Information Technology Reference
In-Depth Information
The design options for a multihomed stub network are using a single border router for the
enterprise edge and using multiple routers. These design scenarios are described in detail
in the following sections.
Single Border Router
The single border router design scenario, shown in Figure 6-2, involves the use of a single
router at the enterprise border, with multiple connections to the same provider. These con-
nections are terminated at the provider in diverse locations.
Figure 6-2
Stub Multihomed Single Border Router Architecture
Provider A (AS 100)
Enterprise (AS 65100)
When this design is deployed, BGP should be used to provide additional control for possi-
ble load sharing. The use of a single upstream provider allows for the use of a private AS.
This means that the enterprise does not need to obtain a unique and publicly visible ASN
from its regional registry. The upstream provider can remove the private ASN from the
updates.
The use of BGP in this design can give the enterprise a greater degree of influence over the
inbound traffic patterns and better control over its outbound traffic flow. This can be espe-
cially useful if the links are unequally sized, where routing policy can be used to obtain load
sharing in proportion to the links' size.
Multiple Border Routers
The use of a single enterprise border router leads to a single point of failure. The addition
of one or more border routers removes the last single point of failure. This design option