Cisco NCS 5500 Series

Selective FIB Download
The NCS 5500 system supports LOW-FIB scale and HIGH-FIB scale (with external TCAM) line cards. The
Selective FIB Download feature enables the combination of both these cards to be used in the same chassis.
The Selective FIB Download feature permits filtering of routes on the LOW-FIB scale line cards. The filtering
of routes is achieved by marking the routes “external-reach” using a BGP route policy. The match criteria used
within the BGP policy are prefix values, community, as-path, next-hop, local-pref, MED, and so on.
This feature helps to maximize resources available and to improve routing scalability.
Functionality
By default, all routes are marked “internal-reach”. However, using a BGP route policy, users can classify the
BGP routes “external-reach”.
The “external-reach” routes are programmed only in the HIGH-FIB scale line card, while internal routes (for
example-IGP, external, connected, static, and BGP routes that are not marked “external”) are programmed in
both HIGH-FIB and LOW-FIB scale line cards. Because the “external-reach” routes are not programmed in
the LOW-FIB scale line card, we recommend that you do not to mix bundle members from the LOW-FIB
Scale and HIGH-FIB scale line cards under the same bundle interface.
Content Server Access
In this scenario, a content server is connected to the HIGH-FIB scale line card and the core uplink network
is hosted on the LOW-FIB scale line card:
•
Traffic originating from the content server requires global address reachability. Therefore, the global
internet routes and the internal network routes are programmed in the HIGH-FIB line card.
•
The core uplink network that is hosted on the LOW-FIB scale line card requires reachability only to the
internal network. Therefore, the global internet routes are not programmed in the hardware of the
LOW-FIB scale line card.
•
MPLS labels are programmed on both the HIGH-FIB scale and LOW-FIB scale line cards.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
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Implementing BGP
Selective FIB Download