JN0-1300: Data Center Design, Specialist (JNCDS-DC)

Multimode fiber provides an appropriate high-performance, lower-initial-cost medium for inter-rack 10GbE and 40GbE links at this distance when paired with suitable optics. Cisco documents 40GBASE-CSR support for up to 300 m on OM3 multimode fiber and 400 m on OM4. Direct-attach copper (DAC) is a short-reach, low-cost connection well suited to devices within the same rack; it does not support the dispersed, up-to-300-meter inter-rack connections.

In a Junos Fusion architecture, the cascade ports on the aggregation device that connect to satellite devices use IEEE 802.1BR (Bridge Port Extension) encapsulation. IEEE 802.1BR adds an E-Tag to frames traversing the cascade link, identifying the specific extended (satellite) port the frame is associated with, which allows the aggregation device to manage the satellite device's ports as if they were local interfaces.

EBGP advertisements use the advertising router as the next hop by default, so routes exchanged across directly connected spine-to-leaf links have a reachable next hop without the additional next-hop resolution typically needed for IBGP-learned routes.

When unsupported devices sit along an application's path, the Cloud Analytics Engine still includes them in the topology but can only pull their IP address and hop number from basic path discovery; devices it does support, such as QFX Series and EX Series switches, continue to supply enriched per-hop telemetry beyond that minimal information.

BGP confederations divide an autonomous system into sub-ASs, reducing the IBGP full-mesh scaling requirement. Route reflectors can advertise routes learned from IBGP clients to other IBGP peers, eliminating the need for every IBGP router to peer with every other router. BGP communities and AS-path prepending influence routing policy or path selection but do not remove the IBGP mesh requirement.