Route Aggregation
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.
Configuring Route Aggregation - WebUI
To create aggregate routes
- Go to the page of the WebUI.
- Click .
The window opens.
- Enter the for the new contributing route.
- Enter the .
The IPv4 address and subnet mask correspond to a single routing table entry.
- In the section, click .
The window opens.
- Select the for the new aggregate route.
- Optional: Select .
- Optional: To specify a prefix, fill in the and .
- Select the (None, Refines or Exact).
- Click .
Add Aggregate Route Window
Parameter
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Description
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The IPv4 address of a route that activates the aggregate route, if contributed by the protocol.
- Range: Dotted-quad ([0-255].[0-255].[0-255].[0-255])
- Default: No default.
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The mask length of the route that activates the aggregate route, if contributed by the protocol.
- Range: 0-32.
- Default: No default.
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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.
- Range: 0-255.
- Default: Each routing protocol has a default rank value. Aggregate routes have a default rank of 130. The default value for OSPF is 10, and the default value for RIP is 100.
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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.
- Range: 0-65535.
- Default: 0.
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When selected, the AS path is truncated to the longest common AS path.
- Options: Select / Clear
- Default: Clear. Build an AS path consisting of SETs and SEQUENCEs of all contributing AS paths
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Contributing protocols whose routes activate the aggregate routes.
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Add Contribution Setting window
Parameter
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Description
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A contributing protocol whose routes activate the aggregate route.
- Range: All routing protocols, as well as interface routes, aggregate routes, and static routes. Select one of the following: All / Direct / Static / Aggregate / OSPF2 / OSPF2ASE/ RIP /BGP.
- Default: No default
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When selected, lets any routes contributed by the protocol activate the aggregate route.
- Options: Select / Clear
- Default: Clear
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The IP address of the aggregate route being created.
- Range: Dotted-quad ([0-255].[0-255].[0-255].[0-255])
- Default: No default
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The mask length of the aggregate route being created.
- Range: 0-32
- Default: No default
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The routes that are filtered for the and . These are the ways to compare other routes against it:
- matches any route that equals the specified route or is more specific than the specified route.
- matches a route only if it equals the and of the specified route.
- matches a route only if it is more specific than the specified route.
- Options: None, Exact, Refines.
- Default: None.
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Configuring Route Aggregation - CLI (aggregate)
Create aggregate routes using these 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>
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Parameter
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Description
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contributing protocol <protocol> contributing‑route <all | ip_prefix <on | off>
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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 direct, static, ospf2, ospf2ase, bgp, rip, igrp, rip, or aggregate. To specify a contributing route, enter all to contribute all the routes for a specific protocol or enter the IP address and mask length to contribute a specific route.
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<ip_prefix> exact on
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The contributing route is limited to the specified IP address and mask length only.
You cannot enable both exact on and refines on at the same time. If you enable refines on when exact on is enabled, exact on is automatically disabled.
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<ip_prefix> refines on
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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 exact on and refines on at the same time. If you enable refines on when exact on is enabled, exact on is automatically disabled.
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rank default
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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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rank <0‑255>
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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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weight default
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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.
- Range: 0-65535.
- Default: 0
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weight <0‑65535>
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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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aspath‑truncate <on | off>
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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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