Chapter 18. Transit Fast Restoration Based on the IGP
Fast Restoration Concepts
Before starting a detailed discussion about protection and traffic restoration techniques, let’s clarify the terminology used in this book.
Ingress/Transit/Egress Transport Protection Concepts
Figure 18-1 presents a generic service model with two dual-homed CE devices connected to a service provider (SP) IP/MPLS network. PE nodes provide the service itself (e.g., L3VPN), whereas Provider (P) nodes are used purely for transmitting packets between PE nodes. Additionally, the figure also shows various failure cases (nine in total) that can affect example traffic flow from left CE to right CE.
For the purpose of this book, failure categories (and corresponding protection categories) are classified as follows:
- Ingress protection
- This is an action performed to minimize traffic loss during failure of an ingress CE-PE link (failure case 1) or ingress PE node (failure case 2). The Point of Local Repair (PLR) is the ingress CE, which after detecting failure (based on Loss of Signal [LoS], or OAM, or BFD, etc.) switches the outgoing traffic to another (bottom) PE node.
- Transit protection
- This is an action performed to minimize traffic loss during failure of a transit link (failure case 3, 5, or 7) or transit P node (failure case 4 or 6). The PLR is either the ingress PE node (for failure case 3 or 4) or some transit P node (for failure cases 5, 6, or 7). Different MPLS techniques are available to minimize ...