Information Technology Reference
In-Depth Information
The enterprise has obtained ASN 300 and will multihome to AS 100 and AS 200. There are
two connections to AS 100—an OC-3 (155 Mbps) and a DS3 (45 Mbps). The OC-3 connects
to R1, and the DS3 connects to R2. There is a single DS3 to AS 200.
Tr affic Flow Requirements
The primary link for most traffic should be through the OC-3 on R1 to AS 100. The DS3
on R2 should be used only if the OC-3 on R1 is down. The DS3 to AS 200 should be used
for traffic local to AS 200, instead of traversing whatever peering, either direct or indirect,
might exist between AS 100 and AS 200.
Failure Scenarios
If the OC-3 fails, traffic should be distributed fairly even between both DS3s. Traffic should
be optimally routed to the degree that traffic destined for AS 200 is not sent to AS 100 and
vice versa.
If either DS3 fails, traffic should continue to be sent to the OC-3. The DS3 to AS 100 should
be used only if the OC-3 to AS 100 fails. If the DS3 to AS 200 fails, traffic should fail over
to the OC-3.
Initial Configurations
Table 6-1 shows the IP addressing used. Serial addressing refers to the OC-3 and DS3
interfaces. Loopback addressing is used for iBGP sessions. The address space used by the
enterprise is 172.160.0.0/16. The initial router configurations are provided in Examples 6-6,
6-7, and 6-8.
Table 6-1
Address Assignment for Enterprise Border Routers
Router Name
Remote Serial Address
Loopback Address
R1
100.100.100.2/30
172.160.1.1/32
R2
100.100.150.2/30
172.160.1.2/32
R3
200.200.200.2/30
172.160.1.3/32
Initial Configuration for R1
Example 6-6
R1#show running-config | begin bgp
router bgp 300
no synchronization
bgp log-neighbor-changes
network 172.160.0.0
continues
