Operation Manual – MPLS Basics
H3C S9500 Series Routing Switches
Chapter 1 MPLS Basics Configuration
1-28
1.9 Configuring MPLS IP TTL Processing
1.9.1 Configuration Prerequisites
Before configuring MPLS IP TTL propagation, be sure to complete this task:
z
Configuring MPLS basic capability
1.9.2 Configuring MPLS IP TTL Propagation
Follow these steps to configure IP TTL propagation of MPLS:
To do…
Use the command…
Remarks
Enter system view
system-view
—
Enter MPLS view
mpls
Required
Enable MPLS IP TTL
propagation for either
public network packets or
VPN packets
ttl propagate
{
public
|
vpn
}
Optional
Enabled for only public
network packets by
default
Caution:
z
The
ttl propagate
command affects only the propagation of the IP TTL to the MPLS
label. At the egress, the system uses the smaller one between the IP TTL and MPLS
TTL as the TTL of the IP packet and decrements the value by 1.
z
If you want to enable MPLS IP TTL propagation for VPN packets on one LSR, you
are recommended to do so on related PEs, guaranteeing that you can get the same
result when tracerting from those PEs.
1.9.3 Specifying the Type of Path for ICMP Responses
ICMP responses can use two kinds of paths: IP route and LSP.
For MPLS packets with one-level labels, you can configure MPLS to send back ICMP
responses along IP routes instead of LSPs when the TTL expires.
In MPLS, an IP router generally maintains public network routes only, and MPLS
packets with one-level labels carry public network payload. Therefore, you can
configure this function.
In MPLS VPN, for ASBRs and SPEs in HoVPN applications (including SPEs in
applications), MPLS packets that carry VPN packets may have one-level labels. To
view the forwarding path of VPN packets on public networks through
tracert
, you must:
