Information Technology Reference
In-Depth Information
Major Center Attachment
This network has three major centers, each in its own BGP AS. The BGP autonomous
systems for the major centers are AS65101, AS65102, and AS65103. The major centers
connect to the BGP core through eBGP sessions. Each major center runs its own EIGRP
process, with connectivity external to the center provided by the network core. The border
routers for AS65101 are R1 and R2. The border routers for AS65102 are R7 and R8. The
border router for AS65103 is R9. The BGP peering sessions between the major center
border routers and the core are sourced from the physical link addresses of the Ethernet
DMZ. When there are multiple border routers in a major center, they are connected with
iBGP sourced from the loopback interfaces with
next-hop-self
configured for the iBGP
sessions.
Remote Site Aggregation
This network has approximately 400 remote site routers. The remote sites are dual-homed
via Frame Relay PVCs to hub routers in different major centers for redundancy. The hub
routers are not part of the major center BGP or EIGRP routing processes. The BGP and IGP
design for the remote site aggregation is based on the earlier discussion of remote site
connectivity.
The hub routers, which are physically located in Location A and Location C, connect via
eBGP to the physically colocated core routers. This means that R3 is eBGP peered with
router R4 and R11 is eBGP peered with R10. The hub routers are not iBGP peered because
there is no direct connectivity between them except through the remote sites. To scale the
remote site EIGRP process, only the default route is advertised via EIGRP to the remote
site router. The only prefixes advertised by a remote site router are the prefixes at that
remote site.
The bandwidth from each remote site to the hub routers might vary, which is common when
the dual PVCs are designed to act as a primary PVC and secondary PVC. The hub routers
will redistribute routes directly from EIGRP into BGP and will set the MED outbound for
the prefixes to the IGP metric for that prefix. This provides the core with information about
which PVC is preferred as the primary path and allows remote sites to have primary
connectivity to either R3 or R11.
The default route will be injected into EIGRP from BGP. The redistribution into EIGRP
will be filtered to allow only the default route. The redistribution from EIGRP into BGP will
be filtered to block the default route.
Internet Connectivity
The actual Internet connections to the provider's network are terminated on routers that are
not shown. The internal network design is separate from the Internet connectivity. However,
