Using IS-IS To Advertise Power Group Membership

Introduction This document introduces Power Groups. A Power Group is a hierarchical abstraction of power consumed by hardware components. In IS-IS, interfaces can reference the Power Group to which they belong. Therefore, Power Groups provide a method of organizing interfaces into groups by power characteristics. The TE path placement algorithm can use Power Group membership information to implement TE policy. Power Group information is particularly useful when implementing TE policies that support power-savings and sustainability.

Conventions and Definitions 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 BCP14 when, and only when, they appear in all capitals, as shown here.

Example Architecture

Line Card 1 depicts a line card (LC1). LC1 contains two forwarding engines (FE1 and FE2) and four interface complexes (INTCOMP1 through INTCOMP4). INTCOMP1 supports in two interfaces (INT1 and INT2). Likewise, INTCOMP3 supports in two interfaces (INT4 and INT5). INTCOMP2 and INTCOMP4 support one interface each (INT3 and INT6). An interface complex includes PHY, MAC, encryption, gearbox, and other related circuitry. INTCOMP1 and INTCOMP3 also contain optics. INTCOMP2 and INTCOMP4 do not contain optics. Therefore, the interfaces that they support have their own optics. INTCOMP1 and INTCOMP3 provide 400 Gbps of forwarding capacity each, while INCOMP2 and INTCOMP4 provide 800 Gbps of forwarding capacity each. Each hardware component consumes power. LC1 consumes 100 watts while FE1 and FE2 consume 300 watts each. INTCOMP1 and INTCOMP3 consume 15 watts each, while INTCOMP2 and INTCOMP4 consume 20 watts each. INT3 and INT6 contain optics that consume 5 watts each. INT1, INT2, INT4 and INT5 do not do separate optics. Therefore, they do not consume power beyond what is consumed by the complex. INT1 and INT2 depend upon INTCOMP1. If INTCOMP1 fails, so do INT1 and INT2. Likewise, INT3 depends upon INTCOMP2. If INTCOMP2 fails, so does INT3. INTCOMP1 and INTCOMP2 depend on FE1. If FE1 fails, so do INTCOMP1, INTCOMP2, INT1, INT2, and INT3. Likewise, INTCOMP3 and INTCOMP4 depend on FE2. If FE2 fails, so do INTCOMP3, INTCOMP4, INT4, INT5, and INT6. FE1 and FE2 depend on LC1. If LC1 fails, so do all of the forwarding engines, interface complexes, and interfaces in the diagram.

Power Groups A Power Group is a hierarchical abstraction of power consumed by hardware components. Each Power Group, except for the one at the top of the hierarchy, has exactly one parent. The Power Group at the top of the hierarchy does not have a parent. Many Power Groups can have the same parent. Each Power Group has one or more components and each component consumes power. The power consumed by a Power Group is equal to the sum of the power consumed by each of its components. The power consumed by a Power Group does not include the power consumed by its ancestors or by its children. The parent-child relationship reflects dependency. One Power Group is the child of another if any one of the child components depends upon any one of the parent components. A network device's power consumption characteristics can be described by any number of equivalent Power Group hierarchies. The paragraphs below demonstrate how two equivalent Power Group hierarchies can describe the power consumption characteristics of the line card in Figure 1. A Granular Power Group Hierarchy

Identifier	Parent	Power Consumption	Hardware Components
1	None	100 watts	LC1
2	1	300 watts	FE1
3	1	300 watts	FE2
4	2	15 watts	INTCOMP1
5	2	20 watts	INTCOMP2
6	3	15 watts	INTCOMP3
7	3	20 watts	INTCOMP4
8	5	5 watts	INT3
9	7	5 watts	INT6

describes the power consumption characteristics of the line card in using a granular Power Group hierarchy. We call it granular because each Power Group contains only one component. The power consumed by each Power Group is equal to the power consumed by its component. In , Power Group 7 is the child of Power Group 3 because INTCOMP4 depends upon FE2. Likewise, Power Group 3 is the child of Power Group 1 because FE2 depends on LC1. Furthermore, Power Group 8 is the child of Power Group 5 because INT3 depends upon INCOMP2. Likewise, Power Group 9 is the child of Power Group 7 because INT6 depends on INTCOMP4. A Less Granular Power Group Hierarchy

Identifier	Parent	Power Consumption	Hardware Components
1	None	700 watts	LC1, FE1, FE2
2	1	15 watts	INTCOMP1
3	1	20 watts	INTCOMP2
4	1	15 watts	INTCOMP3
5	1	20 watts	INTCOMP4
6	1	5 watts	INT3
7	1	5 watts	INT6

describes the power consumption characteristics of the line card in using a less granular Power Group hierarchy. We call it less granular because Power Group 1 contains three components (LC1, FE1 and FE2). Its power consumption is equal to the sum of the power consumed by LC1, FE1 and FE2 (i.e., 700 watts). Power Group 2 and Power Group 3 are children of Power Group 1 because INTCOMP1 and INTCOMP2 depend on FE1. Likewise, Power Group 4 and Power Group 5 are children of Power Group 1 because INTCOMP3 and INTCOMP4 depend on FE2. Finally, Power Group 5 and Power Group 7 are children of Power Group 1 because INT3 and INT6 depend on INCOMP2 and INCOMP4.. describes how a network device's power-save capability determines which of the equivalent Power Group hierarchies it should advertise. describes how IS-IS advertises Power Group information.

Interfaces and Power Groups An interface is not part of a Power Group, even if it contains optics and consumes power. However, an interface can reference a Power Group. When it references a Power Group, it MUST reference the Power Group that contains the interface complex that supports it. See . Therefore, Power Groups can be used to associate interfaces that depend on a common set of hardware components and have common power consumption characteristics. A Link Aggregation Group (LAG) interface requires support from multiple interface complexes. Therefore a LAG interface references every Power Group that contains an interface complex that supports it. describes how an interface can advertise the power that it consumes.

Power-Save Capability and Power Group Hierarchies A network device SHOULD advertise the least granular Power Group hierarchy that can exercise its complete power-savings capability. Assume that a network contains line cards that are power-save capable. Those line cards contain forwarding engines and interface complexes that are also power-save capable. This means that the line cards, forwarding engines and interface complexes can be powered on and off independently of the chassis. In order to exercise its complete power savings capability, information regarding line card, forwarding engine and interface complex dependencies is required. Therefore, the line card must advertise the granular Power Group hierarchy in . Now assume that another network contains line cards that are power-save capable. Those line cards contain interface complexes that are also power-save capable. However, the forwarding engines are not power-save capable. In order to exercise its complete power savings capability,
information regarding line card, and interface complex dependencies is required. However, information regarding forwarding engine dependencies is not required. Therefore, the line card could advertise either the granular Power Group hierarchy in or the less granular Power Group hierarchy in .

Link State Database Elements

The Power Group TLV The Power Group is a top level TLV that describes a Power Group.

Power Group TLV Where:

Type: 1 octet, value TBD1
Length: 1 octet, unsigned integer. Value 13.
Power Group Identifier: 4 octets, selector. MUST NOT be equal to 0.
Power: 4 octets, unsigned integer. The power consumed by the Power Group, in milliwatts.
Parent Identifier: 4 octets, selector.
C: 1 bit. Indicates that every component in the Power Group is power-save capable.
Reserved: 7 bits. MUST be set to 0 by the sender and MUST be ignored by the receiver.

The Power Group Identifier has node-local significance. If the Parent Identifier is equal to 0, the Power Group has no parent (i.e., it is the root of a Power Group hierarchy). Otherwise, the Parent Identifier MUST NOT be set to 0.

The Sleeping Adjacency TLV The Sleeping Adjacency TLV is a top level TLV. If an adjacency is in the power-sleep mode, the TLVs that represent it appear only in the Sleeping Adjacency TLV. They do not also appear as top-level TLVs. The Sleeping Adjacency TLV can include TLVs 22, 23, 141, 222 and 223.

Sleeping Adjacencies TLV Where:

Type: 1 octet, value TBD2
Length: 1 octet, unsigned integer. The length of the TLV, measured in octets, not including the type and length fields.
Sleeping Adjacencies: A list of adjacency TLVs of type 22, 23, 141, 222 and 223. These TLVs represent adjacencies that are in the power-sleep mode.

Interface Extensions

The Power Group Member Sub-TLV This sub-TLV is found in TLVs for advertising neighbor information. This sub-TLV advertises a Power Group to which the interface belongs. Because a LAG interface can belong to many Power Groups, many instances of this sub-TLV may be advertised.

Power Group Member Sub-TLV Where:

Type: 1 octet, value TBD3
Length: 1 octet, unsigned integer. Value 4,
Power Group Identifier: 4 octets, selector.

The Interface Power Sub-TLV This sub-TLV is found in TLVs for advertising neighbor information. This sub-TLV advertises the power consumed by an interface. A dynamic value might cause unnecessary churn in the Link State Database (LSDB), so a static value should be used.

Interface Power Sub-TLV Where:

Type: 1 octet, value TBD4
Length: 1 octet, unsigned integer. Value 4
Power: 4 octets, unsigned integer. The power consumed by the interface, in milliwatts.

Unidirectional Sleeping Bandwidth Sub-TLV This sub-TLV is found in TLVs for advertising neighbor information. This sub-TLV advertises the sleeping bandwidth between two directly connected IS-IS neighbors. The sleeping bandwidth advertised by this sub-TLV MUST be the sleeping bandwidth from the system originating the Link State Advertisement (LSA) to its neighbor.

Unidirectional Sleeping Bandwidth Sub-TLV Where:

Type: 1 octet, value TBD5
Length: 1 octet, unsigned integer. Value 4.
Sleeping Bandwidth: 4 octets, IEEE floating-point format measured in bytes per second.

The Sleeping bandwidth field carries the sleeping bandwidth on a link, forwarding adjacency , or bundled link. For a link or forwarding adjacency, sleeping bandwidth is defined as the maximum bandwidth minus the bandwidth currently allocated to RSVP-TE label switched paths that was transitioned to power-sleep. For a bundled link, sleeping bandwidth is defined to be the sum of the component link sleeping bandwidths.

The Power-Sleep Capable Bit This is a bit in the Link Attribute Sub-TLV (19). Presence of this bit indicates that the link may be put into power-sleep mode. The position of this bit is TBD5.

Operational Considerations Network operators must exercise care when configuring interfaces to be power-sleep capable. The TE path placement algorithm can use Power Groups to implement TE policies that support power-savings. In this case, the path placement algorithm identifies a Power Group in which all interfaces are power-sleep capable. It then diverts traffic from those interfaces. When traffic has been diverted, power can be removed from every hardware component in the Power Group. Removing power from those components may cause the network to be insufficiently redundant. The subsequent failure of a single link may bisect the network. Therefore, network operators must configure selected interfaces so that they are not power-sleep capable and will never be powered down.

Security Considerations TBD

IANA Considerations IANA is requested to add the following entries to the IS-IS Top-Level TLV Codepoints registry (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#tlv-codepoints): IS-IS Top-Level TLV Codepoints

Value	Name	IIH	LSP	SNP	Purge	MP	Status Reference
TBD1	Power Group	N	Y	N	N	N	This document
TBD2	Sleeping Adjacencies	N	Y	N	N	N	This document

IANA is also requested to add the following entries to the IS-IS Sub-TLVs for TLVs Advertising Neighbor Information registry (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-advertising-neighbor-information): IS-IS Sub-TLVs for TLVs Advertising Neighbor Information

Type	Description	22	23	25	141	222	223	MP	Reference
TBD3	Power Group Member	Y	Y	Y(s)	Y	Y	Y	N	This document
TBD4	Interface Power	Y	Y	Y(s)	Y	Y	Y	N	This document
TBD5	Unidirectional Sleeping Bandwith	Y	Y	Y(s)	Y	Y	Y	N	This document

IANA is also requested to add the following entry to the IS-IS Neighbor Link-Attribute Bit Values registry (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-19of22): IS-IS Neighbor Link-Attribute Bit Values

Value	Name	L2BM	Reference
TBD5	Power-Sleep Capable	N	This document

Acknowledgements TBD