: An Ethernet Address Resolution Protocol"; } } augment "/if:interfaces/if:interface/ip:ipv4" { description "Augment interfaces with ARP configuration and state."; container arp { description "Address Resolution Protocol (ARP) related configuration and state"; leaf expiry-time { type uint32 { range "30..86400"; } units "seconds"; description "Aging time of a received dynamic ARP entry before it is removed from the cache."; } leaf dynamic-learning { type boolean; description "Controls whether dynamic ARP learning is enabled on the interface. If not configured, it defaults to the behavior specified in the per-device /arp/dynamic-learning leaf. true - dynamic learning is enabled false - dynamic learning is disabled"; } container proxy-arp { description "Configuration parameters for proxy ARP"; leaf mode { type enumeration { enum disabled { description "The system only responds to ARP requests that specify a target address configured on the local interface."; } enum remote-only { description "The system only responds to ARP requests when the sender and target IP addresses are in different subnets."; } enum all { description "The system responds to ARP requests where the sender and target IP addresses are in different subnets, as well as those where they are in the same subnet."; } } default "disabled"; description "When set to a value other than 'disabled', the local system should respond to ARP requests that are for target addresses other than those that are configured on the local subinterface using its own MAC address as the target hardware address. If the 'remote-only' value is specified, replies are only sent when the target address falls outside the locally configured subnets on the interface, whereas with the 'all' value, all requests, regardless of their target address are replied to."; reference "RFC1027: Using ARP to Implement Transparent Subnet Gateways"; } } container gratuitous-arp { description "Configure gratuitous ARP."; reference "RFC5227: IPv4 Address Conflict Detection"; leaf enable { type boolean; description "Enable or disable sending gratuitous ARP packet on the interface. The default behaviour is device specific, and a deviation could be used to specify a device specific default."; } leaf interval { type uint32 { range "1..86400"; } units "seconds"; description "The interval, in seconds, between sending gratuitous ARP packet on the interface. The default behaviour is device specific, and a deviation could be used to specify a device specific default."; } } container statistics { config false; description "ARP per-interface packet statistics For all ARP interface counters, discontinuities in the value can occur at re-initialization of the management system and at other times as indicated by the value of '../../statistics/discontinuity-time' in the ietf-interfaces YANG module."; leaf in-requests-pkts { type yang:counter32; description "The number of ARP request packets received on this interface."; } leaf in-replies-pkts { type yang:counter32; description "The number of ARP reply packets received on this interface."; } leaf in-gratuitous-pkts { type yang:counter32; description "The number of gratuitous ARP packets received on this interface."; } leaf out-requests-pkts { type yang:counter32; description "The number of ARP request packets sent on this interface."; } leaf out-replies-pkts { type yang:counter32; description "The number of ARP reply packets sent on this interface."; } leaf out-gratuitous-pkts { type yang:counter32; description "The number of gratuitous ARP packets sent on this interface."; } } } } augment "/if:interfaces/if:interface/ip:ipv4/ip:neighbor" { description "Augment IPv4 neighbor list with ARP expiry time."; leaf remaining-expiry-time { type uint32; units "seconds"; config false; description "The number of seconds until the dynamic ARP entry expires and is removed from the ARP cache."; } } }

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      This section presents two simple ARP configuration examples:

      
        This example illustrates the configuration for a static ARP entry
        for peer 192.0.2.1 with MAC address 00:00:5E:00:53:AB using the model
        defined in .

        
          

  
    eth0
    ianaift:ethernetCsmacd
    
    
    
      
      
        192.0.2.1
        00:00:5E:00:53:AB
      
    
  

]]>
        
      

      
        This example illustrates the configuration of ARP entry expiry
        time, proxy ARP in 'remote-only' mode, and enabling gratuitous ARP
        with an interval of 10 minutes.

        
          

  
    eth0
    ianaift:ethernetCsmacd
    
   
    
      
      
        1200
        
          remote-only
        
        
          true
          600
        
      
    
  

        ]]>
        
      
    

    
      This document registers a URI in the IETF XML
      registry. Following the format in , the
      following registration is requested to be made:

      
        
      

      This document registers a YANG module in the YANG Module Names
      registry .

      
        
      
    

    
      The YANG module specified in this document defines a schema for data
      that is designed to be accessed via network management protocols such as
      NETCONF  or RESTCONF  .
      The lowest NETCONF layer is the secure transport layer, and the
      mandatory-to-implement secure transport is Secure Shell (SSH) . The lowest RESTCONF layer is HTTPS, and the
      mandatory-to-implement secure transport is TLS .

      The NETCONF Access Control Model (NACM) 
      provides the means to restrict access for particular NETCONF or RESTCONF
      users to a preconfigured subset of all available NETCONF or RESTCONF
      protocol operations and content.

      There are a number of data nodes defined in this YANG module that are
      writable/creatable/deletable (i.e., config true, which is the default).
      These data nodes may be considered sensitive or vulnerable in some
      network environments. Write operations (e.g., edit-config) and delete
      operations to these data nodes without proper protection or
      authentication can have a negative effect on network operations.These
      are the subtrees and data nodes and their sensitivity/vulnerability in
      the "ietf-arp" module:

      * /ietf-arp/dynamic-learning

      This leaf is used to enable ARP dynamic learning on all interfaces.
      ARP dynamic learning could allow an attacker to inject spoofed traffic
      into the network, e.g. denial-of-service attack.

      * arp/dynamic-learning

      This leaf is used to enable ARP dynamic learning on a single
      interface. ARP dynamic learning could allow an attacker to inject
      spoofed traffic into the network, e.g. denial-of-service attack.

      * interface/ipv4/arp/proxy-arp

      These leaves are used to enable proxy ARP on an interface. They could
      allow traffic to be mis-configured (denial-of-service attack).

      * interface/ipv4/arp/gratuitous-arp

      These leaves are used to enable sending gratuitous ARP packet on an
      interface. This configuration could allow an attacker to inject spoofed
      traffic into the network, e.g. man-in-the-middle attack. The default
      value for this data node is device specific, and hence users of this
      model MUST understand whether or not gratutious ARP is enabled and
      whether this could constitute a security risk.
    

    
      The authors wish to thank Alex Campbell, Reshad Rahman, Qin Wu, Tom
      Petch, Jeffrey Haas, and others for their helpful comments.



  
    
      

      

      

      

      

      

      

      

      

      

      

      

      

      
    

    
      

      

      

      

      

      
    

    
      This section presents two simple ARP configuration examples:

      
        This example illustrates the configuration for a static ARP entry
        for peer 192.0.2.1 with MAC address 00:00:5E:00:53:AB using the model
        defined in .

        
          

  
    eth0
    ianaift:ethernetCsmacd
    
    
    
      
      
        192.0.2.1
        00:00:5E:00:53:AB
      
    
  

]]>
        
      

      
        This example illustrates the configuration of ARP entry expiry
        time, proxy ARP in 'remote-only' mode, and enabling gratuitous ARP
        with an interval of 10 minutes.

        
          

  
    eth0
    ianaift:ethernetCsmacd
    
   
    
      
      
        1200
        
          remote-only
        
        
          true
          600
        
      
    
  

        ]]>