OSPFv2中，提到点到点链路可以是unnumbered，不编号，不分配IP地址
12.4.1.1. Describing point-to-point interfaces
For point-to-point interfaces, one or more link
descriptions are added to the router-LSA as follows:
o If the neighboring router is fully adjacent, add a
Type 1 link (point-to-point). The Link ID should be
set to the Router ID of the neighboring router. For
numbered point-to-point networks, the Link Data
should specify the IP interface address. For
unnumbered point-to-point networks, the Link Data
field should specify the interface's MIB-II [Ref8]
ifIndex value. The cost should be set to the output
cost of the point-to-point interface.
o In addition, as long as the state of the interface
is "Point-to-Point" (and regardless of the
neighboring router state), a Type 3 link (stub
network) should be added. There are two forms that
this stub link can take:
某博文中写道，连接相邻交换机的两个接口的链路可以不分配IP子网，也就是连接两个路由器的两个接口也可以不分配IP地址。
Can we get around the requirement of configuring IPv4 subnets on links that connect two routed interfaces on adjacent switches? Of course – we’ve been using unnumbered interfaces on point-to-point links for ages. It’s just that the routing protocol programmers haven’t realized the days of thick coax cable are gone; in this century most people use Ethernet on point-to-point links. There’s even a 6-year-old informational RFC describing this idea .
该博文还写道，在OSPFv2中，将两个路由器之间的链路配置成不编号接口可以使其变为纯粹的拓扑元素，从而简化网络配置，路由信息库近包括真实网络，存储空间和SPF也可以更快。此外，这样还可以节省IP地址。
And now for the claims
The Cumulus documentation claims:
In OSPFv2, configuring unnumbered interfaces reduces the links between routers into pure topological elements, and thus dramatically simplifies network configuration and reconfiguration. In addition, routing database contains only the real networks, hence memory footprint is reduced and SPF is faster.
Let’s walk through all of these claims:
Configuring unnumbered interfaces reduces the links between routers into pure topological elements
Translated into engineering terms: the Type-1 (router) LSA no longer contains the stub networks for inter-router subnets. You can do something similar on Cisco IOS with OSPF prefix suppression .
… and thus dramatically simplifies network configuration and reconfiguration.
Marketese for “ we don’t check IP subnets in OSPF hello packets ”.
In addition, routing database contains only the real networks,
I don’t know what they call the routing database . OSPF database contains exactly the same number of LSAs, the routing table does contain smaller number of routes (but see also prefix suppression).
… hence memory footprint is reduced and SPF is faster.
Memory footprint is reduced. SPF speedup is probably measured in per mils – after all, the router considers the stub networks attached to Type-1 router LSAs only in the second (distance vector) part of the SPF algorithm, which has linear complexity.
OSPFv2中提到，可能一个路由器的所有点到点接口都是未编号的点到点链路，在这种情况下，路由器应该被分配一个IP地址，这个地址应该在router-LSA中通告。
[2]It is possible for all of a router's interfaces to be unnumbered
point-to-point links. In this case, an IP address must be assigned
to the router. This address will then be advertised in the router's
router-LSA as a host route.
对于卫星网络：
如果卫星的所有点到点链路（星间链路就是点到点链路）都不用分配IP地址的话，只需要为每个路由器（卫星）分配一个IP地址即可。
不知道这样会带来什么问题？高层卫星和低层卫星之间星间链路切换时会有什么问题？