Chapter 50
| IP Routing Commands
Border Gateway Protocol (BGPv4)
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◆ WEIGHT – This attribute is used locally by a router to select a path when
multiple paths are available for a prefix.
◆ LOCAL_PREF – This local preference attribute is similar to that of the MED, but
within an AS. It sets a metric which is used between BGP speakers within an AS.
It can help in selecting an outgoing BGP when an AS has connectivity to
multiple ASes or multiple BGP routes even with the same next hop AS.
◆ ATOMIC_AGGREGATE – This attribute indicates that the routes were created by
aggregating more specific routes. More specific routes may exist for some the
these longer prefixes, but the router chose not to send them, so as to reduce
the size for the AS path parameters.
◆ AGGRATOR – This is an optional attribute that identifies the AS and router that
originally aggregated the routes.
◆ COMMUNITY – This attribute associates routing information with a community
of users. These communities share a common property, and tagging routes
with a community makes it easier for routers to identify that property and
enforce appropriate routing policies.
◆ ORIGINATOR_ID – This attribute is included when a route reflector reflects a
route. Then if the reflector later receives a route with its own originator ID, a
potential routing loop can be broken.
◆ CLUSTER_LIST – This attribute is of a list of the clusters through which a route
has been reflected. Every route reflector adds its own cluster ID to the list. If the
reflector receives a route with its own cluster ID, a potential routing loop can be
broken.
◆ MP_REACH_NLRI – This attribute describes routes for network protocols other
than IPv4. The attribute identifies the protocol with an address family identifier
(AFI) and a subsequent address family identifier (SAFI). It contains the address
of the next hop router for the destinations, as well as the link level (e.g.,
Ethernet) addresses for that next hop. It concludes with the destinations
expressed as prefixes.
◆ MP_UNREACH_NLRI – This attribute withdraws non-IPv4 routes. It includes the
route’s AFI, SAFI, and network address prefixes.
◆ EXTENDED-COMMUNITIES – This attribute provides a mechanism for labeling
various information carried in route advertisements. It provides an extended
type field to ensure that communities can be assigned for a broad range of
uses, without fear of overlap.
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