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Route aggregation is a method of generating a more general route, given the presence of a specific route. Use this method to reduce the number of routes advertised for a given protocol. For example, if a router has many stub interface routes subnetted from a class C and is running RIPv2 on another interface, you can use interface routes to create an aggregate route of the class C that can then be redistributed into RIP. This action reduces the number of routes advertised through RIP. Be careful when aggregating if there are "holes" in the route that is aggregated.
The interface that originates the aggregate routes does not use aggregate routes to forward packets. Only the router receiving data can use the Aggregate routes to forward traffic. A router that receives a packet that does not match one of the component routes that generated an aggregate route should respond with an ICMP network unreachable message. This action prevents packets for unknown component routes from following a default route into another network, where they are continually forwarded back to the border router until their TTLs expire.
Create an aggregate route by specifying the network address and mask length and then providing a set of contributing routes. Define a contributing route by specifying a source, such as, a routing protocol, a static route, an interface route, and a route filter, which is either a prefix or the keyword all. An aggregate route can have many contributing routes, but at least one of the routes must be present to generate an aggregate route.
To create aggregate routes
The Add Aggregate Route window opens.
The IPv4 address and subnet mask correspond to a single routing table entry.
The Add Contribution Setting window opens.
Add Aggregate Route Window
Parameter |
Description |
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IPv4 address |
The IPv4 address of a route that activates the aggregate route, if contributed by the protocol.
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Subnet mask |
The mask length of the route that activates the aggregate route, if contributed by the protocol.
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Rank |
The routing system uses rank when there are routes from different protocols to the same destination. For each route, the route from the protocol with the lowest rank is used.
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Weight |
A second tie breaker after the rank. It selects routes going to the same destination. The route with the highest weight is an active route and is installed in the kernel forwarding table and redistributed to other routing protocols.
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AS Path Truncate |
When selected, the AS path is truncated to the longest common AS path.
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Contributing Protocol |
Contributing protocols whose routes activate the aggregate routes. |
Add Contribution Setting window
Parameter |
Description |
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Protocol |
A contributing protocol whose routes activate the aggregate route.
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Contribute All Routes |
When selected, lets any routes contributed by the protocol activate the aggregate route.
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Address |
The IP address of the aggregate route being created.
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Subnet mask |
The mask length of the aggregate route being created.
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Match Type |
The routes that are filtered for the Address and Subnet mask. These are the ways to compare other routes against it:
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Create aggregate routes using these Gaia Clish commands:
set aggregate ip_prefix
contributing protocol <protocol> contributing-route
<all | ip_prefix> <on | off>
<ip_prefix> exact on
<ip_prefix> refines on
off
contributing protocol <protocol> off
rank default
rank <0-255>
weight default
aspath-truncate <on | off>
Parameter |
Description |
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The IP address and mask length of the new aggregate route and the contributing protocol or interface route. To specify a protocol, enter |
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The contributing route is limited to the specified IP address and mask length only. You cannot enable both |
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The contributing route is based on addresses with a greater value than the specified mask length of the specified IP address. You cannot enable both |
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The rank to assign to the aggregate route when routes from different protocols to the same destination are present. For each route, the route from the protocol with the lowest rank is used. Each routing protocol has a different default rank value. Aggregate routes have a default rank of 130. |
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The rank to assign to the aggregate route when routes from different protocols to the same destination are present. For each route, the route from the protocol with the lowest rank is used. Each routing protocol has a different default rank value. Each routing protocol has a different default rank value. Aggregate routes have a default rank of 130. |
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A value that breaks a tie if select routes going to the same destination have the same rank value. The route with the highest weight is the active route. The active route is installed in the kernel forwarding table and redistributed to the other routing protocols.
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A value that breaks a tie if select routes going to the same destination have the same rank value. The route with the highest weight is the active route. The active route is installed in the kernel forwarding table and redistributed to the other routing protocols.
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Specifies that the autonomous system (AS) path be truncated to the longest common AS path. The default behavior is to build an AS path that consists of sets and sequences of all contributing AS paths.
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