link monitoring

Eric Kuhnke eric.kuhnke at
Thu Apr 29 21:32:05 UTC 2021

The Junipers on both sides should have discrete SNMP OIDs that respond with
a FEC stress value, or FEC error value. See blue highlighted part here
about FEC. Depending on what version of JunOS you're running the MIB for it
may or may not exist.

In other equipment sometimes it's found in a sub-tree of SNMP adjacent to
optical DOM values. Once you can acquire and poll that value, set it up as
a custom thing to graph and alert upon certain threshold values in your
choice of NMS.

Additionally signs of a failing optic may show up in some of the optical
DOM MIB items you can poll:

It helps if you have some non-misbehaving similar linecards and optics
which can be polled during custom graph/OID configuration, to establish a
baseline 'no problem' value, which if exceeded will trigger whatever
threshold value you set in your monitoring system.

On Thu, Apr 29, 2021 at 1:40 PM Baldur Norddahl <baldur.norddahl at>

> Hello
> We had a 100G link that started to misbehave and caused the customers to
> notice bad packet loss. The optical values are just fine but we had packet
> loss and latency. Interface shows FEC errors on one end and carrier
> transitions on the other end. But otherwise the link would stay up and our
> monitor system completely failed to warn about the failure. Had to find the
> bad link by traceroute (mtr) and observe where packet loss started.
> The link was between a Juniper MX204 and Juniper ACX5448. Link length 2
> meters using 2 km single mode SFP modules.
> What is the best practice to monitor links to avoid this scenarium? What
> options do we have to do link monitoring? I am investigating BFD but I am
> unsure if that would have helped the situation.
> Thanks,
> Baldur
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