This is going to be a weird one. Just a warning.
We are a service provider and we've deployed a Cisco 2621 XM as a CPE router terminating a
T1 we are providing to the customer site, this is part of a BGP over MPLS cloud spanning
10 customer sites in total. This is part of a Metro Ethernet MPLS operating on a 1 Gig
switched ring with Cisco 7500 routers serving as the CO routers.
The Cisco 7500 CO routers run BGP over MPLS and 9 of the 10 customer sites are operating
correctly, each site is fed by a single T1, which is provided through a Channelized DS3
card in the 7500 through a Adtran MX2820 and then terminated by a T1 Version 1 WiC card in
the Cisco 26XX of each site.
The site experiencing the issues is unable to send FTP and outgoing email on ports 20,21
and 25. The information that really makes this odd is as follows:
The site experiencing the issues works fine with Windows XP, going FTP and Email, but
various Windows NT and 2000 customers are unable to use FTP and Email at the site.
Elsewhere at the other 9 sites the customer has Windows NT and 2000 computers that work
What would be the difference between Windows XP and Windows NT traffic crossing a BGP over
MPLS cloud? The IP addresses, ports and router configurations remain the same.
I've seen this problem before, and it was a fragmentation issue. I had to create a route map and apply it to the client site so that the DF flag was cleared. This then enabled fragmentation on the client side prior to entering the MPLS CE WAN ckt facing the PE.