Router advertisement caching

1. A controller, comprising:

a processing resource; and

a memory resource storing machine-readable instructions to cause the processing resource to:

cache a router advertisement (RA) from a router of a plurality of routers associated with a virtual local area network (VLAN) of the controller;

select, in response to a client device associating with the controller, the cached RA from the router;

unicast the RA from the router to the client device;

send router solicitations to the plurality of routers of the VLAN of the controller;

unicast, to the client device, a zero lifetime RA in response to the router of the plurality of routers failing to respond to the router solicitation in a predetermined threshold time to cause the client device to disconnect from the router; and

unicast, to the client device associated with the router of the plurality of routers, a different RA associated with a different router of the plurality of routers to cause the client device to connect to the different router.

2. The controller of claim 1 , wherein the RA is unicast to the client device to cause the client device to connect to the router.

3. The controller of claim 1 , wherein the RA from the router is selected in response to receiving a router solicitation from the client device.

4. The controller of claim 1 , wherein the controller is included in a switch.

5. The controller of claim 1 , wherein the controller is included in an access point (AP).

6. A non-transitory machine-readable medium storing instructions executable by a processing resource to:

cache, by a controller, a router advertisement (RA) received from a first router of a plurality of routers and an RA received from a second router of the plurality of routers;

select, in response to a client device associating with the controller, the RA received from the first router;

unicast the selected RA from the first router to the client device to cause the client device to connect to the first router;

send, by the controller, router solicitations to the plurality of routers of the VLAN of the controller;

unicast, to the client device associated with the router of the plurality of routers, a zero lifetime RA in response to the router of the plurality of routers failing to respond to the router solicitation in a predetermined threshold time to cause the client device to disconnect from the router; and

unicast, to the client device associated with the router of the plurality of routers, a different RA associated with a different router of the plurality of routers to cause the client device to connect to the different router.

7. The medium of claim 6 , comprising instructions to:

select, in response to a different client device associating with the controller, the RA received from the second router; and

unicast the RA from the second router to the different client device to cause the different client device to connect to the second router.

8. The medium of claim 6 , wherein an RA received from the first or the second router is selected by round-robin selection.

9. The medium of claim 6 , wherein an RA received from the first or the second router is selected based on router information, including at least one of:

a plurality of client devices associated with each router of the plurality of routers;

response times of each router of the plurality of routers;

a priority of each router of the plurality of routers;

bandwidth of each router of the plurality of routers; and

data throughput of each router of the plurality of routers.

10. The medium of claim 6 , wherein an RA received from the first or the second router is selected based on client device information, including at least one of:

client device type;

a role associated with the client device;

time of day;

client association history; and

client activity history.

11. The medium of claim 6 , wherein:

the first router and the second router are associated with a virtual local area network (VLAN); and

the VLAN operates on an Internet Protocol version 6 (IPv6) protocol.

12. A method, comprising:

determining, by a controller, a plurality of routers associated with a virtual local area network (VLAN) of the controller;

caching, by the controller, a plurality of router advertisements (RAs) received from the plurality of routers of the VLAN;

selecting, by the controller in response to a client device associating with the controller, an RA associated with a router of the plurality of routers;

unicasting the selected RA of the router to the client device to cause the client device to connect to the router;

sending, by the controller, router solicitations to the plurality of routers of the VLAN of the controller;

unicasting, to the client device associated with the router of the plurality of routers, a zero lifetime RA in response to the router of the plurality of routers failing to respond to the router solicitation in a predetermined threshold time to cause the client device to disconnect from the router; and

unicasting, to the client device associated with the router of the plurality of routers, a different RA associated with a different router of the plurality of routers to cause the client device to connect to the different router.

13. The method of claim 12 , wherein causing the client device to connect to the router includes causing the client device to:

generate an Internet Protocol (IP) address based on prefix information included in the RA associated with the router; and

populate a gateway included in a routing table of the client device.

14. The controller of claim 1 , further comprising the memory resource storing the machine-readable instructions to cause the processing resource to cache an RA received from the different router of the plurality of routers.

15. The controller of claim 14 , wherein an RA received from the router or different router is selected based on client device information, including at least one of:

client device type;

a role associated with the client device; and

time of day.

16. The controller of claim 14 , further comprising the memory resource storing the machine-readable instructions to:

select, in response to a different client device associating with the controller, the RA received from the different router; and

unicast the RA from the different router to the different client device to cause the different client device to connect to the different router.

17. The method of claim 12 , wherein the plurality of router advertisements (RAs) cached by the controller includes an RA received from the different router of the plurality of routers.

18. The method of claim 17 , wherein an RA received from the router or different router is selected based on client device information, including at least one of:

client device type; and

a role associated with the client device.

19. The method of claim 17 , further comprising:

selecting, in response to a different client device associating with the controller, the RA received from the different router; and

unicasting the RA from the different router to the different client device to cause the different client device to connect to the different router.

20. The method of claim 12 , further comprising sending the router solicitations to the plurality of routers of the VLAN of the controller at a predetermined frequency.