ZAPI message to fetch all messages in BGP table at regular interval

[sakthishanmugam02]

hi Team

I am looking for the message that would send the snapshot of all routes learned by the BGP daemon.
Current code what I have done, only fetches all the routes once, and then only the delta (difference) in later calls (even if I restart my program). But I want to fetch all the routes every time I send message to ZAPI. The purpose is to sync the remote route table with current set of learned routes in FRR BGPd.

package main

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

const (

	// Zebra API Server Unix Domain Socket Address - to connect to FRR daemon
	ZEBRA_API_SERVER_ADDRESS = "/var/run/frr/zserv.api"

	// Zebra API version is 6; the packet structure is defined here
	// Ref: http://docs.frrouting.org/projects/dev-guide/en/latest/zebra.html#current-version
	ZEBRA_API_MAX_HEADER_SIZE  = 12
	ZEBRA_API_HEADER_SIZE      = 10
	ZEBRA_API_HEADER_MARKER    = 254
	ZEBRA_API_PROTOCOL_VERSION = 6

	// Zebra Commands
	ZEBRA_HELLO            = 18
	ZEBRA_REDISTRIBUTE_ADD = 11

	// Zebra Routing Info
	// Ref: https://github.com/FRRouting/frr/blob/master/zebra/zebra_rib.c#L100
	ZEBRA_ROUTE_SYSTEM = 0
	ZEBRA_ROUTE_BGP    = 9

	// Zebra Message Payload Defaults
	VRF_DEFAULT = 0
)

func sendHello(conn net.Conn) {

	out := make([]byte, ZEBRA_API_MAX_HEADER_SIZE)
	out[2] = ZEBRA_API_HEADER_MARKER
	out[3] = ZEBRA_API_PROTOCOL_VERSION
	binary.LittleEndian.PutUint32(out[4:], VRF_DEFAULT)
	binary.LittleEndian.PutUint16(out[8:], ZEBRA_HELLO)
	binary.LittleEndian.PutUint16(out[10:], ZEBRA_ROUTE_SYSTEM)
	length := len(out)
	binary.LittleEndian.PutUint16(out[:2], uint16(length))
	response, err := conn.Write(out)
	if err != nil {
		log.Println("Error while sending HELLO to Zebra API Server: ", err)
	}
	log.Println("The response hello is: ", response)
}

func sendRedistribute(conn net.Conn) {

	out := make([]byte, ZEBRA_API_MAX_HEADER_SIZE)
	//binary.LittleEndian.PutUint16(obuf[0:], ZEBRA_HEADER_SIZE)
	out[2] = ZEBRA_API_HEADER_MARKER
	out[3] = ZEBRA_API_PROTOCOL_VERSION
	binary.LittleEndian.PutUint32(out[4:], VRF_DEFAULT)
	binary.LittleEndian.PutUint16(out[8:], ZEBRA_REDISTRIBUTE_ADD)
	binary.LittleEndian.PutUint16(out[10:], ZEBRA_ROUTE_BGP)
	length := len(out)
	binary.LittleEndian.PutUint16(out[:2], uint16(length))
	response, err := conn.Write(out)
	if err != nil {
		log.Println("Error while sending REDISTRIBUTE to Zebra API Server ", err)
	}
	log.Println("The response for redistribute is: ", response)
}

func main() {
	conn, err := net.Dial("unix", ZEBRA_API_SERVER_ADDRESS)
	if err != nil {
		log.Printf("Error while dialing Zebra API Server: %v", err)
	}
	defer conn.Close()

	// Send HELLO to Zebra API Server
	sendHello(conn)

	// Send REDISTRIBUTE to Zebra API Server
	sendRedistribute(conn)

	for {
		// Read from the buffer
		buffer := make([]byte, ZEBRA_API_HEADER_SIZE)
		_, err := conn.Read(buffer)
		if err != nil {
			log.Println("Error while reading from the buffer: ", err)
			return
		}
		log.Println("The message read is: ", buffer)
	}
}

[donaldsharp]

there is no such message. ZEBRA_REDISTRIBUTE_ADD tells zebra to send all the routes for the specified protocol and as changes are given to zebra from the specified protocol they are relayed to the interested party.

I would solve the problem( although I would say this is an actual problem that you would want to solve ) by sending a ZEBRA_REDISTRIBUTE_DELETE then an ZEBRA_REDISTRIBUTE_ADD in quick succession ).

Having zebra send everything and then send as updates happen is the most efficient way of handling large tables.

[sakthishanmugam02]

@donaldsharp I do not see any BGP attributes while parsing the message like AS_PATH, LocalPref etc. How can I get it?

I can only see the following:

{
	"Distance": 20,
	"Family": 2,
	"Flag": "FLAG_ALLOW_RECURSION|FLAG_SELECTED",
	"Message": 23,
	"Metric": 0,
	"Mtu": 0,
	"Nexthop": [{
		"Type": 2,
		"VrfID": 0,
		"Ifindex": 2,
		"Gate": "10.250.0.9",
		"LabelNum": 0,
		"MplsLabels": null
	}],
	"Prefix": "10.100.103.0",
	"PrefixLength": 24,
	"RouteType": 9,
	"api": 30,
	"level": "debug",
	"msg": "ip route message received",
	"time": "2023-03-29T03:57:55-04:00"
}

[mjstapp]

Maybe what you want is more like BMP - did you read about https://docs.frrouting.org/en/latest/bmp.html?
ZAPI is really about what daemons send to zebra, and doesn't include all the internal protocol information specific to any daemon.

[sakthishanmugam02]

@mjstapp Would you be able to provide some references on how to use this BMP?
like how to connect to the local FRR bgp daemon and get the route mirroring starting?

[mjstapp]

I put the reference to the documentation in my message above? I don't really have more info than that...

[sakthishanmugam02]

I followed the docs:

Current configuration:
!
frr version 8.4-dev-MyRPMVersion
frr defaults traditional
hostname sakthi-dev-experiment-bgp-03
log file /var/log/frr/bgpd.log
log syslog
no ip forwarding
no ipv6 forwarding
!
debug zebra events
debug zebra packet recv
debug zebra kernel
debug zebra rib
debug zebra nht
!
router bgp 64520
 no bgp ebgp-requires-policy
 no bgp network import-check
 neighbor 10.250.0.9 remote-as 64521
 neighbor 10.250.0.9 ebgp-multihop 255
 !
 address-family ipv4 unicast
  network 10.250.22.0/24
 exit-address-family
 !
 bmp targets DRS
  bmp stats interval 60000
  bmp mirror

  bmp listener 0.0.0.0 port 6666
 exit
exit
!
ip nht resolve-via-default
!
rpki
exit
!
end

my doubt is how to write a client program to connect to port 6666 to receive the route updates.

[sakthishanmugam02]

I wrote a simple program to connect to BMP server using Golang, looking to parse the message further, Is there any documentation on BMP message formats?

[sakthishanmugam02]

got some hints in RFC specification, thanks!