Technical data

6 Brocade MLX Series and NetIron Family Documentation Updates

53-1002805-03

IPv6 Traceroute over an MPLS network

Tracing an IPv6 route through an MPLS domain

Figure 1 shows an MPLS-enabled provider network consisting of four LSRs. PE1 is the ingress PE

Label Edge Router (LER), P1 and P2 are transit LSRs, and PE2 is the egress provider edge LER. CE1

and CE2 are CE devices located in different geographical locations.

FIGURE 1 IPv6 Traceroute in an MPLS cloud

To understand the IPv6 traceroute behavior in an MPLS domain, assume the following:

• Customer traffic is tunneled through a MPLS VPN network, and traffic within the MPLS core is

forwarded by label-switching only.

• The CE1 router sends UDP packets from CE1 router towards the CE2 router.

• Traceroute is configured to generate ICMPv6 messages per ICMP extensions and to use LSPs

to forward these messages. Refer to “Configuring IPv6 Traceroute over MPLS” on page 8 for

more information.

• The PE routers are aware of the source and destination IPv6 addresses while the transit LSRs

have no such knowledge.

• The traceroute command is issued from CE1 to CE2 and reports the following information:

Brocade# traceroute ipv6 2001:DB8:2::2

Type Control-c to abort

Tracing the route to IPv6 node 2001:DB8:2::2 from 1 to 30 hops

1 <1 ms <1 ms <1 ms 2001:DB8:1::2

2 <1 ms <1 ms <1 ms 2001:DC8:200::3

MPLS Label=1026 Exp=0 TTL=1 S=0

MPLS Label=794624 Exp=0 TTL=1 S=1

3 <1 ms <1 ms <1 ms 2001:DD8:300::2

MPLS Label=1029 Exp=0 TTL=1 S=0

MPLS Label=794624 Exp=0 TTL=2 S=1

4 <1 ms <1 ms <1 ms 2001:DE8:300::2

5 <1 ms <1 ms <1 ms 2001:DB8:2::2

NOTE

The traceroute output reports information on a traceroute packet only when its TTL equals 1. Label

stack information associated with subsequent routing of the ICMP message along the LSPs to the

destination and back to the source is not displayed.

In the Figure 1 scenario, the traceroute operation can be described as follows:

P2 PE2 CE2P1

MPLS/IPv4 cloud

PE1CE1

2001:DC8:200::3 2001:DB8:2::22001:DC8:200::3 2001:DD8:300::2 2001:DE8:300::22001:DB8:1::2