Network route expansion

1. A system for generating route advertisement messages in a computer network, the system comprising a route expansion server connected to routers in the computer network, wherein the route expansion server is configured to:

receive a route expansion message via a computer network, wherein the route expansion message comprises an identifier for a network zone edge router and a first network address prefix;

store the first network address prefix in a route expansion table in association with the network zone edge router;

receive a network route advertisement message from the network zone edge router via the computer network, wherein the network route advertisement message identifies the network zone edge router as a potential next hop for a second network address prefix;

retrieve the first network address prefix from the route expansion table;

generate an expanded network route advertisement message, wherein the expanded network route advertisement message identifies the network zone edge router as a potential next hop for the first network address prefix and additionally identifies the network zone edge router as a potential next hop for the second network address prefix that is identified in the received network route advertisement message; and

transmit the expanded network route advertisement message to another router via the computer network.

2. The system of claim 1 , further comprising a network route management server, configured to:

generate the route expansion message; and

transmit the route expansion message to the route expansion server via the computer network.

3. The system of claim 1 , wherein the first network address prefix identifies a network address block that is a subnet of a network address block that is identified by the second network address prefix.

4. The system of claim 1 , wherein:

the computer network is a multiprotocol label switching (MPLS) network;

the identifier for the network zone edge router is an MPLS label associated with the network zone edge router;

the network route advertisement message comprises the MPLS label associated with the network zone edge router; and

the retrieving the first network address prefix from the route expansion table comprises using the MPLS label associated with the network zone edge router to look up the first network address prefix in the route expansion table.

5. The system of claim 1 , wherein:

the network zone edge router is a first network zone edge router for a first network zone, and the network route advertisement message is a first network route advertisement message;

the route expansion message further comprises an identifier for a second network zone edge router for a second network zone and a third network address prefix; and

the route expansion server is further configured to:

store the third network address prefix in the route expansion table in association with the second network zone edge router,

receive a second network route advertisement message from the second network zone edge router, wherein the second network route advertisement message identifies the second network zone edge router as a potential next hop for the second network address prefix,

retrieve the third network address prefix from the route expansion table,

generate another expanded network route advertisement message, wherein the another expanded network route advertisement message identifies the second network zone edge router as a potential next hop for the second network address prefix and the third network address prefix, and

transmit the another expanded network route advertisement message to the another router via the computer network.

6. The system of claim 1 , wherein:

the route expansion message comprises multiple network address prefixes, including the first network address prefix; and

the route expansion server is further configured to:

store the multiple network address prefixes in the route expansion table in association with the network zone edge router, and

retrieve the multiple network address prefixes from the route expansion table;

wherein the expanded network route advertisement message identifies the network zone edge router as a potential next hop for each of the multiple network address prefixes.

7. A method, comprising:

receiving a route advertisement message at a route expansion server from a router connected to the route expansion server, wherein the route advertisement message comprises a route advertisement for the router, wherein the route advertisement identifies the router as a potential next hop for a first network subdomain;

generating an expanded route advertisement message by the route expansion server based on an identity of the router, wherein the expanded route advertisement message comprises the route advertisement for the router in the received route advertisement message and an additional route advertisement for the router, wherein the additional route advertisement identifies the router as a potential next hop for a second network subdomain; and

transmitting the expanded route advertisement message to another router connected to the route expansion server.

8. The method of claim 7 , wherein the generating the expanded route advertisement message comprises:

using the identity of the router to look up the additional route advertisement in a route expansion table stored on the route expansion server.

9. The method of claim 8 , further comprising:

receiving a subnet expansion set at the route expansion server, wherein the subnet expansion set comprises the additional route advertisement, the identity of the router, and an association between the additional route advertisement and the identity of the router; and

updating the route expansion table to include a mapping between the identity of the router and the additional route advertisement.

10. The method of claim 9 , wherein the subnet expansion set is received from a network management server via a network management plane.

11. The method of claim 7 , wherein:

the router is an edge router for a border gateway protocol autonomous system; and

the additional route advertisement comprises a network layer reachability information update message that identifies the router as a next hop for the second network subdomain.

12. The method of claim 7 , wherein the identity of the router comprises a label received from the router as part of the route advertisement message.

13. The method of claim 7 , wherein:

the route advertisement message received from the router comprises a route advertisement associating the router with a fake domain prefix; and

the generating the expanded route advertisement message comprises replacing the route advertisement associating the router with the fake domain prefix with:

a new route advertisement associating the router with a valid domain prefix, and

the additional route advertisement.

14. The method of claim 13 , wherein the second network subdomain is a subdomain of a network domain associated with the valid domain prefix.

15. A computing device comprising a processor and a computer-readable storage medium storing executable instructions that, when executed by the processor, cause the computing device to perform operations, the operations comprising:

receiving a route advertisement from an edge router for a network zone, wherein the route advertisement comprises an identifier for the edge router and a subnet identifier and identifies the edge router as a potential next hop for a first network subdomain that is associated with the subnet identifier;

determining an additional subnet identifier associated with the edge router using the identifier for the edge router;

generating an expanded route advertisement message, wherein the expanded route advertisement message identifies the edge router as a potential next hop for the first network subdomain that is associated with the subnet identifier in the received route advertisement and additionally identifies the edge router as a potential next hop for a second network subdomain that is associated with the additional subnet identifier; and

transmitting the expanded route advertisement message to a router outside the network zone.

16. The computing device of claim 15 , wherein:

the computing device further comprises a route expansion table comprising route expansion records; and

the determining the additional subnet identifier comprises searching the route expansion table for a route expansion record associated with the identifier for the edge router, and retrieving the additional subnet identifier from the route expansion record associated with the identifier for the edge router.

17. The computing device of claim 16 , wherein:

the route expansion records are associated with keys comprising router identifiers and subnet identifiers; and

the searching the route expansion table comprises using the identifier for the edge router and the subnet identifier as a key to locate the route expansion record.

18. The computing device of claim 15 , wherein:

the first network subdomain comprises an aggregate subnet; and

the second network subdomain comprises a subnet within the aggregate subnet.

19. The computing device of claim 15 , wherein the operations further comprise:

receiving a second route advertisement, wherein the second route advertisement is received from a different edge router for a different network zone, wherein the second route advertisement comprises an identifier for the different edge router and the subnet identifier and identifies the different edge router as a potential next hop for the first network subdomain that is associated with the subnet identifier;

determining a different additional subnet identifier associated with the different edge router using the identifier for the different edge router;

generating another expanded route advertisement message, wherein the another expanded route advertisement message identifies the different edge router as a potential next hop for the first network subdomain that is associated with the subnet identifier and identifies the different edge router as a potential next hop for a third network subdomain that is associated with the different additional subnet identifier; and

transmitting the another expanded route advertisement message to the router outside the network zone, wherein the router outside the network zone is also outside the different network zone.

20. The computing device of claim 15 , wherein the identifier for the edge router received as part of the route advertisement comprises an attribute associated with a border gateway protocol community.