Capabilities

BGP Capabilities

AFI/SAFI Support in ExaBGP

ExaBGP supports multiple Address Family Identifiers (AFI) and Subsequent Address Family Identifiers (SAFI) for different types of BGP routes. This page documents the capabilities ExaBGP advertises and supports.

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Table of Contents

• Address Family Identifiers (AFI)
• Subsequent Address Family Identifiers (SAFI)
• Supported AFI/SAFI Combinations
• Configuration
• See Also

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Address Family Identifiers (AFI)

AFI identifies the network layer protocol (IP version).

Supported AFIs

AFI	Value	Protocol	RFC	Support
IPv4	1	Internet Protocol version 4	RFC 4760	✅ Full
IPv6	2	Internet Protocol version 6	RFC 4760	✅ Full

ExaBGP supports both IPv4 and IPv6 for all applicable SAFI types.

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Subsequent Address Family Identifiers (SAFI)

SAFI provides additional context about the type of routing information.

Supported SAFIs

SAFI	Value	Name	RFC	Support
Unicast	1	Unicast forwarding	RFC 4760	✅ Full
Multicast	2	Multicast forwarding	RFC 4760	✅ Full
NLRI-MPLS	4	MPLS Labels	RFC 8277	✅ Full
MPLS-VPN	128	MPLS/BGP VPN	RFC 4364	✅ Full
FlowSpec	133	Flow Specification	RFC 5575, RFC 8955	✅ Full
Flow-VPN	134	FlowSpec VPN	RFC 5575	✅ Full
EVPN	70	Ethernet VPN	RFC 7432	✅ Full
BGP-LS	71	BGP Link-State	RFC 7752	✅ Full
RT-Constrain	132	Route Target Constraint	RFC 4684	✅ Full

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Supported AFI/SAFI Combinations

IPv4 Address Families

Family	AFI	SAFI	Configuration	Use Case
IPv4 Unicast	1	1	ipv4 unicast	Standard IPv4 routing
IPv4 Multicast	1	2	ipv4 multicast	IPv4 multicast routing
IPv4 MPLS	1	4	ipv4 nlri-mpls	MPLS label distribution
IPv4 VPN (VPNv4)	1	128	ipv4 mpls-vpn	MPLS L3VPN
IPv4 FlowSpec	1	133	ipv4 flow	DDoS mitigation, traffic filtering
IPv4 Flow-VPN	1	134	ipv4 flow-vpn	FlowSpec in VPN context

IPv6 Address Families

Family	AFI	SAFI	Configuration	Use Case
IPv6 Unicast	2	1	ipv6 unicast	Standard IPv6 routing
IPv6 Multicast	2	2	ipv6 multicast	IPv6 multicast routing
IPv6 MPLS	2	4	ipv6 nlri-mpls	MPLS label distribution
IPv6 VPN (VPNv6)	2	128	ipv6 mpls-vpn	MPLS L3VPN
IPv6 FlowSpec	2	133	ipv6 flow	DDoS mitigation, traffic filtering
IPv6 Flow-VPN	2	134	ipv6 flow-vpn	FlowSpec in VPN context

L2 Address Families

Family	AFI	SAFI	Configuration	Use Case
EVPN	25 (L2VPN)	70	l2vpn evpn	Data center fabrics, VXLAN
VPLS	25 (L2VPN)	65	l2vpn vpls	Virtual Private LAN Service

Special Purpose

Family	AFI	SAFI	Configuration	Use Case
BGP-LS	16388	71	bgp-ls bgp-ls	Topology collection for SDN
RT-Constrain	1	132	ipv4 rtc	Route Target filtering

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Configuration

Enabling Address Families

In ExaBGP configuration:

neighbor 192.0.2.1 {
    router-id 192.0.2.2;
    local-address 192.0.2.2;
    local-as 65001;
    peer-as 65000;

    # Enable specific address families
    family {
        ipv4 unicast;
        ipv4 flow;
        ipv6 unicast;
        ipv6 flow;
        l2vpn evpn;
    }
}

Capability Negotiation

ExaBGP automatically negotiates capabilities during BGP session establishment (OPEN message):

┌─────────────┐         OPEN          ┌─────────────┐
│   ExaBGP    │ ───────────────────> │   Router    │
│             │  Capabilities:        │             │
│             │  - IPv4 unicast       │             │
│             │  - IPv4 flow          │             │
│             │  - IPv6 unicast       │             │
└─────────────┘                       └─────────────┘
       │                                      │
       │ <──────────────────────────────────  │
       │           OPEN (response)            │
       │        Capabilities agreed           │

Viewing Negotiated Capabilities

ExaBGP logs show negotiated capabilities:

neighbor 192.0.2.1 negotiated capability families ( ipv4 unicast ipv4 flow )

API messages (JSON):

{
  "exabgp": "5.0",
  "type": "state",
  "neighbor": {
    "address": {"peer": "192.0.2.1"},
    "state": "established"
  },
  "capabilities": {
    "families": [
      {"afi": "ipv4", "safi": "unicast"},
      {"afi": "ipv4", "safi": "flow"}
    ]
  }
}

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See Also

• Configuration: Neighbor Configuration - Complete neighbor configuration
• Address Families: FlowSpec Overview - FlowSpec (SAFI 133/134)
• Address Families: EVPN Overview - EVPN (SAFI 70)
• Address Families: BGP-LS Overview - BGP Link-State (SAFI 71)
• RFC Information - Detailed RFC implementation status

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References

• RFC 4760 - Multiprotocol Extensions for BGP-4 (AFI/SAFI)
• RFC 5575 - Dissemination of Flow Specification Rules (FlowSpec IPv4)
• RFC 8955 - Dissemination of Flow Specification Rules (FlowSpec IPv6)
• RFC 4364 - BGP/MPLS IP Virtual Private Networks (VPNs)
• RFC 7432 - BGP MPLS-Based Ethernet VPN (EVPN)
• RFC 7752 - North-Bound Distribution of Link-State and Traffic Engineering (BGP-LS)
• RFC 4684 - Constrained Route Distribution for BGP/MPLS IP VPNs
• RFC 8277 - Using BGP to Bind MPLS Labels to Address Prefixes

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👻 Ghost written by Claude (Anthropic AI)