Route Aggregation

In This Section:

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 - Gaia Portal

To create aggregate routes:

Click the Advanced Routing > Route Aggregation page.
Click Add.
The Add Aggregate Route window opens.
Enter the IPv4 address for the new contributing route.
Enter the Subnet mask.
The IPv4 address and subnet mask correspond to a single routing table entry.
In the Contributing Protocol section, click Add.
The Add Contribution Setting window opens.
Select the Protocol for the new aggregate route.
Optional: Select Contribute All Routes.
Optional: To specify a prefix, fill in the Address and Subnet mask.
Select the Match Type (None, Refines or Exact).
Click Save.

Add Aggregate Route Window

Parameter	Description
IPv4 address	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.
Subnet mask	The mask length of the route that activates the aggregate route, if contributed by the protocol. Range: 0-32. Default: No default.
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. 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.
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. Range: 0-65535. Default: 0.
AS Path Truncate	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.
Contributing Protocol	Contributing protocols whose routes activate the aggregate routes.

Add Contribution Setting window

Parameter	Description
Protocol	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
Contribute All Routes	When selected, lets any routes contributed by the protocol activate the aggregate route. Options: Select / Clear Default: Clear
Address	The IP address of the aggregate route being created. Range: Dotted-quad ([0-255].[0-255].[0-255].[0-255]) Default: No default
Subnet mask	The mask length of the aggregate route being created. Range: 0-32 Default: No default
Match Type	The routes that are filtered for the Address and Subnet mask. These are the ways to compare other routes against it: None - matches any route that equals the specified route or is more specific than the specified route. Exact - matches a route only if it equals the From Address and Subnet mask of the specified route. Refines - matches a route only if it is more specific than the specified route. Options: None, Exact, Refines. Default: None.