26.1.3 Advertisement of routing information

<Structure of this section>

(1) Advertised routes

(a) Learning protocol

If filtering of advertised routes has not been specified, learned RIPng routes and directly-connected routes within the RIPng network are advertised. If filtering is specified, the advertising behavior is governed by the filter conditions. The following table describes the learning protocol for route advertising via RIPng.

Table 26-3: Destination learning protocols
Learning protocol		Advertising behavior without route filtering	Order in which advertisement metrics are applied*5
Directly connected route*1	Interface on which RIPng is running	Advertised	Setting for advertised route filtering Default (metric: 1)
Directly connected route*1	Interface other than the above	Not advertised
Summarized route		Not advertised
Static route		Not advertised	Setting for advertised route filtering Setting by default-metric Default (metric: 1)
RIPng^#2		Advertised	Setting for advertised route filtering Metric in the routing table
OSPFv3		Not advertised	Setting for advertised route filtering If inherit-metric is set, the value in the routing table3 Default-metric specification4
BGP4+		Not advertised
Route imported from another VRF or the global network		Not advertised

Note #1: The secondary address is also advertised.
Note #2: Split horizon is applied.
Note #3: The route is not advertised if the metric in the routing table is 16 or higher.
Note #4: The route is not advertised if advertised route filtering is unspecified or if no metric is specified by the inherit-metric or default-metric command.
Note #5: If set, the metric-offset out setting is added to the selected metric. If this results in a metric of 16 or higher, the route is not advertised.

(b) Address type

The following table describes the types of addresses that can be advertised via RIPng.

Table 26-4: Types of routing information
Type of routing information	Definition	Example	Advertised
Default routing information	Routing information about all destination networks	::/0	OK
Network routing information	Global routing information about a specific network destination	2001:db8:1:1::/64 2001:db8:1::/56	OK^#
Host routing information	Global routing information about a specific destination host	2001:db8:1:1::1/128	OK^#

Legend: Y: Can be advertised

#: Only global addresses and local site addresses can be advertised.

(2) Route information advertisement destination

In RIPng, route advertisements are sent to all neighboring routers (including routers on a network to which the interface's secondary address belongs) connected to the interface specified by the ipv6 rip enable configuration command.

(3) Timing of advertisement of routing information

The following table describes the functionality related to the timing of route advertisements distributed via RIPng.

Table 26-5: Route advertisement timing
Functionality	Description
Periodic route advertisement	Neighboring routers are reported periodically about routing information held by the switch.
Triggered update	Any change in the routing information held by the switch is reported immediately without waiting for a periodic advertisement.
Response to a request from a neighboring router	The neighboring router that sent the request packet is notified.
Route poisoning	Neighboring routers are notified for a set duration of any deleted routing information.

(a) Periodic advertisement of routing information

RIPng periodically advertises all routing information held by the local router to neighboring routers. The following figure shows an example of a periodic route advertisement.

Figure 26-1: Advertising periodic routing information

(b) triggered update

Changes in the routing information held by the switch are distributed immediately without waiting for the periodic distribution cycle. The following figure shows a route advertisement distributed as a triggered update.

Figure 26-2: Advertising routing information using triggered update

(c) Response to a request packet

On receipt of a request packet, the Switch sends the requested information to the neighboring router that sent the packet. The following figure shows how routing information is advertised when a request packet is received.

Figure 26-3: Advertising route information when a request packet is received

(d) Root poisoning

When a route changes from reachable to unreachable status (on receipt of a metric-16 route advertisement or on deletion of a route learned from an interface that has since failed), the router advertises the metric-16 (unreachable) route to its neighboring routers for a set period (60 seconds: garbage collection timer). The following figure shows route poisoning.

Figure 26-4: Route poisoning

If a new route to the affected destination is learned while route poisoning is in effect, the Switch advertises the new routing information. This is illustrated in the following figure.

Figure 26-5: Relearning during route poisoning