3Com S7906E - Switch, Руководство по настройке

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Configuring MPLS IP TTL Processing
Configuration Prerequisites
Before configuring MPLS IP TTL propagation, be sure to complete this task:
z
Configuring MPLS basic capability.
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
ttl propagate
{
public
|
vpn
}
Optional
Enabled for only public
network packets by default
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The
ttl propagate
command affects only the propagation of the IP TTL to the TTL in an MPLS label.
At 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.
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If you enable MPLS IP TTL propagation for VPN packets on one LSR, you are recommended to do
so on all related PEs as well, guaranteeing that you can get the same result when tracerting from
those PEs.
z
Some VPN packets carry two layers of labels, outer and inner, for transmission in the public
network and private network respectively. The LSQ1SRP1CB engine and EA series LPUs have to
copy the IP TTL of private network packets to the inner label before they can copy the IP TTL to the
outer label. However, SD series and EB series can copy the IP TTL of private packets to the outer
label directly.
Specifying the Type of the Paths for ICMP Responses
ICMP responses can use two kinds of paths: IP route and LSP.
For MPLS packets with one-level of 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
of labels carry public network payload. Therefore, you can configure this function.
In MPLS VPN, for autonomous system border routers (ASBRs) and SPEs in Hierarchy of VPN (HoVPN)
applications (including SPEs in applications with recursions), MPLS packets that carry VPN packets
may have only one-level of labels. To tracert the VPN packets on public networks in this case, you need
to: