RFC 1879 (rfc1879) - Page 3 of 6
Class A Subnet Experiment Results and Recommendations
Alternative Format: Original Text Document
RFC 1879 Class A Subnet Experiment January 1996
Routing
A classic cisco configuration that has the following statements
ip route 39.1.28.0 255.255.255.0
router bgp 64000
redistribute static
will, by default, promote any classful subnet route to a full
classful route (supernet routes will be left alone). This behaviour
can be changed in at least the following two ways:
1:
ip route 39.1.28.0 255.255.255.0
router bgp 64000
no auto-summary
redistribute static
2:
ip route 39.1.28.0 255.255.255.0
router bgp 64000
network 39.1.28.0 mask 255.255.255.0
redistribute static route-map static-bgp
....
access-list 98 deny 39.1.28.0 0.255.255.255
access-list 98 permit any
....
route-map static-bgp
match ip address 98
Users of cisco gear currently need to code the following two
statements:
ip classless
ip subnet-zero
The implication of the first directive is that it eliminates the idea
that if you know how to talk to a subnet of a network, you know how
to talk to ALL of the network.
The second is needed since it is no longer clear where the all-ones
or all-zeros networks are [6].
Other infrastructure gear exhibited similar or worse behaviour.
Equipment that depends on use of a classful routing protocol, such a
RIPv1 are prone to misconfiguration. Tested examples are current
Ascend and Livingston gear, which continue to use RIPv1 as the
default/only routing protocol. RIPv1 use will create an aggregate
Manning Informational