BGP-LS
BGP-link state (LS) enables BGP to report topology information collected by IGPs to the controller.
BGP-LS is a new method of collecting topology information.
- The controller must have high computing capabilities and support the IGP and its algorithm.
- The controller cannot gain the complete inter-AS topology information and therefore is unable to calculate optimal E2E paths.
- Different IGPs report topology information separately to the controller, which complicates the controller's analysis and processing.
- Reduces computing capability requirements and spares the necessity of IGPs on the controller.
- Facilitates route selection and calculation on the controller by using BGP to summarize process or AS topology information and report the complete information to the controller.
- Requires only one routing protocol (BGP) to report topology information to the controller.
Related Concepts
BGP-LS provides a simple and efficient method of collecting topology information.
BGP-LS routes carry topology information and are classified into three types of routes that carry node, link, and route prefix information, respectively. Theses routes collaborate in carrying topology information.
Format of node routes
For example, a node route is in the format of [NODE][ISIS-LEVEL-1][IDENTIFIER0][LOCAL[as100][bgp-ls-identifier11.1.1.2][ospf-area-id0.0.0.0][igp-router-id0000.0000.0001.00]].
Node routes carry node information.
Table 9-5 describes the fields in node routes.
Item |
Description |
|---|---|
NODE |
Field indicating that the BGP-LS route is a node route. |
ISIS-LEVEL-1 |
Protocol that collects topology information. The protocol is IS-IS in this example. |
IDENTIFIER0 |
Identifier of the protocol that collects topology information. |
LOCAL |
Field indicating information of a local node. |
as |
BGP-LS domain AS number. |
bgp-ls-identifier |
BGP-LS domain ID. |
ospf-area-id |
OSPF area ID. |
igp-router-id |
IGP router ID, generated by the IGP that collects topology information. The router ID is obtained from the NET of an IS-IS process in this example. |
Format of link routes
For example, a link route is in the format of [LINK][ISIS-LEVEL-1][IDENTIFIER0][LOCAL[as255.255][bgp-ls-identifier192.168.102.4][ospf-area-id0.0.0.0][igp-router-id0000.0000.0002.01]][REMOTE[as255.255][bgp-ls-identifier192.168.102.4][ospf-area-id0.0.0.0][igp-router-id0000.0000.0002.00]][LINK[if-address0.0.0.0][peer-address0.0.0.0][if-address::][peer-address::][mt-id0]].
Link routes carry information about links between devices.
Table 9-6 describes the fields in link routes.
Item |
Description |
|---|---|
LINK |
Field indicating that the BGP-LS route is a link route. |
ISIS-LEVEL-1 |
Protocol that collects topology information. The protocol is IS-IS in this example. |
IDENTIFIER0 |
Identifier of the protocol that collects topology information. |
LOCAL |
Field indicating information of a local node. |
as |
BGP-LS domain AS number. |
bgp-ls-identifier |
BGP-LS domain ID. |
ospf-area-id |
OSPF area ID. |
igp-router-id |
IGP router ID, generated by the IGP that collects topology information. The router ID is obtained from the NET of an IS-IS process in this example. |
REMOTE |
Field indicating information of a remote node. |
if-address |
IP address of the local interface. |
peer-address |
IP address of the remote interface. |
mt-id |
ID of the topology. |
Format of prefix routes
For example, a prefix route is in the format of [IPV4-PREFIX][ISIS-LEVEL-1][IDENTIFIER0][LOCAL[as100][bgp-ls-identifier192.168.102.3][ospf-area-id0.0.0.0][igp-router-id0000.0000.0001.00]][PREFIX[mt-id0][ospf-route-type0][prefix192.168.102.0/24]].
Prefix routes carry information about reachable network segments.
Table 9-7 describes the fields in link routes.
Item |
Description |
|---|---|
IPV4-PREFIX |
Field indicating an IPv4 or IPv6 prefix route. The Switch cannot generate IPv6 prefix routes, but it can process the IPv6 prefix routes received from non-Huawei devices. |
ISIS-LEVEL-1 |
Protocol that collects topology information. The protocol is IS-IS in this example. |
IDENTIFIER0 |
Identifier of the protocol that collects topology information. |
LOCAL |
Field indicating information of a local node. |
as |
BGP-LS domain AS number. |
bgp-ls-identifier |
BGP-LS domain ID. |
ospf-area-id |
OSPF area ID. |
igp-router-id |
IGP router ID, generated by the IGP that collects topology information. The router ID is obtained from the NET of an IS-IS process in this example. |
PREFIX |
Field indicating an IGP route. |
mt-id |
ID of the topology. |
ospf-route-type |
OSPF route type:
|
| prefix | Prefix of an IGP route. |
Application Scenarios
Networking in which topology information is collected within an IGP area
In Figure 9-17, SwitchA, SwitchB, SwitchC, and SwitchD use IS-IS to communicate with each other at the network layer. They are all Level-2 devices in the same area (area 10). Only one of the four devices needs to have BGP-LS deployed and establish a BGP-LS peer relationship with the controller so that BGP-LS can collect and report topology information to the controller. To improve reliability, deploying BGP-LS on two or more devices and establishing a BGP-LS peer relationship between each BGP-LS device and the controller are recommended. The BGP-LS devices collect the same topology information, and they back up each other in case one of them fails.
Networking in which topology information is collected between IGP areas
In Figure 9-18, SwitchA, SwitchB, SwitchC, and SwitchD use IS-IS to communicate with each other at the network layer. SwitchA, SwitchB, and SwitchC reside in area 10, whereas SwitchD resides in area 20. SwitchA and SwitchB are Level-1 devices, SwitchC is a Level-1-2 device, and SwitchD is a Level-2 device. Only one of the four devices needs to have BGP-LS deployed and establish a BGP-LS peer relationship with the controller so that BGP-LS can collect and report topology information to the controller. To improve reliability, deploying BGP-LS on two or more devices and establishing a BGP-LS peer relationship between each BGP-LS device and the controller are recommended. The BGP-LS devices collect the same topology information, and they back up each other in case one of them fails.
Networking in which topology information is collected between BGP ASs
In Figure 9-19, SwitchA and SwitchB belong to the same AS, and an IS-IS neighbor relationship is established between them. BGP is disabled on SwitchA. An EBGP peer relationship is established between SwitchB and SwitchC. If BGP-LS is disabled, BGP cannot exchange topology information between AS 100 and AS 200. As a result, the topology information collected in AS 100 is different from that collected in AS 200. To address this problem, enable BGP-LS on at least one device (two or more is recommended for higher reliability) in each AS and establish a BGP-LS peer relationship between each of the devices and the controller.
If two controllers are deployed and are connected to different ASs, for example in Figure 9-20, a BGP-LS peer relationship must be established between the two controllers or between SwitchB and SwitchC so that both controllers can obtain topology information on the whole network.
To reduce the number of connections to the controller, deploy one or more BGP-LS RRs and establish BGP-LS peer relationships between each RR and the devices that require BGP-LS peer relationships with the controller.