Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 239)

Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide 215
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MPLS LDP-IGP synchronization
1
This example is included only to illustrate the CLI behavior. It is not useful for diagnosing LSP
routing problems. Regardless of whether the user has IP over MPLS or a Layer 3 VPN configured,
the provider transit router cannot propagate ICMP errors without label extensions when use-lsp is
specified. For this reason, traceroute returns information only for the PE1 and CE2.
1. Issue the ip icmp mpls-response command with the use-lsp and the no-label-extension options
on each LSR (R1, R2, R3, and R4).
Brocade# configure terminal
Brocade(config)# ip icmp mpls-response use-lsp no-label-extension
2. On the CE 1 (IP address 10.3.3.3), issue the traceroute command with the destination address
of CE2 (IP address 10.1.3.8).
CE1# traceroute 10.1.3.8
Type Control-c to abort
Tracing the route to IP node (10.1.3.8) from 1 to 30 hops
1 <1 ms <1 ms <1 ms 10.51.3.7
2 * * * ?
3 * * * ?
4 * * * ?
5 <1 ms <1 ms <1 ms 10.1.3.8
Understanding traceroute label information
When IP traceroute over MPLS is enabled on a provider LSR and configured to use label extensions,
the traceroute command displays label information in its output.
Table 13 explains the output from the enhanced traceroute command.
TABLE 13 Output from the enhanced traceroute command
This Field... Displays...
MPLS Label The label appended to the ICMP ttl-exceeded message by the LSR that
generated the message at the specified hop. The label is a 20-bit value.
Exp A field in the MPLS label for experimental use. The field is a 3-bit value
TTL Time-to-live value of the datagram when it arrived at the LSR that generated
the ICMP message. The TTL field is an 8-bit value.
S Indicates the position of the label in the label stack The S field is a 1-bit value.
A label with S=1 is located at the bottom of the stack. A label with a value of
S=0 is not at the bottom of the stack.
MPLS LDP-IGP synchronization
Packet loss can occur because the actions of the IGP and LDP are not synchronized.
The MPLS LDP-IGP Synchronization feature provides the following benefits:
• Provides a means to synchronize LDP and IGPs to minimize MPLS packet loss.
• MPLS LDP-IGP Synchronization may be enabled per interface, or globally
• OSPF and IS-IS are supported for the IGP; each operates independently