Users Guide

Layer 3 Routing Commands 1249
• prefix-length —The length of the IPv6 prefix given as part of the ipv6-
prefix. This is required if a prefix is specified. A decimal value in the range
0 to 128 that indicates how many of the high-order contiguous bits of the
address comprise the prefix (the network portion of the address) in /length
format. A slash must precede the decimal value in /length format.
• as-set— If the as-set option is configured, the aggregate is advertised with
a non-empty AS_PATH. (Normally, the aggregate is advertised with an
empty AS path and the ATOMIC_AGGREGATE attribute.) If the
AS_PATH of all contained routes is the same, the AS_PATH of the
aggregate is the AS_PATH of the contained routes. Otherwise, if the
contained routes have different AS_PATHs, the AS_PATH attribute
includes an AS_SET with each of the AS numbers listed in the AS PATHs
of the aggregated routes. If the as-set option is not configured, the
aggregate is advertised with an empty AS_PATH.
• summary-only – When specified, the more-specific routes within the
aggregate address are not advertised to neighbors.
Default Configuration
No aggregate addresses are configured by default. Unless the options are
specified, the aggregate is advertised with the ATOMIC_AGGREGATE
attribute and an empty AS path, and the more specific routes are advertised
along with the aggregate.
Command Mode
• BGP Router Configuration mode
• IPv6 Address Family Configuration mode
User Guidelines
To be considered a match for an aggregate address, a prefix must be more
specific (i.e., have a longer prefix length) than the aggregate address. A prefix
whose prefix length equals the length of the aggregate address is not
considered a match.
When BGP originates a summary address, it installs a reject route in the
common routing table for the summary prefix. Any received packets that
match the summary prefix but not a more specific route match the reject
route and are dropped.