Multi-homing using controlled route leakage at a backup service provider
A technique for implementing route aggregation in a computer network containing a multi-homed customer site connected to primary and second networks, which in turn are both connected to a common “backbone” network. According to the technique, the primary network allocates a block of network addresses for the customer site, and the customer site notifies the secondary network of its allocated addresses. The secondary network first determines whether the primary network has already advertised an aggregated route which incorporates the customer site's route. If so, the secondary network “suppresses” (i.e., does not advertise) the customer site's route. The secondary network only “unsuppresses” the customer site's route if it detects that the primary network has lost connectivity to the customer site and/or the backbone network.
1. A method for implementing route aggregation in a computer network containing a multi-homed network connected to primary and secondary networks, the method comprising:
allocating a block of network addresses for the multi-homed network;
notifying the secondary network of the block of network addresses allocated for the multi-homed network;
determining, at a network node of the secondary network, whether the primary network has advertised an aggregated route including the multi-homed network's allocated block of network addresses; and
suppressing, at one or more network nodes of the secondary network, advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has already advertised an aggregated route including the multi-homed network's allocated block of network addresses.
2. The method of claim 1 , wherein the step of determining whether the multi-homed network has lost network connectivity with the primary network further comprises:
sending a message to the secondary network, the message indicating that the multi-homed network has lost network connectivity with the primary network.
3. The method of claim 1 , further comprising:
determining, at the network node of the secondary network, whether the primary network has lost network connectivity with a backbone network; and
unsuppressing, at the one or more network nodes of the secondary network, the advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has lost network connectivity with the backbone network.
4. The method of claim 3 , wherein the step of determining whether the primary network has lost network connectivity with the backbone network further comprises:
sending a message to the secondary network, the message indicating that the aggregated route advertised by the primary network is no longer reachable.
5. The method of claim 1 , wherein the step of notifying the secondary network of the multi-homed network's allocated block of network addresses further comprises:
sending the secondary network (i) at least one address prefix corresponding to the multi-homed network's allocated block of network addresses, (ii) an indication that the multi-homed network is multi-homed and (iii) the aggregated route advertised by the primary network.
6. The method of claim 5 , further comprising:
storing the at least one address prefix corresponding to the multi-homed network's allocated block of network addresses, the indication that the multi-homed network is multi-homed and the aggregated route advertised by the primary network in a dynamic conditional advertisement community (DCAC) attribute; and
sending the DCAC attribute to the secondary network.
7. The method of claim 6 , wherein the DCAC attribute is formatted as an IPv4-address-specific extended community attribute.
8. The method of claim 1 , wherein the step of suppressing advertisements containing the multi-homed network's allocated block of network addresses further comprises:
associating a no_export community attribute with the multi-homed network's allocated block of network addresses.
9. The method of claim 8 , further comprising:
unsuppressing the advertisements containing the multi-homed network's allocated block of network addresses by removing the no_export community attribute.
10. The method of claim 1 , wherein the step of suppressing advertisements containing the multi-homed network's allocated block of network addresses further comprises:
associating a no_advertise community attribute with the multi-homed network's allocated block of network addresses.
11. The method of claim 10 , further comprising:
unsuppressing the advertisements containing the multi-homed network's allocated block of network addresses by removing the no_advertise community attribute.
12. The method of claim 1 , wherein the step of determining whether the primary network has advertised the aggregated route including the multi-homed network's allocated block of network addresses further comprises:
searching a BGP table for the aggregated route.
13. The method of claim 1 , wherein the step of determining whether the primary network has advertised the aggregated route including the multi-homed network's allocated block of network addresses further comprises:
receiving, at the network nodes of the secondary network, a message containing the aggregated route.
14. A computer network that implements route aggregation, the computer network including a multi-homed network connected to primary and secondary networks, the computer network comprising:
means for allocating a block of network addresses for the multi-homed network;
means for notifying the secondary network of the block of network addresses allocated for the multi-homed network;
means for determining, at the secondary network, whether the primary network has advertised an aggregated route including the multi-homed network's allocated block of network addresses; and
means for suppressing, at the secondary network, advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has already advertised an aggregated route including the multi-homed network's allocated block of network addresses.
15. The computer network of claim 14 , further comprising:
means for determining, at the secondary network, whether the primary network has lost network connectivity with a backbone network; and
means for unsuppressing, at the secondary network, the advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has lost network connectivity with the backbone network.
16. A border router deployed in a computer network, the computer network containing a multi-homed network connected to primary and secondary networks, the border router situated in the secondary network, the border router comprising:
a processor;
a network interface adapted to receive a message from the multi-homed network, the message including a block of network addresses allocated for the multi-homed network; and
a memory adapted to store instructions which are executable by the processor for performing the steps of:
determining whether the primary network has advertised an aggregated route including the multi-homed network's allocated block of network addresses; and
suppressing advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has already advertised an aggregated route including the multi-homed network's allocated block of is network addresses.
17. The border router of claim 16 , wherein the memory further comprises instructions for performing the steps of:
determining whether the primary network has lost network connectivity with a backbone network; and
unsuppressing the advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has lost network connectivity with the backbone network.
18. A border router deployed in a computer network, the computer network containing a multi-homed network connected to primary and secondary networks, the border router situated in the multi-homed network, the border router comprising:
a first network interface adapted to receive a block of network addresses from the primary network; and
a second network interface adapted to transmit a message to the secondary network, the message including:
(i) the block of network addresses received at the first network interface,
(ii) an indication that the multi-homed network is multi-homed, and
(iii) an aggregated route advertised by the primary network,
wherein the message indicates to the secondary network that advertisements containing the block of network addresses are to be suppressed as long as the aggregate route is advertised by the primary network.
19. The border router of claim 18 , wherein the message is a Border Gateway Protocol (BGP) message including a dynamic conditional advertisement community (DCAC) attribute configured to store the received block of network addresses, the indication that the multi-homed network is multi-homed and the aggregated route.
20. A computer-readable media storing instructions for execution on a processor for the practice of a method of implementing route aggregation in a computer network containing a multi-homed network connected to primary and secondary networks, the method comprising:
allocating a block of network addresses for the multi-homed network;
notifying the secondary network of the block of network addresses allocated for the multi-homed network;
determining, at the secondary network, whether the primary network has advertised an aggregated route including the multi-homed network's allocated block of network addresses; and
suppressing, at the secondary network, advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has already advertised an aggregated route including the multi-homed network's allocated block of network addresses.
21. The computer-readable media of claim 20 , wherein the method further comprises:
determining, at the secondary network, whether the primary network has lost network connectivity with a backbone network; and
unsuppressing, at the secondary network, the advertisements containing the multi-homed network's allocated block of network addresses in response to determining that the primary network has lost network connectivity with the backbone network.