Prefix Lists

Prefix lists are used to specify an address or range of addresses to be permitted or denied in route updates. The BGP routing protocol uses prefix lists for IPv4. All IPv6 routing protocols can use prefix lists when exchanging IPv6 addresses between protocols or when filtering updates.

Prefix lists are named lists. An entry in the list permits or denies an address or range of addresses, as in Example B-20.

Example B-20. Prefix lists permit and deny IPv6 addresses.

ipv6 prefix-list v6_addr_filt permit 2001:db8:0:1::/64 ipv6 prefix-list v6_addr_filt permit 2001:db8:0:10::/60 le 64 ipv6 prefix-list v6_addr_filt permit ::/0 ge 62 le 64

The first entry permits prefix 2001:db8:0:1:: with the prefix length exactly 64 bits. The second and third entries permit a range of addresses. The keyword le indicates that the range of prefix lengths to be matched is from the length specified, after the prefix to the length specified after the le keyword. The second entry in the prefix list v6_addr_filt permits prefixes which match 2001:db8:0:10:: and have a length in the range 60 to 64. The ge keyword specifies the minimum length of the prefix in a range of addresses. If it is used with no le keyword, it is assumed that the maximum length for the range of prefixes matched is 128 bits, the maximum number of bits in an IPv6 prefix. When used with the le keyword, the maximum matched length of the range is specified after le. The third entry in prefix list v6_addr_filt permits any prefix with a length between 62 and 64 bits.