mGRE over MPLS questions

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Sep 25th, 2013
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I have a dual-hub mGRE network setup over an MPLS network.  I am using EIGRP for routing and it generally seems to be working well as far as data and routing go.  VoIP is another matter.  We are seeing inconsistent reports on call quality.  We have QoS setup with service provider and on mGRE tunnels.   Since all traffic goes over MPLS we are not using IPSec.  Utilization on the circuits is very low.  Most circuit usually run only 20-40% utilization.


So I start digging around and found two things that seem odd:


1) When I do "sho ip nhrp" I notice most of the registrations have the NAT flag set.  This I find out because there is no NATTing being done anywhere.


2) NHRP registration routinely counts down to 0:00 before re-registering.  I was under the impression that a client will refresh its registration at 1/3 interval of nhrp holdtime but this doesn't seem to be working.  I currently have holdtime set at 28800 because all IPs are static.  I have tried other holdtime settings and also tried setting the ip nhrp registration timeout but registration still counts down to 0:00.


Should I be worried about this?  Or should I keep looking for another problem?


Thanks,

Diego

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sebastian.lemke Thu, 09/26/2013 - 07:52
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Hi,


1) "This  setting is on NHRP mapping entries that are from NHRP registration  packets. This indicates that the remote node (NHS client) supports the  NHRP NAT extension type for supporting dynamic spoke-to-spoke tunnels to  or from spokes behind a NAT router. This flag does not mean that the  spoke (NHS client) is behind a NAT router. "

(http://www.cisco.com/en/US/docs/ios/12_4/ip_addr/configuration/guide/hadnhrp_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1067931)


2) Usually NHRP registrations are refreshed at a 3rd of the holdtime as you said. That's what I see in my environment. You should have closer look here. Nevertheless, I wouldn't expect bad call quality caused by NHRP problems. If there was a problem, the calls would probably get interrupted.


Regards

DIEGO ALONSO Thu, 09/26/2013 - 16:46
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Seba:


The doc you reference on the NAT flag seems to be very clear.  What bothers me is that it appears to be random.  I have about 20 routers on the mGRE network.  At any one time, "show ip nhrp" will show about half with the NAT flag.  I would be happier if I could find some consistency on this but I guess I will have to live with it.


The sympton I get from spoke-to-spoke VoIP callers is that when they get a bad connection they immediately hang up and call again and the second call is clear.  I thought this might have to do with the spoke initially being routed thru the hub and then switching to direct link with the other spoke after learning spoke NBMA address.


I will keep digging.  Thank you very much.


Rgds,

Diego

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