How to fetch BGP routes from the FRR - ZAPI example

[sakthishanmugam02]

hi Team

I am trying to read the routes from BGP route table - basically the routes are there in show ip bgp command output with all next hop for the destination; I tried to connect ZAPI client for this - I could successfully connect my system client with HELLO message.

Client: system
------------------------
FD: 30
Connect Time: 00:00:02
Not registered for Nexthop Updates
Client will Not be notified about it's routes status
Last Msg Rx Time: 00:00:02
Last Msg Tx Time: never
Last Rcvd Cmd: ZEBRA_HELLO

Type        Add         Update      Del
==================================================
IPv4        0           0           0
IPv6        0           0           0
Redist:v4   0           0           0
Redist:v6   0           0           0
VRF         0           0           0
Connected   0           0           0
Interface   0           0           0
Intf Addr   0           0           0
BFD peer    0           0           0
NHT v4      0           0           0
NHT v6      0           0           0
VxLAN SG    0           0           0
VNI         0           0           0
L3-VNI      0           0           0
MAC-IP      0           0           0
ES          0           0           0
ES-EVI      0           0           0
Errors: 0

But after that, what I should do to get the BGP table information - what message I suppose to send?

When I tried to send redistribute ZEBRA_REDISTRIBUTE_ADD - the client that was connecting before - not connecting. => not showing up in show zebra client

What I should do to get all the routes learned from BGP?

Note: FPM only giving me the best routes selected for the BGP if I have more than one routes to the same destination prefix. But I want all the routes.

cc: @donaldsharp - Could you help?

[sakthishanmugam02]

This is the small program what I written :
When I just keep the HELLO message, zebra lists system client - when I fired Redistribute message - the client disconnects.

Note:

I enabled this logs also but it is giving me any logs.

debug zebra events
debug zebra packet recv

package main

import (
	"encoding/binary"
	"fmt"
	"net"
)

const (
	// Zebra API - ZAPI unix socket address
	ZAPI_SERV_ADDRESS = "/var/run/frr/zserv.api"
)

const (
	ZAPI_HEADER_SIZE   uint16 = 10
	ZAPI_HEADER_MARKER uint8  = 254
	ZAPI_VERSION       uint8  = 6
	DEFAULT_VRF        uint32 = 0

	ZAPI_HELLO            uint16 = 18
	ZAPI_REDISTRIBUTE_ADD uint16 = 11

	routeSystem  uint8 = 0
	routeKernel  uint8 = 1
	routeConnect uint8 = 2
	RouteStatic  uint8 = 3
	RouteBGP     uint8 = 9
)

func main() {
	conn, err := net.Dial("unix", ZAPI_SERV_ADDRESS)
	if err != nil {
		fmt.Println("Error while dialing to ZAPI_SERV_ADDRESS: ", err)
	}
	defer conn.Close()

	// Prepare HelloMessage
	helloHeader := populateHeader(ZAPI_HELLO)

	var helloBody []byte
	helloBody = make([]byte, 9)
	helloBody[0] = uint8(RouteBGP)
	binary.BigEndian.PutUint16(helloBody[1:3], 0)
	binary.BigEndian.PutUint32(helloBody[3:7], 0)
	helloBody[7] = uint8(0)
	helloBody[8] = uint8(0)

	helloMessage := append(helloHeader, helloBody...)
	fmt.Println(helloMessage)
	_, err = conn.Write(helloMessage)
	if err != nil {
		fmt.Println("Error while writing HELLO message to Zebra")
		return
	}

	// Prepare Redistribute Message
	redistributeHeader := populateHeader(ZAPI_REDISTRIBUTE_ADD)

	redistributeBody := make([]byte, 4)
	redistributeBody[0] = uint8(1) // IPv4 
	redistributeBody[1] = uint8(RouteBGP)
	binary.BigEndian.PutUint16(redistributeBody[2:4], 0)

	redistributeMessage := append(redistributeHeader, redistributeBody...)
	fmt.Println(redistributeMessage)
	_, err = conn.Write(redistributeMessage)
	if err != nil {
		fmt.Println("Error while writing REDISTRIBUTE message to Zebra")
		return
	}

	for {
	}
}

func populateHeader(messageType uint16) []byte {
	header := make([]byte, ZAPI_HEADER_SIZE)
	binary.BigEndian.PutUint16(header[0:2], ZAPI_HEADER_SIZE)
	header[2] = ZAPI_HEADER_MARKER
	header[3] = ZAPI_VERSION
	binary.BigEndian.PutUint32(header[4:8], uint32(DEFAULT_VRF))
	binary.BigEndian.PutUint16(header[8:10], messageType)
	return header
}

This is the message stream sent for HELLO and REDISTRIBUTE

[0 10 254 6 0 0 0 0 0 18 9 0 40 0 0 0 0 0 0] => HELLO
[0 10 254 6 0 0 0 0 0 11 1 9 0 40] => RESDISTRIBUTE

@donaldsharp please share your opinion

[sakthishanmugam02]

Figured out the issue: - I missed to add the data payload as part of the length parameter.
Here is the updated code for other's references. Thanks.

package main

import (
	"encoding/binary"
	"fmt"
	"io"
	"net"
)

const (
	// Zebra API - ZAPI unix socket address
	ZAPI_SERV_ADDRESS = "/var/run/frr/zserv.api"
)

const (
	ZAPI_HEADER_SIZE   uint16 = 10
	ZAPI_HEADER_MARKER uint8  = 254
	ZAPI_VERSION       uint8  = 6
	DEFAULT_VRF        uint32 = 0

	ZAPI_HELLO            uint16 = 18
	ZAPI_REDISTRIBUTE_ADD uint16 = 11

	routeSystem  uint8 = 0
	routeKernel  uint8 = 1
	routeConnect uint8 = 2
	RouteStatic  uint8 = 3
	RouteBGP     uint8 = 9
)

func main() {
	conn, err := net.Dial("unix", ZAPI_SERV_ADDRESS)
	if err != nil {
		fmt.Println("Error while dialing to ZAPI_SERV_ADDRESS: ", err)
	}
	defer conn.Close()

	// Prepare HelloMessage
	helloHeader := populateHeader(ZAPI_HELLO, 19)

	var helloBody []byte
	helloBody = make([]byte, 9)
	helloBody[0] = uint8(RouteBGP)
	binary.BigEndian.PutUint16(helloBody[1:3], 0)
	binary.BigEndian.PutUint32(helloBody[3:7], 0)
	helloBody[7] = uint8(0)
	helloBody[8] = uint8(0)

	helloMessage := append(helloHeader, helloBody...)
	fmt.Println(helloMessage)
	_, err = conn.Write(helloMessage)
	if err != nil {
		fmt.Println("Error while writing HELLO message to Zebra")
		return
	}

	// Prepare Redistribute Message
	redistributeHeader := populateHeader(ZAPI_REDISTRIBUTE_ADD, 14)

	redistributeBody := make([]byte, 4)
	redistributeBody[0] = uint8(1) 
	redistributeBody[1] = uint8(RouteBGP)
	binary.BigEndian.PutUint16(redistributeBody[2:4], 0)

	redistributeMessage := append(redistributeHeader, redistributeBody...)
	fmt.Println(redistributeMessage)
	_, err = conn.Write(redistributeMessage)
	if err != nil {
		fmt.Println("Error while writing REDISTRIBUTE message to Zebra")
		return
	}

	for {
		fmt.Println("Listening..")
		in_buf := make([]byte, ZAPI_HEADER_SIZE)
		num, err := io.ReadFull(conn, in_buf)
		fmt.Println("Message read: ", num)
		if err != nil {
			fmt.Println("Error while reading from connection: ", err)
			return
		}
	}

}

func populateHeader(messageType uint16, len uint16) []byte {
	header := make([]byte, ZAPI_HEADER_SIZE)
	binary.BigEndian.PutUint16(header[0:2], len)
	header[2] = ZAPI_HEADER_MARKER
	header[3] = ZAPI_VERSION
	binary.BigEndian.PutUint32(header[4:8], uint32(DEFAULT_VRF))
	binary.BigEndian.PutUint16(header[8:10], messageType)
	return header
}