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[MX] Interface goes to admin down when MTU of the physical interface is changed



Article ID: KB34717 KB Last Updated: 25 Jun 2019Version: 3.0

This article provides an explanation as to why the "ifAdminStatus down" log message is reported when the operation was not performed by the administrator.



The following log message is reported in the logs indicating that an interface has gone down:

Jun 24 11:30:47.381  rtr-re0 mib2d[17617]: SNMP_TRAP_LINK_DOWN: ifIndex 791, ifAdminStatus down(2), ifOperStatus down(2), ifName xe-1/1/0.0
Jun 24 11:30:47.481  rtr-re0 mib2d[17617]: SNMP_TRAP_LINK_UP: ifIndex 791, ifAdminStatus up(2), ifOperStatus up(1), ifName xe-1/1/0.0

The administrator did not shut down the interface. However, the administrator did change the physical interface MTU:

set interfaces xe-1/1/0 mtu 2000 ‚Äč



When the protocol MTU of a physical interface is changed, all the content for that interface needs to be re-programmed again. Therefore, all the logical interfaces that are tied to the physical interface will bounce/flap. This is expected behavior.

It should be noted on most running systems that the flap will be much less than a second and that packet loss should be minimal. Only in environments that are configured for aggressive BFD liveliness settings, for example, could customer traffic be affected.


Modification History:

2019-06-25: Note added in Solution section about traffic loss and minor changes made in Symptom section.


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