# Note

Of course, the break-even scalability point isn't the only reason to consider a particular type of protection. You also need to consider things such as where your failures occur, how often they happen, how much data you have to protect, and so forth.

Given the formula and assumptions here, the break-even point for link protection is at four nodes, and node protection is at ten nodes.

It should be obvious that path protection is always just at the break-even point, because Fn = Ln. This assumes that multiple LSPs are not protecting a single LSP.

Table 9-16 shows different numbers of nodes, the total number of LSPs used in the network (assuming that all links in the TE portion of the network are to be protected), and the number of protection LSPs used. In this table, the average degree of connectivity (D) is 3.

 Number of Number of Number of Number of Primary LSPs Used in LSPs Used in LSPs Used in Number of LSPs(Rn * Link Node Path Nodes (Rn) (Rn - 1)) Protection Protection Protection
 1 0 3 9 0 10 90 30 90 90 20 380 60 180 380 30 870 90 270 870 40 1560 120 360 1560 50 2450 150 450 2450 60 3540 180 540 3540 70 4830 210 630 4830 80 6320 240 720 6320 90 8010 270 810 8010 100 9900 300 900 9900 110 11,990 330 990 11,990 120 14,280 360 1080 14,280 130 16,770 390 1170 16,770 140 19,460 420 1260 19,460 150 22,350 450 1350 22,350

The number of LSPs used in node protection is the formula Rn * D * (D - 1) plus the number of LSPs in link protection (Rn * D). So the entire formula is

which reduces to Rn * D2.

Why do you need both link and node protection? Because if you have LSPs that terminate on a directly connected neighbor, you can't node-protect that neighbor; you need to link-protect it. You might not always need to link-protect every node (not all nodes are TE tunnel tails), but the number of additional LSPs is so small that it's not worth calculating and trying to factor out here.

Figure 9-11 shows a graph of link, node, and path scalability. Figure 9-12 shows a graph of only the link and node scalability numbers, because it's easier to see the difference between these two if path protection isn't in the way. It's important to note, however, that the graphs in both figures use the exact same data. The reason it's hard to see link and node protection numbers on the path protection graph is because of how poorly path protection scales to large numbers.