Router latency during the night

[bsciarra1]

Good evening.  I've had a strange problem for about a week.  My router is a 3745 with a 9mb multilink circuit.  This is used to route for our mpls WAN links between our branches.  AT&T is our mpls provider. 

During the day when everyone is at work my router runs fine.  At night when there is no load on the router I get latency, average in the 150 msecs.  In the morning when people come to work everything runs well. 

I know about the latency because my NMS sends me emails when the average ping time exceeds a certain amount of msec for a certain amount of time.  And I've been getting these emails all night long.  I know there is barely no traffic because I view my netflow collector for the overnight hours and there is basically nothing going on except snmp requests from my NMS and night time backups.

AT&T says nothing is going on on their end.

It almost seems like when the router has very little traffic it runs bad, then when people show up to work and traffic picks up it runs more efficiently.  Does this behavior make any sense?  Has anyone seen or heard of this before and know what this behavior may be indicative of?

Let me know, thanks...

[paolo bevilacqua]

Session in router at night and check on things first hand.

Maybe some PC backup is being made.

[Joseph W. Doherty]

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Posting

Well you described just one router, your 3745 with 6 (?) bundled T1s.  (MLPPP or ATM IMA?)  What's the other side?  Since you also mention MPLS, and branches (plural), can the combination oversubscribe your 9 Mbps?  You also mention "night time backups", do you use any QoS configurations, uses any of AT&T's supported MPLS QoS models, or do you treat all traffic alike?