- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
Loop-free alternates (LFAs) have been developed for fast reroute (FRR) in intradomain IP networks. They are simple, standardized, and already offered by several vendors. However, LFAs have two major drawbacks. They often cannot provide failure protection against all single link or node failures in spite of physical connectedness, and some LFAs cause routing loops in scenarios with node or multiple failures.
LFAs may be applied for various reasons that we call applications in this work. We propose several definitions for LFA coverage that quantify the application-specific utility of LFAs available in the network. The availability of LFAs and whether they can cause routing loops heavily depend on the IP routing which is determined by the choice of administrative IP link costs. To maximize the benefit of LFA usage, we optimize the IP link costs using LFA coverage as objective function. We demonstrate the feasibility and effectiveness of that approach in several test networks, and show that the choice of the right optimization function is crucial to maximize LFA coverage. However, maximizing LFA coverage can lead to significant traffic imbalance and may result in high link loads. Therefore, we suggest Pareto-optimization and demonstrate that resulting link costs can lead to both high LFA coverage and low link loads.
In IP networks, failures occur on a regular basis and often last only for a short time . The distributed IP rerouting process is simple and robust , but it may be too slow for applications and services that require continuous network availability . Recently, fast reroute (FRR) mechanisms have been proposed for IP networks . With IPFRR, a router can detour traffic around a failure location immediately after it has detected that the regular next-hop is no longer reachable. This reduces the time during which packets are lost from several seconds down to less than 50 ms. Then, regular IP rerouting is triggered. Therefore, the traffic affected by the failure is forwarded by IP-FRR mechanisms only until the rerouting process completes or the failure disappears.
Loop-free alternates (LFAs) constitute a simple fast reroute mechanism for IP networks (IP-FRR) and it is the only IP-FRR mechanism that is already standardized. However, LFAs usually cannot protect all traffic in a network even against single link failures and some LFAs may create extra-loops in case of node and multiple failures. LFAs may be applied to reduce lost traffic between the detection of a failure and the completion of IP rerouting, to improve the availability for some traffic aggregates, or to protect all traffic on a link to delay IP routing if that link fails. In this work, we looked at LFA coverage in 10 test networks from an application point of view. Therefore, metrics of interests are traffic loss due to missing LFAs, percentage of end-to-end protected traffic, and percentage of fully protected links. Moreover, we differentiated between general LFAs and those that avoid extra-loops under any condition. In contrast, previous work studied LFA coverage only as percentage of protected destinations and potential extra-loops were not considered.