Connected: An Internet Encyclopedia
13.1. Determining which link state is newer
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13.1. Determining which link state is newer
13.1. Determining which link state is newer
When a router encounters two instances of a link state
advertisement, it must determine which is more recent. This
occurred above when comparing a received advertisement to its
database copy. This comparison must also be done during the
Database Exchange procedure which occurs during adjacency
bring-up.
A link state advertisement is identified by its LS type, Link
State ID and Advertising Router. For two instances of the same
advertisement, the LS sequence number, LS age, and LS checksum
fields are used to determine which instance is more recent:
- The advertisement having the newer LS sequence number is
more recent. See Section 12.1.6 for an explanation of the
LS sequence number space. If both instances have the same
LS sequence number, then:
- If the two instances have different LS checksums, then the
instance having the larger LS checksum (when considered as a
16-bit unsigned integer) is considered more recent.
- Else, if only one of the instances has its LS age field set
to MaxAge, the instance of age MaxAge is considered to be
more recent.
- Else, if the LS age fields of the two instances differ by
more than MaxAgeDiff, the instance having the smaller
(younger) LS age is considered to be more recent.
- Else, the two instances are considered to be identical.
Next: 13.2. Installing link state advertisements in the database
Connected: An Internet Encyclopedia
13.1. Determining which link state is newer