BFD for Geneve

"Generic Network Virtualization Encapsulation" (Geneve) provides an encapsulation scheme that allows building an overlay network by decoupling the address space of the attached virtual hosts from that of the network. This document describes the use of Bidirectional Forwarding Detection (BFD) protocol to enable monitoring continuity of the path between two Geneve tunnel endpoints, which may be NVE (Network Virtualization Edge) or other device acting as a Geneve tunnel endpoint. For simplicity, in this document, NVE is used to represent Geneve tunnel endpoint, Virtual Machine (VM) is used to represent the device attached to a Geneve tunnel endpoint from the outside. The use cases and the deployment of BFD for Geneve are consistent with what's described in Section 1 and Section 3 of . The major difference between Geneve and "Virtual eXtensible Local Area Network" (VXLAN) encapsulation is that Geneve supports multi-protocol payload and variable length options.

BFD: Bidirectional Forwarding Detection CC: Continuity Check GAL: Generic Associated Channel Label G-ACh: Generic Associated Channel Geneve: Generic Network Virtualization Encapsulation MPLS: Multiprotocol Label Switching NVE: Network Virtualization Edge VM: Virtual Machine VNI: Virtual Network Identifier VXLAN: Virtual eXtensible Local Area Network

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Concerning whether or not the Geneve data packets include an IP protocol data unit, and whether or not the Geneve data packets include an MPLS protocol data unit, this document considers four options of BFD packet encapsulation in Geneve.

If the Protocol Type field (as defined in Section 3.4 of ) of data packets indicates that there exists an inner Ethernet header, i.e., the Protocol Type equals to 0x6558 (Ethernet frame), then BFD packets are encapsulated in Geneve as described below. The Geneve packet format over IPv4 is defined in Section 3.1 of . The Geneve packet format over IPv6 is defined in Section 3.2 of . The Outer IP/UDP and Geneve headers MUST be encoded by the sender as defined in . Note that the outer IP header and the inner IP header may not be of the same address family, in other words, outer IPv6 header accompanied with inner IPv4 header and outer IPv4 header accompanied with inner IPv6 header are both possible.

The BFD packet MUST be carried inside the inner Ethernet frame of the Geneve packet, as specified in Section 4 of . When the BFD packets are encapsulated in Geneve in this way, the Geneve header follows the value set below.

Opt Len field SHOULD be set to 0, which indicates there isn't any variable length option. [Ed.Note]: Use of O bit is still being discussed in the NVO3 WG, so the value is undetermined. C bit MUST be set to 0. Protocol Type field MUST be set to 0x6558 (Ethernet frame).

If the Protocol Type field (as defined in Section 3.4 of ) of data packets indicates that there exists an inner IP header, i.e., the Protocol Type equals to 0x0800 (IPv4) or 0x86DD (IPv6), then BFD packets are encapsulated in Geneve as described below. The Geneve packet format over IPv4 is defined in Section 3.1 of . The Geneve packet format over IPv6 is defined in Section 3.2 of . The Outer IP/UDP and Geneve headers MUST be encoded by the sender as defined in . Note that the outer IP header and the inner IP header may not be of the same address family, in other words, outer IPv6 header accompanied with inner IPv4 header and outer IPv4 header accompanied with inner IPv6 header are both possible.

The BFD packet MUST be carried inside the inner IP packet of the Geneve packet. The inner IP packet carrying the BFD payload has the following format: IP header: Source IP: IP address of the VM-facing interface of the originating NVE. Destination IP: IP address of the VM-facing interface of the terminating NVE. TTL: MUST be set to 1 to ensure that the BFD packet is not routed within the L3 underlay network. The fields of the UDP header and the BFD control packet are encoded as specified in . When the BFD packets are encapsulated in Geneve in this way, the Geneve header follows the value set below. Opt Len field SHOULD be set to 0, which indicates there isn't any variable length option. [Ed.Note]: Use of O bit is still being discussed in the NVO3 WG, so the value is undetermined. C bit MUST be set to 0. Protocol Type field MUST be set to 0x0800 (IPv4) or 0x86DD (IPv6), depending on the address family of the inner IP packet.

If the Protocol Type field (as defined in Section 3.4 of ) of data packets indicates that there exists an inner MPLS header, i.e., the Protocol Type equals to 0x8847 (MPLS) or 0x8848 (MPLS with the upstream-assigned label), then BFD packets are encapsulated in Geneve as described below. The Geneve packet format over IPv4 is defined in Section 3.1 of . The Geneve packet format over IPv6 is defined in Section 3.2 of . The Outer IP/UDP and Geneve headers MUST be encoded by the sender as defined in .

The BFD packet MUST be carried inside the inner MPLS packet of the Geneve packet. The inner MPLS packet carrying the BFD payload has the following format: MPLS Interface Context Label: This Label would be used to identify the VM-facing interface of the originating NVE and the VM-facing interface of the terminating NVE. MPLS GAL(Generic Associated Channel Label): Label value: MUST be set to 13, as specified in . S bit: MUST be set to 1. TTL: MUST be set to 1. The fields of the MPLS G-ACh(Generic Associated Channel) and the BFD control packet are encoded as specified for MPLS-TP CC(Continuity Check) message in . When the BFD packets are encapsulated in Geneve in this way, the Geneve header follows the value set below. Opt Len field SHOULD be set to 0, which indicates there isn't any variable length option. [Ed.Note]: Use of O bit is still being discussed in the NVO3 WG, so the value is undetermined. C bit MUST be set to 0. Protocol Type field MUST be set to 0x8847 (MPLS).

Also, if the BFD control packet is encapsulated in Geneve without the use of IP/UDP header or MPLS G-ACh header, the BFD control packet MAY be identified through the Geneve OAM shim. The layout of the Ethernet frame is shown in . Protocol Type field MUST be set to the value which indicates a Geneve OAM shim that will have a field to indicate the inner BFD control packet. The value of the Protocol Type field and the format of the Geneve OAM shim are defined in . The Geneve OAM shim immediately follows the Geneve header, and the BFD control packet immediately follows the Geneve OAM shim.

Once a packet is received, NVE MUST validate the packet as described in . If the Protocol Type field equals 0x0800 (IPv4) or 0x86DD (IPv6), and the Destination IP of the inner IP packet matches the VM-facing interface IP address of the NVE, the UDP destination port and the TTL of the inner IP packet MUST be validated to determine whether the received packet can be processed by BFD. BFD packet with inner IP set to NVE MUST NOT be forwarded to VMs. If the Protocol Type field equals 0x8847 (MPLS), the MPLS Interface Context Label, the MPLS GAL and the MPLS G-ACh of the inner MPLS packet MUST be validated to determine whether the received packet can be processed by BFD. BFD packet with MPLS GAL MUST NOT be forwarded to VMs. If the Protocol Type field equals 0x8902 which indicates a Geneve OAM shim that will have a field to indicate the inner BFD control message, as specified in , the received packet MUST be processed by BFD and MUST NOT be forwarded to VMs.

Since multiple BFD sessions may be running between two NVEs, and multiple BFD sessions may be originating or terminating at one NVE, there needs to be a mechanism for demultiplexing received BFD packets to the proper session. If the BFD packet is received with Your Discriminator equals to 0, for different BFD encapsulation, the procedure for demultiplexing the received BFD packets is different. When the BFD Encapsulation With Inner Ethernet/IP/UDP Header is used, the BFD session MUST be identified using the procedure specified in Section 5.1 of . When the BFD Encapsulation With Inner IP/UDP Header is used, the BFD session MUST be identified using the inner IP/UDP header, i.e., the source IP and the destination IP present in the inner IP/UDP header. When the BFD Encapsulation With Inner MPLS Header is used, the BFD session MUST be identified using the inner MPLS header, i.e., the MPLS Interface Context Label present in the inner MPLS header. When the BFD Encapsulation With Inner OAM Shim is used, the procedure for demultiplexing the received BFD packets to the proper session is for further study. If the BFD packet is received with non-zero Your Discriminator, then BFD session MUST be demultiplexed only with Your Discriminator as the key. With respect to BFD for Geneve, the use of the specific VNI would follow the principle as specified in Section 6 of .

This document does not raise any additional security issues beyond those of the specifications referred to in the list of normative references.

This document has no IANA action requested.

The authors would like to acknowledge Reshad Rahman, Jeffrey Haas and Matthew Bocci for their guidance on this work.