Chapter 16: Dynamic Routing Protocols
STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved. 459
BGP-4 supports Equal Cost Multi-Path (ECMP). In addition to being supported for eBGP, ECMP must be supported
when multiple next-hops exist for a prefix within an AS. This implies that ECMP is available for iBGP configurations. The
allowable range for ECMP is 1–4 routes. A value of 1 implies that ECMP is disabled.
BGP-4 supports Route Reflection. This is an alternative to full mesh iBGP. A route reflector is responsible for re-
advertising routes to an entire AS, but a route reflector client requires no additional functionality beyond the original
BGP specification.
BGP-4 supports the Communities Attribute. This allows similar routes to be grouped for the same policy treatment.
BGP-4 sends BGP Updates on card/port maintenance state changes. For example, if port maintenance indicates a state
change in a CAM subnet, this change triggers a BGP update to all peers indicating the reachability of the CAM-side
subnets.
BGP-4 supports Route-Refresh. This feature allows the C4/c CMTS to dynamically request a re-advertisement of the
Adj-RIB-Out from a BGP peer.
BGP-4 supports Capabilities Advertisement. This feature is required to advertise BGP capabilities to peers, such as
route refresh. When VPN extensions are available and two BGP speakers wish to exchange labeled VPN-IPv4 NLRI, they
must use BGP Capabilities Advertisement to ensure both peers are capable of processing such NLRI.
The C4/c CMTS, acting as a BGP Server, allows for a socket bind to any provisioned C4/c CMTS IP interface, including
loopback interfaces. For iBGP connections, loopback interfaces are the preferred IP address when establishing
connections since they represent the router itself and not any particular interface that is subject to state changes.
Additionally, the C4/c CMTS supports binding to a "wildcard" address. A "wildcard" address is assumed if the "update
source" parameter is not defined during the creation of a BGP instance.
BGP supports Route Reflector Client (RRC) and Confederation, but does not support peer groups or route filtering. In
the anticipated use of the C4/c CMTS as an RRC, there will be only a handful of routers north of the C4/c CMTS.
Therefore, the neighbor commands contain the IP addresses of the neighbors, but not of peer groups.
The C4/c CMTS supports BGP route filtering via route maps, which is required for C4/c CMTS peers with multiple ISPs
and is recommended in confederations. Without this filtering, the C4/c CMTS could advertise routes received from one
peer to another peer, becoming an unintentional transit router.
The C4/c CMTS permits system administrators to redistribute static, connected, RIP, or OSPF routes into BGP.
The C4/c CMTS supports BGP Route Aggregation.
Interior and Exterior BGP
The C4/c CMTS supports a full complement of features associated with Interior BGP (iBGP) and Exterior BGP (eBGP), with a
few noted exceptions.
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