SRv6: TTL propagation for SRv6 tunnels

We have enabled time-to-live (TTL) or hop limit (HL) propagation for SRv6 tunnels to allow traceroute probe packets generated by customer edge (CE) node to have TTL or HL expiry on SRv6 tunnels. TTL propagation is enabled by default from IP or MPLS to SRv6 (on encapsulation) and SRv6 to IP or MPLS (on de-encapsulation), ensuring traceroute visibility. The TTL or HL is propagated during encapsulation and de-encapsulation between the payload (IPv4, IPv6, or MPLS header) and SRv6 (outer IPv6) header. When a TTL or HL expiration occurs, the transit router generates an ICMP error message and encapsulates it within the SRv6 tunnel. The egress node subsequently de-encapsulates the packet and returns the ICMP error message to the originating source. To disable TTL propagation, use the no-propagate-ttl statement at the [edit routing-options source-packet-routing srv6] hierarchy level.

To enable tunneling ICMP error messages on transit routers include the icmp-tunneling statement at the [edit routing-options source-packet-routing srv6] hierarchy level to generate and encapsulate ICMP error packets through the SRv6 path.