Extended LDP Messaging Structure for Multi-AS Routing

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Solution Overview

Problem

In multi-autonomous system (AS) topologies, existing label distribution protocol (LDP) signaled label-switched paths (LSPs) require information about remote AS prefixes or host addresses to be injected into the local interior gateway protocol (IGP), which is undesirable and inefficient, especially in multi-provider scenarios where service providers may not want to advertise peer addresses.

Innovation Solution

Decoupling the forwarding equivalency class (FEC) element from routing information and specifying a next hop, using an extended LDP messaging structure that includes a label, FEC information, and next hop information, allowing nodes to determine whether to propagate LSPs based on next hop information rather than FEC information, thereby avoiding the need to inject remote AS information into the local IGP.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If LDP signaling is used in multi-AS topologies, then LSP establishment is enabled, but remote AS prefix information must be injected into local IGP which increases routing table overhead and reduces scalability

Engineering Contradiction:

ImproveLSP establishment capabilityVSAvoidrouting table overhead

Core Design Contradiction:

Adaptability or versatilityVSQuantity of substance

Solution Approach 1:

The patent segments the LDP message structure into distinct components: a next-hop identifier field that carries the immediate next-hop address, and a separate FEC element that carries the remote AS prefix information. This segmentation allows routers to process and forward LSP signaling without requiring the entire remote AS routing table to be injected into the local IGP, thereby reducing routing table overhead while maintaining LSP establishment capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a next-hop identifier as an intermediary element in the LDP signaling process. This next-hop identifier acts as a mediator that bridges the local router and the remote AS prefix, allowing the router to forward LSP signaling to the correct next-hop address without needing to resolve or inject the complete remote AS routing information into the local IGP table.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If remote AS prefix information is injected into local IGP, then LDP LSP signaling can proceed, but it creates inefficiency in multi-provider scenarios where service providers do not want to advertise peer addresses

Engineering Contradiction:

ImproveLDP signaling operationVSAvoidinformation leakage to external AS

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the next-hop identifier information from the traditional LDP FEC element and places it in a separate dedicated field. This extraction allows the LDP signaling to proceed using only the necessary next-hop address information, while the remote AS prefix information remains separate and is not injected into the local IGP, thereby preventing information leakage to external autonomous systems.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent applies local quality by making the LDP message structure adaptable to local requirements. The next-hop identifier field allows each autonomous system to process LSP signaling with locally relevant information only, while external AS prefix information is handled separately and not propagated into the local IGP, thus maintaining information security boundaries between providers.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If traditional LDP FEC elements are used, then routing information is carried, but it requires exact match with routing table entries which limits flexibility

Engineering Contradiction:

Improverouting match precisionVSAvoidLSP signaling flexibility

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent introduces dynamics by making the LDP message structure flexible and adaptable. The separation of the next-hop identifier from the FEC element allows the system to dynamically select between exact match routing (using traditional FEC) and next-hop based forwarding (using the new identifier), providing versatility in different routing scenarios without sacrificing precision when exact matching is required.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS8176201B1Controlling the signaling of label-switched paths using a label distribution protocol employing messages which facilitate the use of external prefixes

Publication Date: 2012.05.08 JUNIPER NETWORKS INC

AI summary

Label distribution protocol (LDP) signaled label-switched paths (LSPs) are supported without requiring information about remote autonomous systems (ASs) to be injected into the local interior gateway protocol (IGP). This may be done by (i) decoupling a forwarding equivalency class (FEC) element from the routing information, and (ii) specifying a next hop on which the FEC relies. An LDP messaging structure (e.g., an LDP type-length-value (TLV)) that includes a label, FEC information (e.g., a host address or prefix of an egress LSR of the LSP) and a next hop (e.g., a host address or prefix of a border node, such as an AS border router (ASBR)) may be provided. This messaging structure may be included in one or more of (a) label mapping messages, (b) label withdraw messages, and (c) label release messages. If an LDP message including the expanded LDP messaging structure is received at a node, the node may determine whether or not to propagate the LSP using the next hop information, rather than the FEC information. If, on the other hand, the LDP message includes a normal LDP messaging structure, the node may determine whether or not to propagate the LSP as usual.