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In "CCNP and CCIE Enterprise Core ENCOR 350-401 Official Cert Guide" we have this definition of max age:

Max age: This is the maximum length of time that passes before a bridge port saves its BPDU information.

Is this correct ?

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    – Ron Maupin
    Commented Dec 17, 2020 at 15:47

1 Answer 1

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In short, Max Age is the maximum age any information learned from BPDUs can have before it is dropped (aged out). In doubt, you should refer to IEEE 802.1Q.

From that book the entire section is

Max age: This is the maximum length of time that passes before a bridge port saves its BPDU information. The default value is 20 seconds, but the value can be configured with the command spanning-tree vlan vlan-id max-age maxage. If a switch loses contact with the BPDU’s source, it assumes that the BPDU information is still valid for the duration of the Max Age timer.

The second half does put it into a better perspective but it's still ambiguous. It should maybe read ... is the maximum length of time for that a bridge port saves its BPDU information.

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    Thank you for this clarification.Is the term "saves" appropriate since BPDU information is dropped ?
    – user159729
    Commented Mar 7, 2020 at 23:53
  • The wording is not very comprehensive, I've edited the answer about that.
    – Zac67
    Commented Mar 8, 2020 at 8:43
  • I definitely had the same confusion/thoughts about "saves its information" and that is what brought me to this page. In the second half of the definition they say that the info is considered valid for that period, which makes sense. In the first half of the definition, maybe they are saying the initial receipt of new information is not considered valid until after the age period, after which it "saves" it and so begins using it.
    – thorr18
    Commented Oct 11, 2020 at 21:53

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