LINK-3-UPDOWN vs LINEPROTO-5-UPDOWN

This post describes the difference between LINK and LINEPROTO syslog messages.

%LINK-3-UPDOWN

  1. Layer 1
  2. it is down in case of cable unplugged, wrong cable, shutdown command, speed mismatch (ethernet), device on the other end of cable is powered off

%LINEPROTO-5-UPDOWN

  1. Layer 2
  2. software handling the link claims that the interface is unusable
  3. if Layer 1 is down then this is also down
  4. if Layer 1 is up it can be down – for example if physical link works properly but ppp session can not be established (incorrect password, etc).

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