The following rules determine how the router sets the Ethertype field value of the outgoing packet:
If the swapped label is not the Bottom-of-Stack label, the Ethertype is set to the MPLS value.
If the swapped label is the Bottom-of-Stack label and the outgoing label is not implicit-null, the Ethertype is set to the MPLS value.
If the swapped label is the Bottom-of-Stack label and the outgoing label is implicit-null, the Ethertype is set to the IPv4 or IPv6 value when the first nibble of the exposed IP packet is 4 or 6 respectively.
The router sets the TTL of the outgoing packet as follows:
The TTL of a forwarded IP packet is set to MIN(MPLS_TTL-1, IP_TTL), where MPLS_TTL refers to the TTL in the outermost label in the popped stack and IP_TTL refers to the TTL in the exposed IP header.
The TTL of a forwarded MPLS packet is set to MIN(MPLS_TTL-1, INNER_MPLS_TTL), where MPLS_TTL refers to the TTL in the outermost label in the popped stack and INNER_MPLS_TTL refers to the TTL in the exposed label.