# Neighbor Session Solutions for Integrated Routing Protocols
## 3 Aspects Important for Supporting Multiple Network Protocols  
Based on the long-term experience of the members of the Department of Information Networks in the field of network protocols, as well as current trends in the field of dual-stack routing protocols, we proceed to narrow the field of research. Based on the analysis of the available research papers reviewed in the introduction, we focus on the support of multiple network protocols from the point of view of the protocol used for the transport (transmission) of routing information and on the issue of the number of neighbor sessions specifically for the area when multiple network protocols are deployed in the network, as this issue has not been resolved so far. In the matter of the used transport protocol, we are interested in the transport solution, both concerning the layer of the communication model (L2 vs. L3), as well as the issue of the transmission of the routing information itself. In the area of neighborship, we are similarly interested in the issues of solving neighborship relations, again both at the layer of the communication model, as well as the L3 protocols used. Based on the analysis, we manage to identify four possible classes of combinations of routing information transport solutions and the number of neighbor sessions concerning several network protocols used, which are shown in Figure 1.  
As can be seen from Figure 1, the possible combinations of the solution, let us call them Protocol Integration Solution Classes (PISCs), are as follows:  
Figure 1: Protocol Integration Solution Classes (PISCs). PISC1: addressing the transport of routing information on the link layer, neighborship management specific to each network protocol;
2. PISC2: transport on the link layer, one neighborship for all network protocols used;
3. PISC3: transport at the network layer, a separate neighborship for each network protocol;
4. PISC4: transport at the network layer, one neighborship for all network protocols. The current routing protocols supporting dual-stack IP routing can be divided as follows:  
EIGRP, as it uses its own RTP transport protocol and encapsulates its packets directly into the IP protocol while creating separate adjacencies for each network protocol, is classified as PISC3. The OSPFv3 routing protocol, as mentioned in Section 2.2, creates separate adjacencies for each network protocol and sends their messages in both cases using the IPv6 network protocol. Therefore, like EIGRP, it is classified as PISC3. Due to its design for OSI networks and its protocol independence, IS-IS is classified as PISC2, as it uses link layer frames directly for message transmission and creates only one neighborship in the case of the transmission of routing information of both IPv4 and IPv6 protocols. The only exception is the routing protocol BGP with multi-protocol extension (MP-BGP), which we can classify in both PISC3 and PISC4 since it allows both IPv4 and IPv6 information to be transmitted within one neighborship. Still, it is also possible to create multiple neighborships and transmit routing information separately as described in Section 2.1. When considering the issue of dual-stack addressing and its impact on protocol design, it is necessary to think about the implementation areas of the parts of the routing protocol related to the PISC identified above. Therefore, for each of the classes, we subsequently analyze the related implementation areas or functions (hereinafter referred to as service) on which a specific solution has a direct impact. The functions of specific currently available routing protocols serve as inspiration.