Extreme Networks BlackDiamond 6800 MPLS Installation And User Manual page 130

Configuring MPLS Layer-2 VPNs
on the user VLAN ensures that only one LSR (the ESRP master) forwards traffic for the
VLAN at each site.
The redundant IP address configured on the tunnel endpoint VLAN (IP ) is also used
T1
as the tunnel endpoint address in the same manner as described for the preceding
example. Therefore, it is the ESRP master for the user VLAN that forwards traffic onto
the tunnel LSP, and it is the ESRP master for the tunnel endpoint VLAN that forwards
traffic received from the tunnel LSP (as a consequence of being the LSR with which the
tunnel LSP is established).
The tunnel endpoint VLANs are created specifically to provide fault-tolerant tunnel
endpoint IP addresses in a manner that is totally transparent to the user VLAN. ESRP is
used to provide the fault-tolerant IP addresses. The tunnel endpoint IP addresses could
be defined on the user VLAN instead. However, an OSPF route must be advertised for
a tunnel endpoint IP address to ensure that the underlying LSP is established by LDP.
By creating the tunnel endpoint VLAN the IP address defined on the user VLAN does
not need to be exported into the MPLS backbone (which would expose information
about the user VLAN to the MPLS backbone).
IP addresses are defined on the user VLAN (IP ) for ESRP purposes, but these
U1
addresses are only used locally at each site. In this example, IP addresses would have to
be defined on a different set of VLANs to provide the connectivity to the MPLS
backbone. These MPLS VLANs are not depicted in Figure 7-6. The MPLS VLANs
contain a different set of physical ports than the user VLAN, and MPLS must be
enabled on the MPLS VLANs.
ESRP standby LSRs preestablish tunnel LSPs to the ESRP master LSR at the other site.
The pre-established tunnel LSPs are inactive as long as the LSR is in standby mode, but
can expedite recovery from a failure. For example, if LSR A were to fail, LSR B would
become the ESRP master at Site 1, and LSR B would already have an LSP established to
LSR C. Upon becoming ESRP master, LSR B would advertise an OSPF route and a
MPLS label mapping for IP , and LSR C would then begin using the new tunnel LSP to
T1
LSR B.
The ESRP route table tracking feature is also useful in conjunction with TLS. ESRP route
table tracking can be configured to initiate an ESRP failover when no route is available
to the tunnel endpoint IP address. For example, LSR A can be configured to initiate a
failover to LSR B when its route table does not have an entry for IP . Each of the LSRs
T2
would be configured to use ESRP route table tracking in a similar manner.
7-20 MPLS Module Installation and User Guide