9
As a best practice, set the same TTL processing mode on all LSRs of an LSP.
•
To enable TTL propagation for a VPN, you must enable it on all PE devices in the VPN. Then,
you can get the same traceroute result (hop count) from those PEs.
To enable TTL propagation:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enable TTL
propagation.
mpls ttl propagate
{
public
|
vpn
}
By default, TTL propagation is enabled for
public network packets and is disabled for
VPN packets.
This command affects only the propagation
between IP TTL and label TTL. Within an
MPLS network, TTL is always copied
between the labels of an MPLS packet.
20B
Enabling sending MPLS TTL-expired messages
This feature enables an LSR to generate an ICMP TTL-expired message upon receiving an MPLS
packet with a TTL of 1. If the MPLS packet has only one label, the LSR sends the ICMP TTL-expired
message back to the source through IP routing. If the MPLS packet has multiple labels, the LSR
sends it along the LSP to the egress node, which then sends the message back to the source.
To enable sending MPLS TTL-expired messages:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enable sending MPLS
TTL-expired messages.
mpls ttl expiration enable
By default, this feature is enabled.
21B
Enabling MPLS forwarding statistics
MPLS label forwarding for LSPs forwards a labeled packet based on its incoming label.
Perform this task to enable MPLS label forwarding statistics for LSPs and set the statistics collection
interval. Then, you can use the
display mpls lsp verbose
command to view MPLS label statistics.
If you execute the
mpls statistics
enable
command for a VPN instance, MPLS label forwarding
statistics is enabled for all LSPs in that VPN instance. For more information about enabling MPLS
label forwarding statistics for a VPN instance, see "
667H
Configuring MPLS L3VPN
."
To enable MPLS label forwarding statistics for LSPs:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enable MPLS label
forwarding statistics for the
specified LSPs.
mpls statistics
{
all
| [
vpn-instance
vpn-instance-name
] {
ipv4
ipv4-address mask-length
|
ipv6
ipv6-address prefix-length
} |
static
|
te ingress-lsr-id tunnel-id
}
By default, MPLS label
forwarding statistics is disabled
for all LSPs.
3.
Set the MPLS label
forwarding statistics
collection interval.
mpls statistics interval
interval
By default, the MPLS label
forwarding statistics collection
interval is not set.