It is possible for MPLS-TP paths to use both numbered IP numbered interfaces that use ARP/static ARP, or IP unnumbered interfaces. MPLS-TP requires no changes to these interfaces. It is also possible to use a new type of interface that does not require any IP addressing or next-hop resolution.
Draft-ietf-mpls-tp-next-hop-addressing provides guidelines for the usage of various Layer 2 next-hop resolution mechanisms with MPLS-TP. If protocols such as ARP are supported, then they should be used. However, in the case where no dynamic next hop resolution protocol is used, it should be possible to configure a unicast, multicast or broadcast next-hop MAC address. The rationale is to minimize the amount of configuration required for upstream nodes when downstream interfaces are changes. A default multicast MAC address for use by MPLS-TP point-to-point LSPs has been assigned by IANA (Value: 01-00-5e-90-00-00). This value is configurable on the 7210 to support interoperability with 3rd party implementations that do not default to this value, and this no default value is implemented on the 7210.
To support these requirements, a new interface type known as an unnumbered MPLS-TP interface is introduced. This is an unnumbered interface that allows a broadcast or multicast destination MAC address to be configured. An unnumbered MPLS-TP interface is configured using the unnumbered-mpls-tp keyword, as follows.
config
router
interface <if-name> [unnumbered-mpls-tp]
port <port-id>[:encap-val]
mac <local-mac-address>
static-arp <remote-mac-addr>
//ieee-address needs to support mcast and bcast
exit
The remote-mac-address may be any unicast, broadcast of multicast address. However, a broadcast or multicast remote-mac-address is only allowed in the static-arp command on Ethernet unnumbered interfaces when the unnumbered-mpls-tp keyword has been configured. This also allows the interface to accept packets on a broadcast or any multicast MAC address. If a packet is received with a unicast destination MAC address, then it will be checked against the configured <local-mac-address> for the interface, and dropped if it does not match. When an interface is of type unnumbered-mpls-tp, only MPLS-TP LSPs are allowed on that interface; other protocols are blocked from using the interface.
An unnumbered MPLS-TP interface is assumed to be point-to-point, and therefore users must ensure that the associated link is not broadcast or multicast in nature if a multicast or broadcast remote MAC address is configured.
The following is a summary of the constraints of an unnumbered MPLS-TP interface:
It is unnumbered and may borrow/use the system interface address
It prevents explicit configuration of a borrowed address
It prevents IP address configuration
It prevents all protocols except MPLS
It prevents Deletion if an MPLS-TP LSP is bound to the Interface
It is allowed only in network chassis mode D
MPLS-TP is only supported over Ethernet ports. The system will block the association of an MPLS-TP LSP to an interface whose port is non-Ethernet.