Peering eBGP sobre vPC en Nexus

Introducción

Este documento describe cómo configurar y verificar el peering e-Border Gateway Protocol (eBGP) entre el par vPC Nеxus y otro dispositivo. Para mayor claridad, la configuración del dispositivo externo se muestra como Cisco CLI NX-OS.

Prerequisites

Requirements

Cisco recomienda que tenga conocimiento sobre estos temas:

• Conceptos básicos de configuración y funcionamiento de vPC. Para consultar: https://www.cisco.com/c/dam/en/us/td/docs/switches/datacenter/sw/design/vpc_design/vpc_best_practices_design_guide.pdf
• Configuración y funcionamiento de BGP

Componentes Utilizados

La información que contiene este documento se basa en las siguientes versiones de software y hardware.

leaf1#	C93108TC-FX	NXOS 9.3(3)
leaf2#	C93108TC-FX	NXOS 9.3(3)
Dispositivo externo	N9K-C9396PX	NXOS: versión 9.2(3)

La información que contiene este documento se creó a partir de los dispositivos en un ambiente de laboratorio específico. Todos los dispositivos que se utilizan en este documento se pusieron en funcionamiento con una configuración verificada (predeterminada). Si tiene una red en vivo, asegúrese de entender el posible impacto de cualquier comando.

Antecedentes

Protocolos de routing (OSPF, ISIS, RIP, EIGRP, BGP) que emparejan un par vPC y un dispositivo externo. Esto es compatible con: https://www.cisco.com/c/en/us/support/docs/ip/ip-routing/118997-technote-nexus-00.html. En este artículo se describen notas adicionales y ejemplos de configuración para eBGP como protocolo de routing.

Se plantean varios problemas al intentar habilitar el peering del protocolo de ruteo sobre un vPC, que no existen cuando se utiliza 

canal de puerto estándar:

1. No es determinístico qué miembro del canal de puerto utilizará el dispositivo externo para reenviar el tráfico para cada dirección MAC. Es posible que el dispositivo externo envíe paquetes BGP para Leaf-1 a través del link a Leaf-1. Cuando Leaf-1 lo recibe, lo dirigirá a la CPU y lo descartará (no su propia dirección IP), por lo que BGP (unidifusión) u otro protocolo (multidifusión) estará inestable constantemente. Aquí ayuda el comando peer-gateway.
2. Incluso con el comando peer-gateway, el TTL disminuirá en dicho paquete. El nuevo comando en NX-OS: router de par de capa 3 lo deshabilita.
3. Se necesita iBGP entre los dos miembros vPC para obedecer la regla BGP para iBGP entre todos los vecinos. Estamos ejecutando dentro de vrf en el lado vPC, por lo tanto, solo esos dos miembros necesitan ejecutar iBGP. Esto también es necesario en caso de fallo de enlace para el resto de la red NX-OS (VXlan u otra) y proporcionar redundancia.
   
   

Configurar

Diagrama de la red

Se necesitan dos comandos importantes para habilitar este peering:

• Peer-gateway: la funcionalidad de par-gateway de vPC permite que un switch vPC actúe como gateway activo para los paquetes que se dirigen a la dirección MAC del router del par vPC

• router de peer de capa 3 - sin cambios para el TTL de los paquetes destinados al par, el dispositivo externo ve el dominio vPC como una sola entidad física desde la perspectiva de peering del protocolo de ruta de capa también.

Configuraciones

Leaf 1:
! Form the vPC domain:
vpc domain 1
  peer-switch
  role priority 10 peer-keepalive destination 192.0.2.2 source 192.0.2.1 peer-gateway layer3 peer-router ipv6 nd synchronize ip arp synchronize
!
!vPC peer-link interface members
interface Ethernet1/53 - 54
  description vPC-Peerlink member
  switchport
  switchport mode trunk
  channel-group 11 mode active
  no shutdown
!
! vPC peer-link port-channel
interface port-channel11
  description vPC-peerlink
  switchport
  switchport mode trunk
  spanning-tree port type network
  no shutdown
  vpc peer-link
!
! vPC port-channel member to External Device
interface Ethernet1/52
  description ExternalDevice Eth2/13
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 203,205
  mtu 9216
  channel-group 12 mode active
  no shutdown
!
! vPC port-channel to External Device
interface port-channel12
  description vPC port-channel to External Device
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 203,205
  mtu 9216
  vpc 12
!
! Layer 3 interface to the Eternal device:
interface Vlan205
  no shutdown
  vrf member Customer
! BFD for eBGP
  bfd interval 500 min_rx 500 multiplier 3
! Disable bfd echo, as it is not supported over vPC
  no bfd echo
  no ip redirects
! We use/29 as we need 3 ip address, one per each member of the ! vPC domain and 3rd for the External Device
  ip address 198.51.100.1/29 tag 800204
! Disable redirects - this is needed to enable BFD
  no ipv6 redirects
!
router bgp 65535
router bgp 65535
  router-id 203.0.113.1
  log-neighbor-changes
  address-family ipv4 unicast
   Customer router-id 198.51.100.1 address-family ipv4 unicast neighbor 198.51.100.2 description Leaf-2 remote-as 65535 address-family ipv4 unicast soft-reconfiguration inbound always neighbor 198.51.100.3 description to External Device bfd remote-as 65000 update-source Vlan205 address-family ipv4 unicast soft-reconfiguration inbound always ! Leaf 2:
! Form the vPC domain:
vpc domain 1
  peer-switch
  role priority 10
  peer-keepalive destination 192.0.2.1 source 192.0.2.2
  peer-gateway
  layer3 peer-router
  ipv6 nd synchronize
  ip arp synchronize
!
!vPC peer-link interface members
interface Ethernet1/53 - 54
  description vPC-Peerlink member
  switchport
  switchport mode trunk
  channel-group 11 mode active
  no shutdown
!
! vPC peer-link port-channel
interface port-channel11
  description vPC-peerlink
  switchport
  switchport mode trunk
  spanning-tree port type network
  no shutdown
  vpc peer-link
!
! vPC port-channel member to External Device
interface Ethernet1/52
  description ExternalDevice Eth2/13
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 203,205
  mtu 9216
  channel-group 12 mode active
  no shutdown
!
! vPC port-channel to External Device
interface port-channel12
  description vPC port-channel to External Device
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 203,205
  mtu 9216
  vpc 12
!
! Layer 3 interface to the Eternal device:
interface Vlan205
  no shutdown
  vrf member Customer
! BFD for eBGP
  bfd interval 500 min_rx 500 multiplier 3
! Disable bfd echo, as it is not supported over vPC
  no bfd echo
  no ip redirects
! We use/29 as we need 3 ip address, one per each member of the ! vPC domain and 3rd for the External Device
  ip address 198.51.100.2/29 tag 800204
! Disable redirects - this is needed to enable BFD
  no ipv6 redirects
!
router bgp 65535
router bgp 65535
  router-id 203.0.113.2
  log-neighbor-changes
  address-family ipv4 unicast
 vrf Customer
    router-id 198.51.100.2
    address-family ipv4 unicast
    neighbor 198.51.100.1
      description Leaf-2
      remote-as 65535
      address-family ipv4 unicast
        soft-reconfiguration inbound always
    neighbor 198.51.100.3
      description to External Device
      bfd
      remote-as 65000
      update-source Vlan205
      address-family ipv4 unicast
        soft-reconfiguration inbound always
!
External Device (NX-OS style CLI):
interface Ethernet2/13 - 14
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 203,205
  mtu 9216
  channel-group 12 mode active
  no shutdown
!
interface port-channel12
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 203,205
  mtu 9216
  no shutdown
!
interface Vlan205
  no shutdown
  mtu 9216
! See notes in Leaf-1 and Leaf 2 for BFD
  bfd interval 500 min_rx 500 multiplier 3
  no bfd echo
  no ip redirects
  ip address 198.51.100.3/29
  no ipv6 redirects
!
router bgp 65000
  log-neighbor-changes
  address-family ipv4 unicast
   neighbor 198.51.100.1 remote-as 65535
      description to Leaf-1
      update-source Vlan205
      bfd
   neighbor 198.51.100.2 remote-as 65535
      description to Leaf-2
      update-source Vlan205
      bfd
end
!

Verificación

A continuación se muestra el resultado de show bgp ipv4 unicast neighbors. Verifica que:

1. La vecindad BGP está establecida y es estable
2. BFD se habilita entre vecinos externos

Leaf 1/2: show bgp ipv4 unicast neighbors vrf Customer BGP neighbor is 203.0.113.2, remote AS 65535, ibgp link, Peer index 4 BGP version 4, remote router ID 203.0.113.2 Neighbor previous state = OpenConfirm BGP state = Established, up for 6d22h Neighbor vrf: Customer Peer is directly attached, interface Vlan205 Last read 00:00:14, hold time = 180, keepalive interval is 60 seconds Last written 00:00:03, keepalive timer expiry due 00:00:56 Received 10012 messages, 0 notifications, 0 bytes in queue ... BGP neighbor is 203.0.113.2.3, remote AS 65000, ebgp link, Peer index 3 BGP version 4, remote router ID 203.0.113.2 Neighbor previous state = OpenConfirm BGP state = Established, up for 1d00h Neighbor vrf: Customer Using Vlan205 as update source for this peer Peer is directly attached, interface Vlan205 BFD live-detection is configured and enabled, state is Up Last read 00:00:22, hold time = 180, keepalive interval is 60 seconds Last written 00:00:56, keepalive timer expiry due 00:00:03 ! External Device: show bgp ipv4 unicast neighbors BGP neighbor is 203.0.113.1, remote AS 65535, ebgp link, Peer index 3 Inherits peer configuration from peer-template Cust_BGP_Peer BGP version 4, remote router ID 203.0.113.1 BGP state = Established, up for 1d00h Peer is directly attached, interface Vlan205 Enable logging neighbor events BFD live-detection is configured and enabled, state is Up Last read 0.660288, hold time = 180, keepalive interval is 60 seconds Last written 00:00:26, keepalive timer expiry due 00:00:33 Received 10122 messages, 1 notifications, 0 bytes in queue Sent 10086 messages, 1 notifications, 0(0) bytes in queue Connections established 14, dropped 13 Last reset by us 1d00h, due to bfd session down Last reset by peer 6d22h, due to other configuration change ....

Troubleshoot

Los siguientes comandos ayudarán a verificar la operación:

show vpc show vpc consistency-parameters global show vpc consistency-parameters interface show bgp ipv4 unicast neighbors show bgp ipv4 unicast summary