Riverstone Networks WICT1-12 - Manual (Page 345)

Riverstone Networks RS Switch Router User Guide Release 8.0 17-37
MPLS Configuration Configuring L3 Label Switched Paths
Standby
The secondary path is an alternate path to a destination and is only used if the primary path can no longer reach the
destination. If the LSP switches from the primary to the secondary path, it will revert back to the primary when it
becomes available. The switch from the primary to the secondary path can take awhile as timeouts and retries need to
be exhausted. You can specify that the secondary path be placed into a “hot” standby state to allow faster cutover from
the primary to the secondary path in the event of problems with link connectivity. Specify the
standby
parameter
when configuring the secondary path. Note that if paths are placed into hot standby state, all LSRs in the LSP must
maintain this state information.
Policies
On the RS, you can optionally create and apply a policy to specify the type of traffic allowed on the path. On the RS,
a policy is a definition of the type of traffic to which a particular router feature is applied. For example, you can create
policies that define traffic from a particular source address to a particular destination address, or traffic of a certain
protocol type.
For MPLS, you can create a policy that defines traffic characteristics such as source/destination IP addresses and
netmask values, source/destination MAC addresses, VLAN ID, 802.1p priority, and protocol type. You can then apply
the policy to an LSP. Only the labeled packets that meet the requirements of the policy are allowed to travel on that
LSP. For example, you can define a policy that allows only labeled packets with source IP addresses in the 100.1.1.0/24
network to traverse an LSP.
On the RS, use the
mpls create policy
command to create policies that you can apply to LSPs. For example, the
following command creates a policy that will allow only labeled traffic with the source IP address 100.1.1.0/24:
You can then use the
mpls set static-path
or
mpls set label-switched-path
commands to apply the policy
to a previously-created LSP.
Note that an MPLS policy affects the traffic that is forwarded on an LSP. If you want to restrict the establishment of
LSPs by restricting the label requests and label bindings that are distributed, use LDP filters. For more information,
see
Section 17.4.6, "Using LDP Filters."
Dynamic L3 LSP Configuration Example
Figure 17-9 shows a network where RS router R5 is the ingress router for a dynamic LSP to the egress router R7. The
LSP configuration consists of two different path designations: the primary path is an explicit path from R5 to R7, while
the secondary path is an explicit path that follows specific hops from R5 to R6 and then to R7. The secondary path also
mpls create policy allow_subnet_100 src-ipaddr-mask 100.1.1.0/24
mpls set static-path to_SanJose policy allow_subnet_100