Configuring Mpls Fast Forwarding - 3Com MSR 50 Series Configuration Manual

Configuring MPLS Fast
Forwarding
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:
Configure the ttl propagate vpn command on all the related PEs to allow IP
■
TTL propagation of VPN packets.
Configure the undo ttl expiration pop command on the ASBRs and SPEs to
■
assure that ICMP responses can be transported back through the original LSPs.
n
SPE refers to the superstratum PE or service provider-end PE.
■
For details about HoVPN, refer to
■
Follow these steps to configure the path for ICMP responses:
To do...
Enter system view
Enter MPLS view
Specify that the ICMP response be
transported back along the IP route
when the TTL of an MPLS packet
expires
Specify that the ICMP response be
transported back along the LSP
when the TTL of an MPLS packet
expires
MPLS fast forwarding is designed to improve MPLS forwarding efficiency. With
MPLS fast forwarding, the first packet of a data stream is forwarded based on the
normal MPLS forwarding process, during which period the fast forwarding feature
records in the fast forwarding cache a fast forwarding entry including the link layer
header for the packet. All subsequent packets of the data stream are then
forwarded based on the fast forwarding entry, using the link layer header for the
first packet. This greatly improves MPLS forwarding efficiency.
MPLS fast forwarding depends on IP fast forwarding; it works when IP fast
forwarding is enabled, and stops working when IP fast forwarding is disabled.
n
For information about IP fast forwarding, refer to
on page 653.
Table 50 Follow these steps to configure MPLS fast forwarding:
To do...
Enter system view
Enter interface view

Configuring MPLS Fast Forwarding

"Configuring HoVPN" on page
Use the command...
system-view
mpls
ttl expiration pop
undo ttl expiration pop
"Fast Forwarding Configuration"
Use the command...
system-view
interface interface-type
interface-number
1335
1495.
Remarks
-
-
Optional. Use either
command.
By default, the ICMP
response message of an
MPLS packet with a
one-level label is
transported back along
the IP route.
Remarks
-
-