Notas ICMP Router Discovery Messages (IRDP)

Um dos protocolos First Hop Redundancy Protocols (FHRP) é o ICMP Router Discovery Messages (IRDP). Os hosts escolhem o gateway dinamicamente com base nas mensagens advertidas pelos routers e na preferência escolhem o gateway.

 

Notas:

  • By default usa advertisements broadcast, em multicast utiliza o IP 224.0.0.1
  • A prefer√™ncia + alta prevalece

Exemplo:

Liga√ß√Ķes:

R4-|                |
—-|switch_L2|-R3R2-|¬†¬†¬†¬†¬†¬†¬†¬†¬†¬†¬†¬†¬†¬†¬† |

R4#
interface FastEthernet0/1
ip address 192.168.20.4 255.255.255.0
 ip irdp
 ip irdp address 192.168.20.254 400
ip irdp preference 40

R2#
interface FastEthernet0/1
ip address 192.168.20.2 255.255.255.0
 ip irdp
 ip irdp address 192.168.20.2 350
ip irdp preference 200

R2(config)#ip gdp irdp
%Cannot start GDP client; system is routing IP

R3(config)#

!O GDP (Router discovery mechanism) deve ser apenas ativado no host, activar o !multicast caso os advertisiments tambem sejam

ip gdp irdp

interface FastEthernet0/0
ip address 192.168.20.1 255.255.255.0
 ip irdp

R3#sh ip route
Gateway         Using  Interval  Priority   Interface
192.168.20.4    IRDP      824       40        FastEthernet0/0
192.168.20.254  IRDP      755     350     FastEthernet0/0
192.168.20.2    IRDP      858       200     FastEthernet0/0

Default gateway is 192.168.20.254

Notas: A decisão do router eleito como gateway, é sempre feita com base na preference atribuída caso seja configurada. Caso contrário na preference do proxy-advertise.

Referências:

RFC 1256 –¬†ICMP Router Discovery Messages

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