# SVDC: Synchronous Update with the Division and Combination of SRv6 Policy
###### Abstract  
With the expansion of network scale, new network services are emerging. Segment Routing over IPv6 (SRv6) can meet the diverse needs of more new services due to its excellent scalability and programmability. In the intelligent 6-Generation (6G) scenario, frequent SRv6 Traffic Engineering (TE) policy updates will result in the serious problem of unsynchronized updates across routers. Existing solutions suffer from issues such as long update cycles or large data overhead. To optimize the policy-update process, this paper proposes a scheme called Synchronous Update with the Division and Combination of SRv6 Policy (SUDC). Based on the characteristics of the SRv6 TE policy, SUDC divides the policies and introduces Bit Index Explicit Replication IPv6 Encapsulation (BIERv6) to multicast the policy blocks derived from policy dividing. The contribution of this paper is to propose the policy-dividing and combination mechanism and the policy-dividing algorithm. The simulation results demonstrate that compared with the existing schemes, the update overhead and update cycle of SUDC are reduced by 46.71% and 46.6%, respectively. The problem of unsynchronized updates across routers has been further improved. SRv6; policy updating; synchronization; TE +
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0000-0001-9911-1 network conditions and traffic demands [9; 10; 11; 12]. As a result, the SRv6 policies will be updated more frequently in an intelligent 6G network. An SRv6 policy update involves numerous new policy entries and affects several routers in the network at the same time [13]. However, due to various factors, the activation time of each new policy entry on the corresponding target router may vary [14; 15]. Therefore, from the initial policy push to the completion of policy updates across routers, partially legacy policies and partially new policies take effect simultaneously. The coexistence of legacy and new policies increases the risk of network congestion, thus introducing instability to the network [16; 17]. The reasons for this phenomenon include but are not limited to the following two points:  
1. Numerous policy entries in one single update: SRv6 TE policy updates will be more frequent in the intelligent 6G scenario. Consequently, each centralized computation yields numerous strategies, resulting in a substantial number of new policy entries waiting for distribution. There is a noticeable delay between distributing the first and last policy. The more policy entries per update, the longer the delay. Accordingly, the problem of unsynchronized policy updates across routers will be more serious. 2. The serial distribution of policies: Numerous new policy entries are obtained through one centralized computation. These new policies are queued within the controller and are waiting to be distributed to the corresponding target routers. All these new policies are not distributed at the same time. Instead, they are distributed one after another in a unicast manner to their corresponding target routers. Consequently, the distribution time of each new policy varies. Due to the time lag between the distribution of each new policy, the policy updates across routers are unsynchronized. The key to improving the problem of unsynchronized policy updates across routers is to improve the efficiency of policy distribution and shorten the time lag between the activation of each new policy. An SRv6 policy entry is represented in the form of a Segment Identifier (SID) list [18]. In other words, it is a sequence formed by multiple SIDs. Based on this fact, this paper proposes a scheme called SUDC. It can reduce the time lag between the activation time of each new policy and improve the problem of unsynchronized updates among routers, thus mitigating the risk of network failure due to instability. In brief, the primary contributions of our work are presented as follows:  
1. We propose an SRv6 TE policy-dividing and combination mechanism to improve the efficiency of policy distribution. 2.