Allowed Address Pair: support matching ANY MAC address¶
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Allowed address pairs API allows to match against a subset of IP addresses, or even all of them, by virtue of netmasks being part of ‘ip_address’ field format. For example, using ‘0.0.0.0/0’ means allowing any IP address used with the corresponding MAC address. This proposal suggests extending the API so that a user can allow any MAC address used with the corresponding IP address.
An end user would like to configure their topology so that a port enforces security group rules but allows any MAC addresses. To achieve this, the user:
creates a security group with appropriate rules;
creates a port and assigns it to the security group;
adds allowed address pair for ANY MAC address and some IP address(es).
Right now, the only way to disable MAC address enforcement is to set port_security_enabled attribute to false. But this attribute also disables security group rule enforcement. In this scenario, only anti-spoofing enforcement should be disabled.
The proposal is to extend ‘allowed_address_pairs’ attribute for ports so that its ‘mac_address’ field accepts a special value “ANY” that would disable MAC anti-spoofing mechanism. IP address enforcement may still continue, based on the corresponding ‘ip_address’ field value of the pair.
Having multiple address pairs with “ANY” ‘mac_address’ field value is supported. Having a list of pairs where some but not all ‘mac_address’ field values are “ANY” is supported.
A new Networking API extension will be introduced to indicate support for the new special value. This support is backend specific, which means that ML2 may need to offload decision to enable the extension to underlying drivers.
Database model for allowed address pairs will not need adjustment to accept the new special value because it already accepts all strings.
Client library may need to be adjusted to support the new special value “ANY” for the ‘mac_address’ field in the API validator module.
For agent-based setups, there are two cases to handle where the firewall driver chosen implements anti-spoofing / allowed_address_pair handling itself, and where this task is left to the agent. The firewall driver indicates the former by setting provides_arp_spoofing_protection attribute to True. In this scenario, the driver will have to implement handling of the new “ANY” value set for a MAC-IP pair. A new firewall driver flag (support_any_mac_anti_spoofing) will be added to indicate support for the new feature, defaults to False. If the flag is not set, the agent will filter out ANY address pairs before passing them to the firewall driver. It will also log a warning about the issue. Each driver that handles anti-spoofing itself will need to opt in receiving “ANY” address pairs by setting the support_any_mac_anti_spoofing flag to True.
Instead of using a new special value “ANY”, we could introduce a masking scheme for ‘mac_address’ field. For example, “de:ad:/32” would indicate “any MAC address that starts with de:ad: prefix”. But it’s debatable whether using any mask but /0 is generally useful, since MAC addresses are opaque values with no inherent ordering or grouping (that said, traditionally vendors reuse the same prefixes for their devices).
Instead of reusing the existing allowed address pairs API attribute, we could introduce a new port level attribute that would disable MAC address anti-spoofing without disabling security group rules. Since SG API still allows to match against particular IP addresses, this approach would be functionally identical to this. That said, I think it’s generally better to avoid introducing new attributes to base resources, and it’s better to keep anti-spoofing related functionality under the same attribute.