RE: GRE Tunnels and MPLS

["Rettke, Brian" <Brian.Rettke () cableone biz>]

It appears that about half of our web traffic is now being dropped, so problems continue. I'll have to double check MTU 
and TCP adjust-mss settings, but other than that I have no idea. I've heard that there are some issues with MPLS using 
some of the 67xx linecards, and apparently this is going to be a huge problem for us.
________________________________________
From: Shimol Shah [shimshah () cisco com]
Sent: Monday, November 08, 2010 1:19 PM
To: nanog () nanog org
Subject: Re: GRE Tunnels and MPLS

Good deal. Sounds like a plan.

Shimol

On 11/8/10 2:00 PM, Rettke, Brian wrote:
> This seems to be working now with the 'mls mpls tunnel-recir' command entered. There are some potential downsides, 
> but this should get things up and running until I create the new backup tunnels (GRE over IPSec) on a connected 
> router that is not MPLS-enabled. Thanks!
>
> Sincerely,
>
> Brian A . Rettke
> RHCT, CCDP, CCNP, CCIP
> Network Engineer, CableONE Internet Services
>
>
> ------------------------------
>
> Message: 6
> Date: Thu, 04 Nov 2010 16:49:55 -0400
> From: Shimol Shah<shimshah () cisco com>
> Subject: Re: GRE Tunnels and MPLS
> To: nanog () nanog org
> Message-ID:<4CD31C73.80004 () cisco com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Do you have recir enabled ? If not, good one to enable and check for
> status of issue.
>
> http://www.cisco.com/en/US/docs/ios/mpls/command/reference/mp_m1.html#wp1012208
>
> "If you do not enable tunnel-MPLS recirculation, the IPv4 and
> IPv4-tunneled packets that need to be labeled (for example, the packets
> that are encapsulated with an MPLS header) will be corrupted when they
> are transmitted from the Cisco 7600 series router."
>
> Shimol
>
> On 11/4/10 4:00 PM, Rettke, Brian wrote:
> > Beginning work on our implementation of MPLS for the backbone network. I've run into difficulty with our GRE 
> > tunnels. The GRE Tunnel sits on our co-lo router (a Cisco 7600), and it uses a route-map to push our 10.x modem 
> > traffic to our DHCP servers. This is because the backbone is not complete and DHCP traffic needs to traverse the 
> > internet. What I have found is that when I enable basic MPLS on the co-location interfaces that head back to the 
> > individual systems, DHCP traffic still works, but ICMP and other 10.x traffic dies. There is also an intermittent 
> > problem with DHCP when it is enabled, where not all DISCOVERS are answered. I've tried everything I can think of, 
> > including adjusting MTU and TCP MSS. It only seems to impact when the co-location router has a GRE tunnel on one 
> > buffer, which it terminates, and then it has to encapsulate traffic with an MPLS tag before sending out of the other 
> > buffer. Theoretically, it should work, but I can't figure out if there is some pro
b
> lem with MPLS' interaction with the tunnel. Has anyone encountered something similar?
> > Sincerely,
> >
> > Brian A . Rettke
> > RHCT, CCDP, CCNP, CCIP
> > Network Engineer, CableONE Internet Services