ECMP

This memo describes per-packet stateless strict and loose path steered replication and forwarding for "Bit Index Explicit Replication" (BIER) packets (RFC 8279); it is called "Tree Engineering for Bit Index Explicit Replication" (BIER-TE) and is intended to be used as the path steering mechanism for Traffic Engineering with BIER.

BIER-TE introduces a new semantic for "bit positions" (BPs). These BPs indicate adjacencies of the network topology, as opposed to (non-TE) BIER in which BPs indicate "Bit-Forwarding Egress Routers" (BFERs). A BIER-TE "packets BitString" therefore indicates the edges of the (loop-free) tree across which the packets are forwarded by BIER-TE. BIER-TE can leverage BIER forwarding engines with little changes. Co-existence of BIER and BIER-TE forwarding in the same domain is possible -- for example, by using separate BIER "subdomains" (SDs). Except for the optional routed adjacencies, BIER-TE does not require a BIER routing underlay and can therefore operate without depending on a routing protocol such as the "Interior Gateway Protocol" (IGP).

Segment Routing (SR) leverages the source-routing paradigm. A node steers a packet through an ordered list of instructions, called segments. Segment Routing can be applied to the Multiprotocol Label Switching (MPLS) data plane. Entropy labels (ELs) are used in MPLS to improve load-balancing. This document examines and describes how ELs are to be applied to Segment Routing MPLS.

The pseudowire (PW) encapsulation of Ethernet, as defined in RFC 4448, specifies that the use of the control word (CW) is optional. In the absence of the CW, an Ethernet PW packet can be misidentified as an IP packet by a label switching router (LSR). This may lead to the selection of the wrong equal-cost multipath (ECMP) path for the packet, leading in turn to the misordering of packets. This problem has become more serious due to the deployment of equipment with Ethernet Media Access Control (MAC) addresses that start with 0x4 or 0x6. The use of the Ethernet PW CW addresses this problem. This document RECOMMENDS the use of the Ethernet PW CW in all but exceptional circumstances.

This document updates RFC 4448.

Some network operators build and operate data centers that support over one hundred thousand servers. In this document, such data centers are referred to as "large-scale" to differentiate them from smaller infrastructures. Environments of this scale have a unique set of network requirements with an emphasis on operational simplicity and network stability. This document summarizes operational experience in designing and operating large-scale data centers using BGP as the only routing protocol. The intent is to report on a proven and stable routing design that could be leveraged by others in the industry.

This document specifies an IP-based encapsulation for MPLS, called MPLS-in-UDP for situations where UDP (User Datagram Protocol) encapsulation is preferred to direct use of MPLS, e.g., to enable UDP-based ECMP (Equal-Cost Multipath) or link aggregation. The MPLS- in-UDP encapsulation technology must only be deployed within a single network (with a single network operator) or networks of an adjacent set of cooperating network operators where traffic is managed to avoid congestion, rather than over the Internet where congestion control is required. Usage restrictions apply to MPLS-in-UDP usage for traffic that is not congestion controlled and to UDP zero checksum usage with IPv6.

Demands on networking infrastructure are growing exponentially due to bandwidth-hungry applications such as rich media applications and inter-data-center communications. In this context, it is important to optimally use the bandwidth in wired networks that extensively use link aggregation groups and equal-cost multipaths as techniques for bandwidth scaling. This document explores some of the mechanisms useful for achieving this.

This document provides guidelines for implementers regarding MPLS forwarding and a basis for evaluations of forwarding implementations. Guidelines cover many aspects of MPLS forwarding. Topics are highlighted where implementers might otherwise overlook practical requirements which are unstated or under emphasized or are optional for conformance to RFCs but are often considered mandatory by providers.

This document provides a set of requirements for Advanced Multipath in MPLS networks.

Advanced Multipath is a formalization of multipath techniques currently in use in IP and MPLS networks and a set of extensions to existing multipath techniques.

Many MPLS implementations have supported multipath techniques, and many MPLS deployments have used multipath techniques, particularly in very high-bandwidth applications, such as provider IP/MPLS core networks. MPLS Transport Profile (MPLS-TP) has strongly discouraged the use of multipath techniques. Some degradation of MPLS-TP Operations, Administration, and Maintenance (OAM) performance cannot be avoided when operating over many types of multipath implementations.

Using MPLS Entropy Labels (RFC 6790), MPLS Label Switched Paths (LSPs) can be carried over multipath links while also providing a fully MPLS-TP-compliant server layer for MPLS-TP LSPs. This document describes the means of supporting MPLS as a server layer for MPLS-TP. The use of MPLS-TP LSPs as a server layer for MPLS LSPs is also discussed.

This document describes how the currently specified IPv6 flow label can be used to enhance layer 3/4 (L3/4) load distribution and balancing for large server farms.

Load balancing is a powerful tool for engineering traffic across a network. This memo suggests ways of improving load balancing across MPLS networks using the concept of "entropy labels". It defines the concept, describes why entropy labels are useful, enumerates properties of entropy labels that allow maximal benefit, and shows how they can be signaled and used for various applications. This document updates RFCs 3031, 3107, 3209, and 5036. [STANDARDS-TRACK]

A Protocol Independent Multicast (PIM) router uses the Reverse Path Forwarding (RPF) procedure to select an upstream interface and router in order to build forwarding state. When there are equal cost multipaths (ECMPs), existing implementations often use hash algorithms to select a path. Such algorithms do not allow the spread of traffic among the ECMPs according to administrative metrics. This usually leads to inefficient or ineffective use of network resources. This document introduces the ECMP Redirect, a mechanism to improve the RPF procedure over ECMPs. It allows ECMP selection to be based on administratively selected metrics, such as data transmission delays, path preferences, and routing metrics. [STANDARDS-TRACK]

Various published proposals for use of the IPv6 flow label are incompatible with its original specification in RFC 3697. Furthermore, very little practical use is made of the flow label, partly due to some uncertainties about the correct interpretation of the specification. This document discusses and motivates changes to the specification in order to clarify it and to introduce some additional flexibility. This document is not an Internet Standards Track specification; it is published for informational purposes.

The IPv6 flow label has certain restrictions on its use. This document describes how those restrictions apply when using the flow label for load balancing by equal cost multipath routing and for link aggregation, particularly for IP-in-IPv6 tunneled traffic. [STANDARDS-TRACK]

This document describes the Equal Cost Multipath (ECMP) behavior of currently deployed MPLS networks. This document makes best practice recommendations for anyone defining an application to run over an MPLS network that wishes to avoid the reordering that can result from transmission of different packets from the same flow over multiple different equal cost paths. These recommendations rely on inspection of the IP version number field in packets. Despite the heuristic nature of the recommendations, they provide a relatively safe way to operate MPLS networks, even if future allocations of IP version numbers were made for some purpose. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.

The effect of multipath routing on a forwarder is that the forwarder potentially has several next-hops for any given destination and must use some method to choose which next-hop should be used for a given data packet. This memo summarizes current practices, problems, and solutions. This memo provides information for the Internet community.

Equal-cost multi-path (ECMP) is a routing technique for routing packets along multiple paths of equal cost. The forwarding engine identifies paths by next-hop. When forwarding a packet the router must decide which next-hop (path) to use. This document gives an analysis of one method for making that decision. The analysis includes the performance of the algorithm and the disruption caused by changes to the set of next-hops. This memo provides information for the Internet community.

VLSP provides support for equal-cost multipath routing, and recalculates routes quickly in the face of topological changes, utilizing a minimum of routing protocol traffic. This memo provides information for the Internet community.