Information Technology Reference
In-Depth Information
the Internet resource must be announced to the internal network to provide routing infor-
mation for reaching Internet destinations. Internet connectivity is provided in Location A
and Location C. The public Internet DMZ is located outside firewalls.
In Location A, R13 connects to the firewall, which leads to the external DMZ. In Location C,
R14 connects to a firewall, which leads to the other external DMZ. The network core will
announce full internal routing information via eBGP to routers R13 and R12. Routers R13
and R12 originate the default route into the network core, which is disseminated to the
major centers and remote site aggregation autonomous systems. The routers R13 and R12
have default routes pointing toward the firewalls to provide full reachability.
The same AS is used for both Internet connectivity sites even though there is no iBGP
session between R12 and R13. Usually, it is unacceptable to have multiple BGP routers in
the same AS that are not connected via iBGP. However, in this scenario, they act as a stub
AS. They do not require connectivity to each other. There is no reason for R12 to ever send
traffic to R13, and vice versa.
Migration Plan
The migration plan is designed to first provide the supporting infrastructure that will be
needed for the BGP sessions. The BGP portion will then be overlaid on the network, allow-
ing verification of proper prefix propagation. The EIGRP adjacencies between the border
routers and the core routers will then be broken, allowing the BGP-learned prefixes to take
effect. The EIGRP core process should then be renumbered to prevent misconfiguration,
leading to accidental reformation of EIGRP adjacencies between the border routers and the
core routers. The migration plan is designed to allow for deployment of a BGP core with
minimal impact on the network's normal operation.
Supporting Infrastructure
The supporting infrastructure involves creating the loopback interfaces. The loopback
address on each router will also serve as the router ID. The loopback interfaces are first
configured according to a predefined scheme and are then included in the EIGRP routing
process. The 172.16.0.0/16 address space will be used for the loopback addressing to
provide easy identification of loopback addresses when examining the routing table. The
loopback addressing scheme is 172.16.X.1/24, where X is the router number.
Table 5-3 shows the addressing that will be used.
