IP Unnumbered Interfaces

Owned by Scott Leishman
Nov 04, 2020
2 min read

DANOS does not support unnumbered interfaces at the moment. See https://danosproject.atlassian.net/browse/DAN-207

The IP unnumbered interfaces feature allows the use of the same IPv4 address on multiple interfaces, thus conserving IP addresses. The configuration of interfaces as unnumbered allows the enabling of IP processing on interfaces without assigning an IP address to them.

To configure an unnumbered interface, specify a donor interface from which the system can borrow an IP address. Then, configure a static-interface route to forward packets through the unnumbered interface.

Only data plane interfaces and virtual interfaces (vifs) can be configured as unnumbered interfaces. For IP packets that originate from routers, the unnumbered interfaces use IPv4 addresses from donor interfaces as preferred source addresses. The donor interfaces may be either data plane or loopback interfaces.

Numbered interfaces are interfaces that have their IP addresses configured with the set interfaces command, for example, set interfaces dataplane dp0s192 address 1.1.1.1/24.

Basic IP unnumbered interface configuration

Configuring IP unnumbered interfaces on VR1

Create a loopback interface, and configure the IP address.

vyatta@vr1# set interfaces loopback lo1 address 133.0.0.1/32

Create the configuration node for the vif; assign the vif VLAN ID 60; and then assign the IP address for the vif.

vyatta@vr1# set interfaces dataplane dp0s192 vif 60 vlan '60'

Borrow the IP address from a loopback interface.

vyatta@vr1# set interfaces dataplane dp0s192 vif 60 ip unnumbered donor‐interface lo1

Add a static-interface route to reach the other network.

vyatta@vr1# set protocols static interface‐route 132.0.0.1/32 next‐hop‐interface 'dp0s192.60'

Add a route to the destination network.

vyatta@vr1# set protocol static route 192.168.2.0/0 nexthop 132.0.0.1

Configuring IP unnumbered interfaces on VR2

Create a loopback interface, and configure the IP address.

vyatta@Router# set interfaces loopback lo1 address 132.0.0.1/32

Create the configuration node for the vif; assign the vif VLAN ID 60; and then assign the IP address for the vif.

vyatta@Router# set interfaces dataplane dp0s192 vif 60 vlan '60'

Borrow the IP address from a loopback interface.

vyatta@Router# set interfaces dataplane dp0s192 vif 60 ip unnumbered donor‐interface lo1

Add the static interface route to reach the other network.

vyatta@Router# set protocols static interface-route 133.0.0.1/32 next‐hop‐interface 'dp0s192.60'

Add a route to the destination network.

vyatta@Router# set protocol static route 192.168.1.0/0 nexthop 133.0.0.1