[VMC on AWS ] Routed network may stop working if network address is used as on-prem endpoint device address
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[VMC on AWS ] Routed network may stop working if network address is used as on-prem endpoint device address


Article ID: 323636


Updated On:


VMware Cloud on AWS


Routed networks are unable to communicate, when either endpoint uses RFC 6598 addressing space (
Performing a trace route from VMC VM to on-premises when the on-premises endpoint IP address falls under subnet.

1 gateway (192.168.xx.xx) 0.522 ms 0.574 ms 0.521 ms
2 xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx) 1.233 ms 1.309 ms 1.380 ms
3 xxx.xxx.xxx.xxx (xxx.xxx.xxx.xxx) 0.859 ms 0.932 ms 0.906 ms
4 192.168.xx.xx (192.168.xx.xx) 49.779 ms 49.835 ms 49.804 ms
5 192.168.xx.xx (192.168.xx.xx) 80.187 ms 80.426 ms 80.411 ms
6 192.168.xx.xx (192.168.xx.xx) 87.924 ms 88.178 ms 87.495 ms
7 192.168.xx.xx (192.168.xx.xx) 86.341 ms 87.290 ms 87.515 ms
8 100.64.xx.xx (100.64.xx.xx) 87.890 ms 87.557 ms 87.958 ms


On-premises endpoint device (Direct Connect, VMware Transit Connect or VPN) is using an endpoint IP address from subnet range. This is a reserved subnet for Carrier Grade Network Address Translation (NAT) per RFC 6598.

This block of addresses is specifically meant to be used by Internet Service Providers (or ISPs) that implement Carrier-Grade NAT, to connect their customer-premises equipment (CPE) to their core routers. For more information, see IPv4 Shared Address space  and tools.ietf.org/html/rfc6598., 4194304 Private network Shared address space[3] for communications between a service provider and its subscribers when using a carrier-grade NAT.


To resolve this issue, use the following guidelines/best practices:

  • Do not use the IP range addresses. They are always meant to be intermediary relay hops that are internal to the carrier networks.
  • VMC uses the same network and specification to implement CGN style networking between the VMC Edge routers in internal routing components which can create a conflict.
  • SDDCs that were created using version 1.10 or later have a smaller allocation of instead of the entire block. Address space other than the block can be used for endpoints.
  • SDDCs that were upgraded from releases prior to 1.10 do not reflect this change and will continue to have the allocation present.
  • VMC also uses this IP range between internal routing components it will create a conflict.
  • If a packet with either a source or a destination address in the 100.64 address space that conflicts with overlapping address space internal to the SDDC, it will be delivered inside the edge and will never egress.