[c-nsp] strange behavior over MPLS network - remote desktop won't work

Chris Hale chale99 at gmail.com
Sun May 31 17:04:57 EDT 2009

Should be at least 1500.  I have forced the FastE ports between the two
cisco 7206's at POP H to use I have a server at POP "H" connected to an agg
switch that is connected to the 7206 on the left of POP H.  The server is
only connected via FastE, but the results are 1500 MTU:

     Resume: pmtu 1500 hops 4 back 4

This tracepath is to the CE WAN port.  All traffic from 7206's to CE is via
VLANs through wireless bridges.  All traffic between POPs is over GE ports
in NPE-G1.

Using IOS 12.4(15)T5 on 7206's, FYI.

The mpls MTU over the gige wireless backbone between the POPs was MTU1500.
I will change that to 1538 and see what happens.


On Sun, May 31, 2009 at 4:20 PM, Chris Phillips <cphillips at wbsconnect.com>wrote:

> A shot in the dark here, but what's the MTU along the path?
> I know things like Outlook Web Access won't work unless there's a minimum
> 1500 MTU.
> I highly recommend grabbing MTUroute.exe and testing this.
> http://www.elifulkerson.com/projects/mturoute.php
> Chris Hale wrote:
>> All -
>> We have a simple three node MPLS network that we've deployed for a
>> customer
>> across our backbone.  Two sites connect to POP "N" and one site connects
>> to
>> POP "H".  We have CE (Juniper J2320's) that provide OSPF updates to the PE
>> for customer routes, and Internet is also provided via a second circuit to
>> the site off POP "H".
>> Site W and Site S are off POP N.
>> Site B is off POP H.
>> POP N and POP H are connected directly to each other via GigE over
>> wireless
>> backhaul.  Sites W, S, and B are connected to POPs via wireless bridges
>> and
>> use 802.1q trunks to aggregate traffic to the core routers.
>> Here is a simple ASCII text:
>> Site W
>>   |
>> cisco 7206 (POP-N) ->---wireless backhaul gige ---->-cisco-7206
>> (POP-H)--->fastE--->cisco7206(POP-H)--->---Site B ----> Cisco ASA --->
>> Internet
>>   |
>> Site S
>> All CE routers pick up the routes from the other CE routers, and ICMP
>> works
>> fine throughout network. Users in Sites W & S can access Internet.
>> Users between Site W and Site S can use remote desktop/VNC to access other
>> desktops/servers within these sites (i.e. between Site S and Site W,
>> remote
>> desktop is fine).
>> The issue is when users in Site B try to remote desktop into Site W or
>> Site
>> S, or either Site W or S go to Site B.  Again, site S<-->W is fine.
>> I have packet captures with and without the CE routers, and I see traffic
>> going back and forth between W and B for a test on TCP 3389.  Again, pings
>> and other traffic work fine between these sites, it just seems to be
>> remote
>> desktop or VNC.  The customer can get the login window to pop up but then
>> it
>> seems to hang after a few seconds.
>> They are migrating off a p2p T1 connect between W<---->B<---->S, and they
>> used plain 1600 series routers.  Remote desktop/VNC worked fine before
>> migrating to our MPLS connections.
>> Thanks,
>> Chris
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> --
> Chris Phillips

Chris Hale
chale99 at gmail.com

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