## 1 Introduction  
Due to the advantages of multicasting, mobility, security, and caching, information-centric networking (ICN) is considered an effective way to improve the existing network from network architecture level [1]. Compared with a traditional IP network, ICN cares more about content itself than the location of content. Following this principle, ICN decouples content addressing from routing by separating the identifier (name) and the locator of content. Nevertheless, many researchers believe that the benefits advocated by ICN require magnificent upgrades to entire network infrastructures [2], the huge costs of which make it impractical for clean-state ICN to be deployed. In order to smoothly evolve, many studies have shown interest in incremental deployment of ICN (and correlative cache system) without changing today's IP infrastructure as much as possible [2; 3; 4; 5; 6; 7]. Some ICN paradigms are implemented as an overlay top of the current internet, and these effectively utilize existing IP facilities and routing schemes, such as MobilityFirst (MF) [3] and the network of information (NetInf) [4]. The former focuses on supporting the seamless handover of terminals in mobility scenarios, and the latter was funded by the 4 WARD project and aims to improve large-scale content distribution. Meanwhile, an ICN router should be able to forward and process both IP and ICN flows at an Layer 3 (L3) network layer [5]. Another aspect of the deployment scheme is that of ICN over IP [6; 7] based on the gateway isolation, where the first link from the user's device to network uses existing IP-based protocols, such as HyperText Transfer Protocol (HTTP), Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). As an entry/out point of ICN, the gateway converts chosen protocol to ICN. However, the improvement of ICN over IP depends on the limited scope of the gateway, which makes it difficult to implement new services and applications in an entire network. There are two typical content discovery mechanisms in ICN. One is routing-by-name, which couples name resolution with content routing in a data plane. For instance, the content-centric network (CCN) [8; 9], the most widely studied ICN paradigm whose routers forward user's requests to the right port computed by content name, adopts a routing-by-name mechanism. The shortcomings of this mechanism are as follows. First of all, routers lack the capacity to save routing information for considerable amount of content. In addition, it is easy to cause large-scale routing updating when the state of each duplicate changes. The second content discovery mechanism is lookup-by-name, which accomplishes content discovery by retrieving the network addresses (NAs) of the named data object (NDO) from a dedicated device named the name resolution system (NRS). The lookup-by-name mechanism makes routers concentrate on routing and caching at the cost of signaling overhead from the NRS, which alleviates the computing pressure of routers. With the assist of resolution nodes (RNs) distributed around the network, deploying an NRS is an effective method to encourage ICN to coexist with the current IP network with high scalability [10]. A hierarchical NRS reduces the inter domain traffic and the latency of naming resolution by keeping the name information of content as close to the user as possible. Communication between the RNs of different levels can be realized by deploying a multi-level distributed hash table (MDHT) [11] in each RN. For example, the data-oriented network architecture (DONA) [12] deploys more than one logical resolution handler (RH) in every autonomous system (AS). In a hierarchical NRS, we have observed that the request packet of content name resolution is sent to a higher-level RN if the request cannot be satisfied in a lower-level RN. In other words, in this behavior pattern, the request of the NDO is sent to a higher-level cache node if it cannot be hit in a lower-level one.