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Utilisation d’un espace d’adressage IP /31 pour le peering des fournisseurs de services cloud

Puis-je utiliser une adresse de masque de sous-réseau 31 bits pour établir une session de peering BGP avec un fournisseur de services cloud ?

La réponse dépend de deux facteurs :

  • Si votre appareil sur site est capable de prendre en charge une configuration avec un masque de sous-réseau 31 bits.

  • Si le fournisseur de services cloud est capable de prendre en charge une configuration avec un masque de sous-réseau 31 bits.

Prise en charge des appareils sur site

Le système d’exploitation de périphérique réseau le plus courant prend en charge l’utilisation d’un masque de sous-réseau 31 bits, certaines versions plus anciennes affichant un avertissement, par exemple :

```% Warning: use /31 mask on non point-to-point interface cautiously```

Cloud Service Provider support

The majority of Cloud Service Providers support the use of a 31-bit subnet mask, including AWS, Oracle, Alibaba, and IBM. Here are details provided by each CSP:


In December 2000, the Internet Engineering Task Force (IETF) released RFC 3021 for using 31-bit prefixes on IPv4 point-to-point links. The RFC investigates changes to the standards to preserve IP address space and reducing the amount of IP addresses assigned to point-to-point links by allowing the use of 31-bit subnet masks.

At that time, the current practice used a 30-bit subnet mask, which required four addresses per point-to-point link: one network address, two hosts addresses, and one broadcast address.

In a point-to-point link, where there can be only two possible identifying hosts and where any packet which is transmitted by one end of the link is always received by the other, using a mask defining four addresses could be seen as a waste in certain situations. This is why the RFC 3021 was developed. Using a 31-bit subnet mask, there are only two possible addresses: a network address and a broadcast address, but in a point-to-point link, these two must be interpreted as host addresses.

And currently, when a company creates a connection to a Cloud Service Provider, the standard practice uses a 30-bit subnet mask to set up BGP peering with the provider. So, with the IP shortage still a current issue, and with many organizations not having enough IP address space, organizations want to use a 31-bit subnet mask address for establishing a BGP peering session with a Cloud Service Provider.

Dernière mise à jour: 2022-10-13