Dell N3200-ON Networking N-Series Switches CLI Reference Guide version 6.8.0 - Page 1561

The interface should be configured as able to borrow an IP address, i.e. a routing interface with no IP address. The loopback interface is the numbered interface providing the borrowed address. The providing loopback interface cannot be unnumbered. The loopback interface is identified by its loopback interface number. It is a misconfiguration for two routers, R1 and R2, to be connected by a link where R1's interface is unnumbered and R2's interface is numbered. If a static route is configured on R2 using R1's IP address as next hop, the static route will never be installed in the routing table because the next hop is not in a local subnet. If a static route is configured on R1 using R2's IP address as next hop, the static route will be installed in the routing table. R1 will ARP for the next hop address. R2 will ignore the ARP Request because the source IP address is not in a local subnet. It is a misconfiguration to enable OSPF on both ends of an unnumbered interface without setting the OSPF network type to point-to-point. Each router will reject its neighbor's HELLOs because the source IP address is not in a local subnet. Adjacencies never progress beyond the INIT state. If three or more routers are connected to the same subnet/broadcast domain and all are configured to treat the Ethernet interface as a point-to-point link, adjacencies may not form. The OSPF database description packets intended for a specific neighbor will be processed by all neighbors, causing errors that reset adjacencies. Command History Introduced in version 6.2.0.1 firmware. Example console(config-if-vlan1)#ip unnumbered 10.130.14.55 ip unnumbered gratuitous-arp accept This command enables installation of a static interface route to the unnumbered peer upon receiving a gratuitous ARP. Syntax ip unnumbered gratuitous-arp accept Layer 3 Routing Commands 1561