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This feature module describes the IP Summary Address feature for Routing Information Protocol, version 2. It includes information on the benefits of the new feature, supported platforms, related documents, and so forth.
This document includes the following sections:
The IP Summary Address for RIP feature enables Cisco routers running RIPv2 to advertise a summarized local IP address pool on a network access server so that the address pool can be provided to dialup clients. For example, if a local IP address pool of 10.1.1.1 to 10.1.1.254 is configured on the network access server, you could configure the ip summary-address rip 10.1.1.0 255.255.255.0 command on the network access server port that provides addresses to dialup clients to cause the router to advertise 10.1.1.0/24 routes to dialup clients. Because a summary route is advertised, advertisement of the /32 host routes (installed when the dialup client connects) is suppressed so that the router does not advertise these routes to the network access server interface.
When RIP determines that a summary address is required in the RIP database, a summary entry is created in the RIP routing database. As long as there are "child" routes (routes that are created for any combination of the individual IP addresses contained within a summary address), this summary address, the address remains in the routing database. When the last child route is removed, the summary entry also is removed from the database. This method of handling database entries reduces the number of entries in the database because each child route is not listed in an entry, and the aggregate entry itself is removed when there are no longer any valid child routes for it.
RIPv2 route summarization requires that the lowest metric of the "best route" of an aggregated entry, or the lowest metric of all current child routes, be advertised. The best metric for aggregated summarized routes is calculated at route initialization or when there are metric modifications of specific routes at advertisement time, and not at the time the aggregated routes are advertised.
Using the summary IP address feature for RIP means that there is no entry for child routes in the RIP routing table, reducing the size of the table and allowing the router to handle more routes.
Summary IP address functions more efficiently than multiple individually advertised IP routes, because:
Autosummary will override the configured summary-address feature on a given interface except when both of the following are true:
If split horizon is enabled, neither an autosummary address nor the interface summary-address is advertised.
For example, in the following example configuration, the major net is 10.0.0.0. The 10 in the address defines a Class A address space, allowing space for 0.x.x.x unique hosts where x defines unique bit positions in the addresses for these hosts. The summary of the major net defines the prefix as implied by the class (A, B, or C) of the address, without any net mask.
In the following example, the summary address 10.2.0.0 overrides the autosummary address of 10.0.0.0, 10.2.0.0 is advertised out interface E1, and 10.0.0.0 is not advertised.
int E1 ip address 10.1.1.1 255.255.255.0 ip summary-address rip 10.2.0.0 255.255.0.0 no ip split-horizon router rip network 10.0.0.0
Autosummary addressing always summarizes to the classful address boundary, while the ip summary-address is summarized specifically on an interface. If autosummary addressing is enabled, autosummarization is the default behavior for interfaces on the router not associated with dial-in clients (the "backbone"), with OR without the ip summary-address interface subcommand present.
Each route summarization on an interface must have a unique major net, despite unique masks. The current summarization accepted by the parser takes precedence, and must be removed before another summarization sharing same major net can be applied.
Supernet advertisement (advertising any network prefix less than its classful major net) is not allowed, 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:
int 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:
int E1 ... 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)
The IP Summary Address feature for RIPv2 runs on all platforms that support Cisco IOS Release 12.0.
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
No new or modified RFCs are supported by this feature.
See the following "Configuring IP Summary Address for RIPv2" section for configuration task for the IP Summary Address for RIPv2 feature. This task is required.
The ip summary-address rip command causes the router to summarize a given set of routes learned via RIPv2 or redistributed into RIPv2. Host routes are especially applicable for summarization. To configure IP summary addressing, complete the following steps, beginning in router configuration mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router config#rip | Enables RIP routing. | ||
| Router (config-if)#int e1 | Enters interface configuration mode. | ||
| Router (config-if)#ip summary-address rip ip_address ip_network_mask | Specifies the IP address and network mask that identify the routes to be summarized. |
You can verify which routes are summarized for an interface using the show ip protocols command. For example, the following shows potential summarizations and the associated interface summary-address/network mask for Ethernet interface 2:
router#show ip protocols
Routing Protocol is "rip"
Sending updates every 30 seconds, next due in 8 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Outgoing update filter list for all interfaces is
Incoming update filter list for all interfaces is
Redistributing: rip
Default version control: send version 2, receive version 2
Interface Send Recv Triggered RIP Key-chain
Ethernet2 2 2
Ethernet3 2 2
Ethernet4 2 2
Ethernet5 2 2
Automatic network summarization is not in effect
Address Summarization:
12.11.0.0/16 for Ethernet2
You can check summary address entries in the RIP database. These entries will appear in the database only if there are relevant child routes being summarized. When the last child route for a summary address becomes invalid, the summary address is also removed from the routing table. The following example shows a summary address entry for route 12.11.0.0/16, with three child routes active:
router#show ip rip database 11.0.0.0/8 auto-summary 11.11.11.0/24 directly connected, Ethernet2 12.0.0.0/8 auto-summary 12.11.0.0/16 int-summary ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12.11.10.0/24 directly connected, Ethernet3 12.11.11.0/24 directly connected, Ethernet4 12.11.12.0/24 directly connected, Ethernet5
This section provides the following configuration examples:
In the following example the major net is 10.0.0.0. The summary address 10.2.0.0 overrides the autosummary address of 10.0.0.0, so that 10.2.0.0 is advertised out interface e1 and 10.0.0.0 is not advertised.
router rip router int e1 ip address 10.1.1.1 255.255.255.0 (config-if)#ip summary-address rip 10.2.0.0 255.255.0.0 no ip split-horizon router rip network 10.0.0.0 neighbor 2.2.2.2 peer-group mygroup
The following example is illegal, because both addresses to be summarized have the same major net. Each route summarization on an interface must have a unique major net, whether or not the addresses have unique address masks.
int E1 ... ip summary-address rip 10.1.0.0 255.255.0.0 ip summary-address rip 10.2.0.0 255.255.255.0
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command reference publications.
In Cisco IOS Release 12.0(1)T or later, you can search and filter the output for show and more commands. This functionality is useful when you need to sort through large amounts of output, or if you want to exclude output that you do not need to see.
To use this functionality, enter a show or more command followed by the "pipe" character (|), one of the keywords begin, include, or exclude, and an expression that you want to search or filter on:
command | {begin | include | exclude} regular-expression
Following is an example of the show atm vc command in which you want the command output to begin with the first line where the expression "PeakRate" appears:
show atm vc | begin PeakRate
For more information on the search and filter functionality, refer to the Cisco IOS Release 12.0(1)T feature module titled CLI String Search.
To configure a Cisco router running RIPv2 to advertise a summarized local IP address pool on a network access server so that the address pool can be provided to dialup clients and specify the IP address and network mask that identify the routes to be summarized, use the ip summary-address rip router configuration command.
ip summary-address rip ip-address ip_network_mask
ip-address | IP address to be summarized. |
ip_network_mask | IP network mask that drives route summarization for the specified IP address. |
No default behavior or values.
Router configuration.
| Release | Modification |
|---|---|
12.0(6)T | This command was introduced. |
The host name entries are not removed from NVRAM but are cleared in running memory.
In the following example the major net is 10.0.0.0. The summary address 10.2.0.0 overrides the autosummary address of 10.0.0.0, so that 10.2.0.0 is advertised out interface e1 and 10.0.0.0 is not advertised.
router rip router int e1 ip address 10.1.1.1 255.255.255.0 (config-if)#ip summary-address rip 10.2.0.0 255.255.0.0 no ip split-horizon router rip network 10.0.0.0 neighbor 2.2.2.2 peer-group mygroup
| Command | Description |
auto-summary | Restores the default behavior of automatic summarization of subnet routes into network-level routes. |
ip split-horizon | Enables the split horizon mechanism, which blocks information about routes from being advertised by a router out of any interface from which that information originated. |
To display the parameters and current state of the active routing protocol process, use the show ip protocols EXEC command.
show ip protocolsThis command has no arguments or keywords.
No default behavior or values.
EXEC
| Release | Modification |
|---|---|
10.0 | This command was introduced. |
12.0(6)T | Display of information about associated interface summary address and network masks was added. |
The following example shows potential summarizations and the associated interface summary-address/network masks for Ethernet interface 2:
router#show ip prot
Routing Protocol is "rip"
Sending updates every 30 seconds, next due in 8 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Outgoing update filter list for all interfaces is
Incoming update filter list for all interfaces is
Redistributing: rip
Default version control: send version 2, receive version 2
Interface Send Recv Triggered RIP Key-chain
Ethernet2 2 2
Ethernet3 2 2
Ethernet4 2 2
Ethernet5 2 2
Automatic network summarization is not in effect
Address Summarization:
12.11.0.0/16 for Ethernet2
| Command | Description |
ip summary-address rip | Specifies the IP address and network mask for the routes to be summarized. |
show ip rip database | Displays summary address entries in the RIP routing database. |
To display summary address entries in the Routing Information Protocol (RIP) routing database entries if there are relevant routes being summarized based upon a summary address, use the show ip rip database EXEC command.
show ip rip databaseThere are no arguments or keywords for this command.
No default behavior or values.
EXEC
| Release | Modification |
|---|---|
12.0(6) | This command was introduced. |
Summary address entries will appear in the database only if there are relevant child routes being summarized. When the last child route for a summary address becomes invalid, the summary address is also removed from the routing table.
The following example shows a summary address entry for route 12.11.0.0/16, with three child routes active:
router#show ip rip database 11.0.0.0/8 auto-summary 11.11.11.0/24 directly connected, Ethernet2 12.0.0.0/8 auto-summary 12.11.0.0/16 int-summary ^^^^^^^^^^^^^^^^^^^^^^^^^^^ 12.11.10.0/24 directly connected, Ethernet3 12.11.11.0/24 directly connected, Ethernet4 12.11.12.0/24 directly connected, Ethernet5
| Command | Description |
ip summary-address rip | Specifies the IP address and network mask that identify the routes to be summarized. |
show ip protocols | Displays the parameters and current state of the active routing protocol process. |
Posted: Fri Dec 10 18:51:01 PST 1999
Copyright 1989-1999©Cisco Systems Inc.