Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 234)

210 Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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IP Traceroute over MPLS
1
The no option disables the ICMP MPLS response configuration. When the feature is disabled,
standard traceroute is used to trace a traffic path through an MPLS domain.
The output of the show ip traffic command displays counts for ICMP messages that have been
generated by an MPLS-enabled LSR with label extensions and returned to the source of the
traceroute probe. Refer to “
Displaying IP traffic statistics” for a description of the show ip traffic
command and associated output.
Use the show ip traffic command to verify the ICMP message count the user receives from the
traceroute output.
The show running configuration command has been modified to include the MPLS response
configuration.
NOTE
That the default configuration (mpls-response enabled and using IP routes) is not displayed in the
running configuration.
Prerequisites
• MPLS must be enabled on each of the provider LSRs. Refer to Chapter 38, “Configuring MPLS
Traffic Engineering” of the Multi-Service IronWare Multiprotocol Label Switch (MPLS)
Configuration Guide for more information.
• The user must enable TTL propagation on the ingress and egress LERs (PEs) before the user
can use the enhanced traceroute feature. TTL propagation ensures that the TTL value of the IP
packets received by the ingress LER is copied onto the outgoing MPLS label. Refer to
IP-over-MPLS TTL propagation control of the Multi-Service IronWare Multiprotocol Label Switch
(MPLS) Configuration Guide for more information.
Limitations
• The only ICMP messages supported with this feature are ttl-exceeded messages (Type 11).
Destination unreachable messages are not supported.
• IP Traceroute over MPLS requires Time-To-Live (TTL) propagation at the ingress and egress
Provider Edge (PE) routers. The feature is not applicable in contexts where TTL values are not
propagated (for example. in a Layer 2 VPN).
• IP Traceroute over MPLS supports a label stack size of up to five entries when displaying MPLS
label information in the traceroute output. For label stack sizes greater than five the traceroute
output only displays the first five label entries.
• The traceroute command cannot be used in a Layer 3 VPN network, when the ICMP response
is configured to use LSP and the egress router is a Brocade NetIron XMR or Brocade MLXe
series router running R05.2.00c or later. The Brocade NetIron CER and the Brocade NetIron
CES handles these cases correctly.
• The user cannot use the traceroute command in a Layer 3 VPN network when the ICMP
response is configured with the no use-lsp option. The transit LSRs have no Virtual Routing
and Forwarding (VRF) concept (only the PE routers do), and consequently no VPN routes when
the label-switching mechanism is blocked. Even when the responding LSR may have a route to
the traceroute source, the ICMP ttl-exceeded response packet generated by the LSR router
cannot be properly routed by the ingress router to the CE router because the response is a
normal IP packet and does not have a VPN label. Refer to
“Scenario B - Layer 3 VPN over
MPLS” for an illustration.
• IP Traceroute over MPLS is not backwards-compatible and is only supported on devices
running R05.2.00c and later.