Hello Curtis, Thank you for your comments. But from what did you get conclusion of 'research projects'? We not only have a deployment experience but also strict large-scale system data analysis.
Following is my reply: 'No SPF is required for FRR to provide protection, restoring traffic flow though sometimes on a suboptimal path.' --Is FRR only used within domain? If so, it can be counted as a drawback. And LDP FRR cannot guarantee that the calculated path is the optimal path, leading to the emergence of new link congestion. But FAT TREE architecture network is a non-blocking network. 'One commercial CSPF measured about a decade ago completed in 30-40msec on a test topology of 450. That was on a 300 MHz or less PPC or Pentium-2. Todays processors are an order of magnitude faster, so we could expect (with order NlogN scaling of SPF) to get about the same SPF time on a topology of 4K or more nodes with no improvements in software.' --As seen from the above CSPF business application data, there is a linear correlation between the convergence time and the number of topologies, while it is not sensitive to the FAR. To compare the FRR and FRR, the working process of the LDP FRR technology is described as follows: 1) Running LDP protocol in the network, it works as DU (downstream independent) label distribution + orderly label control + free label retention. (Disadvantage :additional protocol overhead) In the above case, there are two paths from R1 to R5, R5 initiates multi-label mapping message to the upstream. Eventually, R2 and R3 respectively assign labels to R1 for reaching R5, among which, the label distributed by R2 is the primary label, the label distributed by R3 can be used as a backup. (Disadvantage: the irregular topology leads to complex routing and prone to cause more serious link block) 2) Specify one equipment port of the LSR as the backup of another equipment port. 3) Equipment maintenance label forwarding table: As the port backup has not been implemented, one label forwarding table has only one next hop and label, and the label is distributed for FEC by the LDP peer connected to the next hop of the routing of FEC. After the port backup is implemented, if the next hop of a label forwarding table is the protected port, add a next hop and label for the entry, and the label is distributed for FEC by the LDP peer connected to the backup next hop. (Disadvantage: large protocol database overhead and processing overhead) 4) Equipment maintenance of the working status of each port (normal/failure). 5) Packets reach the next hop, and are forwarded to the destination according to the corresponding label forwarding table. It can be seen from the above FRR processing that FRR has the following disadvantages compared to FAR: 1) Additional protocol overhead: For the protection of links, nodes and paths, it is necessary to set up a backup LSP respectively, which causes unnecessary overhead and complex protocol processing; (there is no such protocol overhead for FAR, and because FAR is based on regular topology, path protection and switching process are simple.) 2) Backup LSP failures may exist. As there is no protection mechanism, it cannot fast reroute when it fails; (FatTree network architecture has multiple natural selection.) 3) There is a linear correlation between the convergence time and the number of topologies, while it is not sensitive to the FAR. 4) LDP FRR cannot guarantee that the calculated path is the optimal path, leading to the emergence of new link congestion. But FAT TREE architecture network is a non-blocking network. Best. Richard
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