Traffic Leaking To Grt - Alcatel-Lucent 7750 SR Manual

Virtual Private Routed Network Services

Traffic Leaking to GRT

Traffic leaking to Global Route Table (GRT) allows service providers to offer VPRN and Internet
services to their customers over a single VRF interface. This currently supports IPv4 services and
requires the customer VRPN interfaces to terminate on a minimum of IOM3-XP and IMM
hardware. It is also supported on the 7750 SR-C12.
Packets entering a local VRF interface can have route processing results derived from the VPRN
forwarding table or the GRT. The leaking and preferred lookup results are configured on a per
VPRN basis. Configuration options can be general (for example, any lookup miss in the VRPN
forwarding table can be resolved in the GRT), or specific (for example, specific route(s) should
only be looked up in the GRT and ignored in the VPRN). In order to provide operational
simplicity and improve streamlining, the CLI configuration is all contained within the context of
the VPRN service.
This feature is enabled within the VPRN service context under config>service>vprn>grt-lookup.
This is an administrative context and provides the container under which all specific commands
can be entered, except for policy definition. Policy definitions remain unchanged but are
referenced from this context.
The "enable-grt" command establishes the basic functionality. When it is configured, any lookup
miss in the VRF table will be resolved in the GRT, if available. By itself, this only provides part of
the solution. Packet forwarding within GRT must understand how to route packets back to the
proper node and to the specific VPRN from which the destination exists. Destination prefixes
must be leaked from the VPRN to the GRT through the use of policy. Policies are created under
the config>router>policy-options hierarchy. By default, the number of prefixes leaked from the
VPRN to the GRT is limited to five. The export-limit command under the grt-lookup hierarchy
allows the service provider to override the default, or remove the limit.
When a VPRN forwarding table consists of a default route or an aggregate route, the customer
may require the service provider to poke holes in those, or provide more specific route resolution
in the GRT. In this case, the service provider may configure a "static-route", under the "enable-
grt" context. The lookup result will prefer any successful lookup in the GRT that is equal to or
more specific than the static route, bypassing any successful lookup in the local VPRN.
This feature and Unicast Reverse Path Forwarding (uRPF) are mutually exclusive. When a VPRN
service is configured with either of these functions, the other cannot be enabled. Also, prefixes
leaked from any VPRN should never conflict with prefixes leaked from any other VPRN or
existing prefixes in the GRT. Prefixes should be globally unique with the service provider network
and if these are propagated outside of a single providers network, they must be from the public IP
space and globally unique. Network Address Translation (NAT) is not supported as part of this
feature.
7750 SR OS Services Guide Page 1095