In order for the static host to be operational, forwarding traffic bidirectional, the MAC address of the host must be learned or configured. Learning the MAC of the static host is different for IPv4 or IPv6.
If an IPv4 static host MAC is not specified:
The system learns respective MAC address dynamically from ARP packets (arp-request or gratuitous-arp) generated by the host with the specified IP address.
On a VPLS service, this can occur if arp-reply-agent function is enabled on a specific SAP. On Layer 3 services, such as IES or VPRN, the ARP packets are always examined so no further conditions are applicable.
If an IPv6 static host MAC is not specified the system learns the MAC address depending on the type of host configured such as: IPv6 prefix host or IPv6 address host.
A SAP can be specified as a single-MAC and it implies that there is only a single device attached to the SAP. It changes the MAC learning behavior on the SAP for IPv6 host only. Firstly, all IPv6 hosts shares the same learned MAC. Secondly, the MAC address is learned from the host’s router solicits and neighbor discoveries.
For static host with an address, upon shutdown, a RS for the clients IPv6 address is sent toward the host and the MAC is learned upon the RA reply.
For static host with an address, the OAM command can trigger a RS and the MAC is learned from the RA.
For static host with either a prefix or an address, linking the IPv6 host to an IPv4 host copies the IPv4 host MAC address to the IPv6 host and vice versa.
The learned MAC address is handled as a MAC address of static host with explicitly defined mac-address. Meaning:
The MAC address is not aged by the mac-aging or any other aging timers.
The MAC address is not moved to a new SAP as a consequence of relearning event. A relearning event is a learning request for the same MAC address which comes from a new SAP.
The MAC address is not flushed from FDB because of a SAP failure or STP flush messages.
Every time the specified static-host uses a different MAC address in its ARP request, the dynamic MAC learning process is performed. The old MAC address is overwritten by a new MAC address.
The learned MAC address is not made persistent (a static host is not a part of the persistency file). A service discontinuity of such a host could be proportional to its arp-cache timeout.
The following interactions are described:
antispoof (all services)
If a static IP-only host is configured on a specific SAP, then anti-spoof types, IP, NH MAC, and IP MAC are supported. Static hosts for which the MAC address is not known does not have an anti-spoof entry. It is added only after the corresponding MAC has been learned. As a consequence, all traffic generated by the host before the MAC is learned are dropped.
MAC-linking (IES and VPRN service only)
The MAC address can be learned from either the IPv4 or IPv6 host. When learned it is copied over to the host of the other address family.
single-MAC (IES and VPRN service only)
This specifies that there is only one single subscriber (MAC) on the SAP and any ICMP6 message from the SAP can be assumed to be the subscriber MAC address. This does not apply to IPv4 host.
Enhanced Subscriber Management (all services)
ESM is supported in a combination with a static ip-only host. It is assumed that ip-mac antispoofing is enabled. The resources (queues, and so on) are allocated at the time such a host is configured, although they are effectively used only after anti-spoof entry has been installed.
multi-chassis redundancy
The dynamic MAC address learning event is not synchronized in MCS. When an IP-only static host is configured on both chassis of a redundant BNG pair, MAC learning needs to be triggered on each router independently.
mac-pinning (for VPLS services only)
The dynamically learned MAC address of the static-host is considered as a static-mac and is not affected by the no mac-pinning command.
arp-reply-agent (VPLS services only)
It is possible to the enable arp-reply-agent on a SAP where the static host has ip-only configured. In addition to the regular arp-reply-agent functionality (the reply to all arp-requests targeting the specified host's IP address) learning of the host's MAC address is performed. As long as no MAC address have been learned no ARP replies on behalf of such host should be expected. Enabling of arp-reply-agent is optional for SAP with ip-only static hosts.