IP Addresses and Services Configuration Guide for Cisco 8000 Series Routers, IOS XR Releases

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IP Addresses and Services Configuration Guide for Cisco 8000 Series Routers, IOS XR Releases

Direct-attached gateway redundancy

Updated: August 12, 2026

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Explains how direct-attached gateway redundancy provides Layer 3 failover by using gratuitous ARP signals and RIB route advertisement for OSPF distribution, enabling subsecond redundancy with directly connected devices.

Direct-attached gateway redundancy (DAGR) is a Layer 3 redundancy feature that

  • uses gratuitous Address Resolution Protocol (ARP) messages as failover signals

  • advertises routes in the Routing Information Base (RIB) for Open Shortest Path First (OSPF) distribution, and

  • supports subsecond failover without MAC learning, MAC flooding, or an intervening Ethernet switch.

Use with connected redundant devices

Some connected devices use proprietary Layer 2 mechanisms instead of routing protocols.

Examples include redundant base station controllers and multimedia gateways with aggressive failover requirements.

These mechanisms can resemble Virtual Router Redundancy Protocol (VRRP).

Interoperability qualification

One-to-one Layer 2 redundancy mechanisms can differ because they are proprietary.

Qualify interoperability before you deploy DAGR with IP mobile equipment.

Restrictions of direct-attached gateway redundancy

Plan the direct-attached gateway redundancy (DAGR) deployment without these unsupported capabilities:

  • DAGR does not support IPv6.

  • DAGR does not support Ethernet bundles.

  • DAGR does not support non-Ethernet interfaces.

  • DAGR does not support hitless ARP process restart.

  • DAGR does not support hitless route switch processor failover.

Configure DAGR

Configure direct-attached gateway redundancy (DAGR) for a peer that uses gratuitous Address Resolution Protocol (ARP) as a failover signal.

This example configures peer 192.0.2.1 on interface HundredGigE 0/0/0/1.

Before you begin

Confirm that the deployment complies with all DAGR restrictions.

Identify the interface, peer IPv4 address, route preferences, and timer values.

Follow these steps to configure DAGR.

Procedure

  1. Enter DAGR configuration mode.

    Example:

    Router# configure
Router(config)# interface HundredGigE 0/0/0/1
Router(config-if)# arp dagr

  2. Configure peer IPv4 address 192.0.2.1.

    Example:

    Router(config-if-dagr)# peer ipv4 192.0.2.1

  3. Set the normal and priority route distances.

    Example:

    Router(config-if-dagr-peer)# route distance normal 140 priority 3

  4. Set the normal and priority route metrics.

    Example:

    Router(config-if-dagr-peer)# route metric normal 84 priority 80

  5. Set the query timer to 2 and the standby timer to 19.

    Example:

    Router(config-if-dagr-peer)# timers query 2 standby 19

  6. Set the priority timeout to 25.

    Example:

    Router(config-if-dagr-peer)# priority-timeout 25
Router(config-if-dagr-peer)# commit

  7. Display the running DAGR configuration.

    Example:

    Router# show running-config interface HundredGigE 0/0/0/1
interface HundredGigE 0/0/0/1
 arp dagr
  peer ipv4 192.0.2.1
   priority-timeout 25
   route distance normal 140 priority 3
   route metric normal 84 priority 80
   timers query 2 standby 19
!

  8. Verify the operational state of the DAGR groups.

    Example:

    Router# show arp dagr
Interface              Virtual IP   State   Query-pd  Dist  Metr
HundredGigE0/0/0/1     192.0.2.1    Active  None      150   100
HundredGigE0/0/0/1     192.0.2.45   Query   1         None  None