Route Policy Options For An Eigrp Process - Cisco ASR 9000 Series Routing Configuration Manual

Implementing EIGRP

Route Policy Options for an EIGRP Process

Figure 15: Simple Hub-and-Spoke Network
The stub routing feature by itself does not prevent routes from being advertised to the remote router. In the
example in Figure 15: Simple Hub-and-Spoke Network, on page 310 , the remote router can access the
corporate network and the Internet through the distribution router only. Having a full route table on the remote
router, in this example, would serve no functional purpose because the path to the corporate network and the
Internet would always be through the distribution router. The larger route table would only reduce the amount
of memory required by the remote router. Bandwidth and memory can be conserved by summarizing and
filtering routes in the distribution router. The remote router need not receive routes that have been learned
from other networks because the remote router must send all nonlocal traffic, regardless of destination, to the
distribution router. If a true stub network is desired, the distribution router should be configured to send only
a default route to the remote router. The EIGRP Stub Routing feature does not automatically enable
summarization on the distribution router. In most cases, the network administrator needs to configure
summarization on the distribution routers.
Without the stub feature, even after the routes that are sent from the distribution router to the remote router
have been filtered or summarized, a problem might occur. If a route is lost somewhere in the corporate network,
EIGRP could send a query to the distribution router, which in turn sends a query to the remote router even if
routes are being summarized. If there is a problem communicating over the WAN link between the distribution
router and the remote router, an EIGRP stuck in active (SIA) condition could occur and cause instability
elsewhere in the network. The EIGRP Stub Routing feature allows a network administrator to prevent queries
from being sent to the remote router.
Route Policy Options for an EIGRP Process
Route policies comprise series of statements and expressions that are bracketed with the route-policy and
end-policy keywords. Rather than a collection of individual commands (one for each line), the statements
within a route policy have context relative to each other. Thus, instead of each line being an individual
command, each policy or set is an independent configuration object that can be used, entered, and manipulated
as a unit.
Each line of a policy configuration is a logical subunit. At least one new line must follow the then , else ,
and end-policy keywords. A new line must also follow the closing parenthesis of a parameter list and the
name string in a reference to an AS path set, community set, extended community set, or prefix set (in the
EIGRP context). At least one new line must precede the definition of a route policy or prefix set. A new line
must appear at the end of a logical unit of policy expression and may not appear anywhere else.
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
311