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Path Selection Tie-Breaking
If more than one path is available after the rules
from the previous section have been applied, a tie-breaking rule is
applied to choose the path for the LSP. There are three tie-breaking
rules:
- Random—One of the remaining paths is picked at random.
This rule tends to place an equal number of LSPs on each link, regardless
of the available bandwidth ratio.
- Least fill—The path with the largest minimum available
bandwidth ratio is preferred. This rule tries to equalize the reservation
on each link.
- Most fill—The path with the smallest minimum available
bandwidth ratio is preferred. This rule tries to fill a link before
moving on to alternative links.
The rule used depends on the configuration. Random
is the default rule.
For the other rules, the following definitions
are needed:
- Reservable bandwidth = bandwidth of link x subscription
factor of link
- Available bandwidth = reservable bandwidth – (sum
of the bandwidths of the LSPs traversing the link)
- Available bandwidth ratio = available bandwidth/reservable
bandwidth
- Minimum available bandwidth ratio (for a path) = the smallest
available bandwidth ratio of the links in a path
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