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# Additional Paths
This page explains how to configure BGP Additional Paths features on GoBGP.
GoBGP supports to advertise ADD-PATH capability according to
[RFC7911](https://tools.ietf.org/html/rfc7911) and advertise paths with
the "Advertise N Paths" mode described in
[draft-ietf-idr-add-paths-guidelines](https://tools.ietf.org/html/draft-ietf-idr-add-paths-guidelines).
## Prerequisites
Assumed that you finished [Getting Started](getting-started.md).
## Contents
- [Configuration](#configuration)
- [Verification](#verification)
- [Example Topology and Configuration](#example-topology-and-configuration)
- [Advertise Multiple Paths](#advertise-multiple-paths)
## Configuration
In order to advertise multiple paths to the specific neighbors, you need to
configure `[neighbors.add-paths.config]` section for each neighbor.
In the following example, `send-max = 8` means GoBGP will advertise up to 8
paths per prefix towards this neighbor and `receive = true` enables to
receive multiple paths from this neighbor.
```toml
[[neighbors]]
[neighbors.config]
neighbor-address = "10.0.0.2"
[neighbors.add-paths.config]
send-max = 8
receive = true
```
Also, BGP Additional Paths features are configurable per AFI-SAFI and the per
AFI-SAFI configuration overrides the per neighbor configuration.
The following example enables BGP Additional Paths features for only IPv4
unicast family.
```toml
[[neighbors]]
[neighbors.config]
neighbor-address = "10.0.0.2"
[neighbors.add-paths.config]
receive = false
send-max = 0
[[neighbors.afi-safis]]
[neighbors.afi-safis.config]
afi-safi-name = "ipv4-unicast"
[neighbors.afi-safis.add-paths.config]
receive = true
send-max = 8
```
## Verification
### Example Topology and Configuration
To test BGP Additional Paths features, this page supposes the following
topology.
```text
+----------+ +----------+ +----------+
| r1 | | r2 | | r3 |
| AS 65001 | ADD-PATH enabled | AS 65002 | | AS 65003 |
| 10.0.0.1 |--------------------| 10.0.0.2 |----------| 10.0.0.3 |
+----------+ +----------+ +----------+
|
|
|
+----------+
| r4 |
| AS 65004 |
| 10.0.0.4 |
+----------+
```
Configuration on r1:
```toml
[global.config]
as = 65001
router-id = "10.0.0.1"
[[neighbors]]
[neighbors.config]
neighbor-address = "10.0.0.2"
peer-as = 65002
[neighbors.add-paths.config]
receive = true
send-max = 8
[[neighbors.afi-safis]]
[neighbors.afi-safis.config]
afi-safi-name = "ipv4-unicast"
```
Configuration on r2:
```toml
[global.config]
as = 65002
router-id = "10.0.0.2"
[[neighbors]]
[neighbors.config]
neighbor-address = "10.0.0.1"
peer-as = 65001
[neighbors.add-paths.config]
receive = true
send-max = 8
[[neighbors.afi-safis]]
[neighbors.afi-safis.config]
afi-safi-name = "ipv4-unicast"
[[neighbors]]
[neighbors.config]
neighbor-address = "10.0.0.3"
peer-as = 65003
[[neighbors.afi-safis]]
[neighbors.afi-safis.config]
afi-safi-name = "ipv4-unicast"
[[neighbors]]
[neighbors.config]
neighbor-address = "10.0.0.4"
peer-as = 65004
[[neighbors.afi-safis]]
[neighbors.afi-safis.config]
afi-safi-name = "ipv4-unicast"
```
### Advertise Multiple Paths
Start GoBGP on r1, r2, r3 and r4, and confirm the establishment of each BGP
session.
e.g.:
```bash
r1> gobgpd -f gobgpd.toml
{"level":"info","msg":"gobgpd started","time":"YYYY-MM-DDTHH:mm:ss+09:00"}
{"Topic":"Config","level":"info","msg":"Finished reading the config file","time":""YYYY-MM-DDTHH:mm:ss+09:00"}
{"level":"info","msg":"Peer 10.0.0.2 is added","time":"YYYY-MM-DDTHH:mm:ss+09:00"}
{"Topic":"Peer","level":"info","msg":"Add a peer configuration for:10.0.0.2","time":"YYYY-MM-DDTHH:mm:ss+09:00"}
{"Key":"10.0.0.2","State":"BGP_FSM_OPENCONFIRM","Topic":"Peer","level":"info","msg":"Peer Up","time":"YYYY-MM-DDTHH:mm:ss+09:00"}
```
Advertise a prefix "192.168.1.0/24" on r3 and r4.
```bash
r3> gobgp global rib -a ipv4 add 192.168.1.0/24
```
```bash
r4> gobgp global rib -a ipv4 add 192.168.1.0/24
```
Then confirm 2 paths (from r3 and r4) are advertised to r1 from r2.
In the following output shows the path with AS_PATH 65002 65003 (r3->r2->r1)
and the path with AS_PATH 65002 65004 (r4->r2->r1).
```bash
r1> gobgp global rib -a ipv4
Network Next Hop AS_PATH Age Attrs
*> 192.168.1.0/24 10.0.0.2 65002 65003 HH:mm:ss [{Origin: ?}]
* 192.168.1.0/24 10.0.0.2 65002 65004 HH:mm:ss [{Origin: ?}]
```
|
