Certain destination IP addresses are not routable within certain parts of the network, and appear to loop. This has been narrowed down to the label swap on a Cisco 6500 for the next hop of a GRE tunnel [point2point]. As per the LFIB, the Cisco 6500 is appending label 133 for network 10.10.32.1 and sending it out tun0, but appears to be snatching the packet back again, as it has a local label of 133 for the network 10.10.32.70/32 . ##Traceroute from test router (simplified for readability) 10.10.64.220 and 10.8.8.2 are c6500 interfaces, the latter being the GRE interface. [admin@rtr3] > /tool trace 10.10.32.1 # ADDRESS STATUS 1 10.10.32.137 <MPLS:L=873,E=0> **local-label for 10.10.32.1 2 10.10.64.220 <MPLS:L=71,E=0> ** local-label for 10.10.32.1