# IOS-XR BGP Config for ExaBGP Peering

Apply to **both CORE routers** (`CML-R9K-CORE-01` @ 10.100.0.100 and
`CML-R9K-CORE-02` @ 10.100.0.200).

Credentials: `ssh user@<mgmt-ip>` password `cisco`

---

## Route Policy (apply once per router)

```
route-policy EXABGP_IN
  pass
end-policy

route-policy EXABGP_OUT
  drop
end-policy
```

---

## BGP Neighbor Block

```
router bgp 65020
 neighbor 10.40.40.202
  remote-as 65100
  description ExaBGP-Route-Injector
  ebgp-multihop 5
  update-source MgmtEth0/RP0/CPU0/0
  !
  address-family ipv4 unicast
   route-policy EXABGP_IN in
   route-policy EXABGP_OUT out
   next-hop-self
  !
  address-family ipv6 unicast
   route-policy EXABGP_IN in
   route-policy EXABGP_OUT out
   next-hop-self
  !
 !
!
```

### Key config notes

| Knob | Why |
|------|-----|
| `remote-as 65100` | ExaBGP presents as AS 65100 (eBGP to your AS 65020 mesh) |
| `ebgp-multihop 5` | Host (10.40.40.202) and router (10.100.0.x) are different subnets |
| `update-source MgmtEth0/RP0/CPU0/0` | Use management interface for the TCP session |
| `next-hop-self` | Replace ExaBGP's next-hop (10.40.40.202) with the CORE router's loopback when reflecting into iBGP — ensures other routers can resolve the next-hop via ISIS |
| `EXABGP_OUT` drops | Prevent the lab from advertising its own prefixes back to ExaBGP |

---

## Verification Commands

```
show bgp neighbors 10.40.40.202
show bgp neighbors 10.40.40.202 received routes
show bgp summary
show route 1.1.1.0/24
show bgp 1.1.1.0/24
```

After loading the `internet_sample` scenario you should see ~94 new
prefixes in the BGP table and they should propagate to all 9 routers
via the iBGP mesh.

---

## NETCONF push (alternative to CLI)

With NETCONF already enabled, you can push this config programmatically:

```bash
pip install ncclient

python3 - <<'EOF'
from ncclient import manager

ROUTERS = [
    {'host': '10.100.0.100', 'description': 'CML-R9K-CORE-01'},
    {'host': '10.100.0.200', 'description': 'CML-R9K-CORE-02'},
]

POLICY_XML = """
<config>
  <routing-policy xmlns="http://cisco.com/ns/yang/Cisco-IOS-XR-policy-repository-cfg">
    <route-policies>
      <route-policy>
        <route-policy-name>EXABGP_IN</route-policy-name>
        <rpl-route-policy>route-policy EXABGP_IN&#10;  pass&#10;end-policy</rpl-route-policy>
      </route-policy>
      <route-policy>
        <route-policy-name>EXABGP_OUT</route-policy-name>
        <rpl-route-policy>route-policy EXABGP_OUT&#10;  drop&#10;end-policy</rpl-route-policy>
      </route-policy>
    </route-policies>
  </routing-policy>
  <bgp xmlns="http://cisco.com/ns/yang/Cisco-IOS-XR-ipv4-bgp-cfg">
    <instance>
      <instance-name>default</instance-name>
      <instance-as>
        <as>0</as>
        <four-byte-as>
          <as>65020</as>
          <bgp-running/>
          <default-vrf>
            <bgp-entity>
              <neighbors>
                <neighbor>
                  <neighbor-address>10.40.40.202</neighbor-address>
                  <remote-as>
                    <as-xx>0</as-xx>
                    <as-yy>65100</as-yy>
                  </remote-as>
                  <description>ExaBGP-Route-Injector</description>
                  <ebgp-multihop>
                    <max-hop-count>5</max-hop-count>
                  </ebgp-multihop>
                  <update-in-filtering>
                    <enable/>
                  </update-in-filtering>
                  <neighbor-afs>
                    <neighbor-af>
                      <af-name>ipv4-unicast</af-name>
                      <activate/>
                      <route-policy-in>EXABGP_IN</route-policy-in>
                      <route-policy-out>EXABGP_OUT</route-policy-out>
                      <next-hop-self>true</next-hop-self>
                    </neighbor-af>
                    <neighbor-af>
                      <af-name>ipv6-unicast</af-name>
                      <activate/>
                      <route-policy-in>EXABGP_IN</route-policy-in>
                      <route-policy-out>EXABGP_OUT</route-policy-out>
                      <next-hop-self>true</next-hop-self>
                    </neighbor-af>
                  </neighbor-afs>
                </neighbor>
              </neighbors>
            </bgp-entity>
          </default-vrf>
        </four-byte-as>
      </instance-as>
    </instance>
  </bgp>
</config>
"""

for router in ROUTERS:
    print(f"Configuring {router['description']} ({router['host']})...")
    with manager.connect(
        host=router['host'],
        port=830,
        username='user',
        password='cisco',
        hostkey_verify=False,
        device_params={'name': 'iosxr'},
    ) as m:
        m.edit_config(target='candidate', config=POLICY_XML)
        m.commit()
    print(f"  Done.")

print("All routers configured.")
EOF
```