## 1 Introduction  
Nowadays, networks are inextricably interwoven with human social activities, which simultaneously presents unprecedented challenges to the future development of networks. Satellite-terrestrial networks (STNs), namely the global heterogeneous networks based on terrestrial networks and extended on space networks, use internet technologies to realize the connectivity among internet networks, mobile networks, and space networks, which have become a significant developing direction of future networks. Recent technological advances (including improvements in single-satellite performance and reductions in launching and manufacturing costs) make it possible to the deployment of low Earth orbit (LEO) satellite constellation systems, which can offer high-speed and huge-capacity communications between satellites and the ground, and thus STNs have attracted much attention in the sixth generation (6G) mobile communication technology. In terms of the structure of STNs, as illustrated in Figure 1, LEO satellite constellations play a crucial role. Unlike traditional geostationary Earth orbit (GEO) satellites, LEO satellites have the advantage of low latency, and mega-constellation systems of LEO satellites provide an effective way to realize global continuous coverage. Therefore, LEO satellite constellations are considered a promising solution for space backbone networks, capable of providing phone high-bandwidth, low-latency, and wide-ranging internet service access to users across the globe, and satellite internet is increasingly becoming an important information infrastructure. There are three active global LEO satellite initiatives that have stood out in recent years: Starlink by SpaceX, Project Kuiper by Amazon, and OneWeb backed by the government of the United Kingdom and Bharti Enterprises, which are licensed by the Federal Communications Commission (FCC) to launch 4408 [1], 3236 [2], and 716 [3] satellites in the initial phases, respectively. Generally, each satellite node in space networks has the capability of signal and data processing, and data interchange is implemented via inter-satellite links (ISLs). In the initial deployments of these constellations, it is not specified whether they plan to use ISLs, and their total throughputs without ISLs are all over 1 Tbps [4]. Since optical ISLs allow satellite constellations to serve users globally, even when a terrestrial gateway is not within the line-of-sight (LoS) of the satellite, optical ISLs are planned to be used to improve constellation system throughput in the future [3]. Like terrestrial networks, satellite networks rely on certain routing protocols to achieve data forwarding. Routing protocols are responsible for creating routing tables, describing the network topology structure, and performing routing and packet forwarding. Thus, satellite routing protocols play a crucial role in satellite network communications. Currently, Internet Protocol (IP) is the mainstream scheme for satellite networks to connect the global Internet. Specifically, satellites can perform dynamic IP routing via configuring  
Figure 1: The structure of satellite–terrestrial networks (STNs). interior/exterior gateway protocols at the terrestrial terminal, or serve as IP routing nodes in the constellation system to access the Internet [5]. However, due to the low computing power and limited memory resources on satellites, inter-satellite networks differ greatly from terrestrial networks, and how to realize IP packet routing and forwarding with high speed has become a key issue in designing LEO satellite routers. IP route lookup, also known as IP address lookup or IP lookup, is a core technology in IP routers, and its algorithm performance will directly affect the system performance of routers.