[131809] in North American Network Operators' Group
GRE Tunnels and MPLS
daemon@ATHENA.MIT.EDU (Rettke, Brian)
Thu Nov 4 16:00:16 2010
From: "Rettke, Brian" <Brian.Rettke@cableone.biz>
To: "nanog@nanog.org" <nanog@nanog.org>
Date: Thu, 4 Nov 2010 13:00:08 -0700
In-Reply-To: <mailman.5670.1288900126.813.nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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 traf=
fic to our DHCP servers. This is because the backbone is not complete and D=
HCP 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 ind=
ividual 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, w=
here 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-lo=
cation 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 o=
ther buffer. Theoretically, it should work, but I can't figure out if there=
is some problem with MPLS' interaction with the tunnel. Has anyone encount=
ered something similar?
Sincerely,
Brian A . Rettke
RHCT, CCDP, CCNP, CCIP
Network Engineer, CableONE Internet Services
