Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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IP Traceroute over MPLS
1
1. Re-enable the MPLS response default configuration on each LSR (R1, R2, R3, and R4).
Brocade# configure terminal
Brocade(config)# ip icmp mpls-response
2. On 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
In this scenario, only PE1 and CE2 return traceroute information. ICMP error messages generated
at R2, R3, and PE2 with subsequent probes are dropped, because these LSRs can only use
label-switching to transport the ICMP response and use-lsp is disabled in the ICMP response
default configuration. Traceroute prints an asterisk (*) for each dropped package. The fifth
traceroute probe makes it to CE2, which routes an ICMP destination unreachable message back to
CE1 using IP routing table lookup. Refer to
for more information.
Tracing a route across an MPLS domain with label extensions using LSP
Assumptions: The default MPLS response feature is enabled on all provider routers. The user
intends to trace the LSPs in the MPLS core and the user configures the routers to use LSPs. CE1 is
sending a traceroute to CE2 with a destination IP address of 10.1.3.8. ICMP messages are
generated with label stack extensions (always enabled unless explicitly disabled) and are
propagated along configured LSPs. Only the PE routers have specific IP routes to the CE routers.
Scenario A - IP over MPLS
IP over MPLS (IPoMPLS) is enabled in the provider core.
1. Issue the ip icmp mpls-response command with the use-lsp option on each LSR (R1, R2, R3,
and R4).
Brocade# configure terminal
Brocade(config)# ip icmp mpls-response use-lsp
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 <1 ms <1 ms <1 ms 10.56.1.2
MPLS Label=1048 Exp=7 TTL=1 S=1
3 <1 ms <1 ms <1 ms 10.52.10.4
MPLS Label=1026 Exp=7 TTL=1 S=1
4 <1 ms <1 ms <1 ms 10.34.22.8
5 <1 ms <1 ms <1 ms 10.1.3.8
IP forwarding is enabled in the MPLS domain and the ICMP responses are forwarded using IP
routes. Traceroute reports MPLS labels at hop 2 and 3 but no VPN label.