RIPv2 with the no auto-summary
option will advertise the specific routes, not the aggregated prefix, unless you you use the ip summary-address rip
interface command.
The network statements in RIP are not specifically telling RIP what prefix(es) to advertise, they tell RIP which interfaces should participate in RIP, and RIP will get the specific prefix(es) from the interface(s) which fall into the network statement. This is true for most routing protocols on Cisco routers, and it is a source of confusion for many people. For instance:
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
interface FastEthernet0/1
ip address 10.2.2.1 255.255.255.0
interface FastEthernet1/0
ip address 172.16.1.1 255.255.255.0
router rip
version 2
no auto-summary
network 10.0.0.0
The above configuration will run RIP on F0/0
and F0/1
, but not F1/0
. RIP will advertise two routes: 10.1.1.0/24
and 10.2.2.0/24
.
There are Cisco documents, such as Configuring Routing Information Protocol which explain RIP route summarization:
Restrictions to RIP Route Summarization
Supernet advertisement (advertising any network prefix less than its
classful major network) is not allowed in RIP route summarization,
other than advertising a supernet learned in the routing tables.
Supernets learned on any interface that is subject to configuration
are still learned. For example, the following summarization is
invalid:
interface E1
.
.
.
ip summary-address rip 10.0.0.0 252.0.0.0 (invalid supernet summarization)
Each route summarization on an interface must have a unique major net,
even if the subnet mask is unique. For example, the following is not
permitted:
interface Ethernet1
.
.
.
ip summary-address rip 10.1.0.0 255.255.0.0
ip summary-address rip 10.2.0.0 255.255.0.0 (or different mask)