| encapsulation-limit | uint32 | 0 | How many additional levels of encapsulation are permitted to be prepended to packets. This property applies only to IPv6 tunnels. To disable this option, add NM_IP_TUNNEL_FLAG_IP6_IGN_ENCAP_LIMIT (0x1) to ip-tunnel flags. | 
| flags | uint32 | 0 | Tunnel flags. Currently, the following values are supported: NM_IP_TUNNEL_FLAG_IP6_IGN_ENCAP_LIMIT (0x1), NM_IP_TUNNEL_FLAG_IP6_USE_ORIG_TCLASS (0x2), NM_IP_TUNNEL_FLAG_IP6_USE_ORIG_FLOWLABEL (0x4), NM_IP_TUNNEL_FLAG_IP6_MIP6_DEV (0x8), NM_IP_TUNNEL_FLAG_IP6_RCV_DSCP_COPY (0x10), NM_IP_TUNNEL_FLAG_IP6_USE_ORIG_FWMARK (0x20). They are valid only for IPv6 tunnels. | 
| flow-label | uint32 | 0 | The flow label to assign to tunnel packets. This property applies only to IPv6 tunnels. | 
| fwmark | uint32 | 0 | The fwmark value to assign to tunnel packets. This property can be set to a non zero value only on VTI and VTI6 tunnels. | 
| input-key | string |  | The key used for tunnel input packets; the property is valid only for certain tunnel modes (GRE, IP6GRE). If empty, no key is used. | 
| local | string |  | The local endpoint of the tunnel; the value can be empty, otherwise it must contain an IPv4 or IPv6 address. | 
| mode | uint32 | 0 | The tunneling mode, for example NM_IP_TUNNEL_MODE_IPIP (1) or NM_IP_TUNNEL_MODE_GRE (2). | 
| mtu | uint32 | 0 | If non-zero, only transmit packets of the specified size or smaller, breaking larger packets up into multiple fragments. | 
| output-key | string |  | The key used for tunnel output packets; the property is valid only for certain tunnel modes (GRE, IP6GRE). If empty, no key is used. | 
| parent | string |  | If given, specifies the parent interface name or parent connection UUID the new device will be bound to so that tunneled packets will only be routed via that interface. | 
| path-mtu-discovery | boolean | TRUE | Whether to enable Path MTU Discovery on this tunnel. | 
| remote | string |  | The remote endpoint of the tunnel; the value must contain an IPv4 or IPv6 address. | 
| tos | uint32 | 0 | The type of service (IPv4) or traffic class (IPv6) field to be set on tunneled packets. | 
| ttl | uint32 | 0 | The TTL to assign to tunneled packets. 0 is a special value meaning that packets inherit the TTL value. |