RFC 8379
OSPF Graceful Link Shutdown
OSPF Graceful Link Shutdown 🎀
RFC 8379 💖 is from the Internet Engineering Task Force (IETF) 🌸
- Authors: S. Hegde (Juniper Networks, Inc.), P. Sarkar (Arrcus, Inc.), H. Gredler (RtBrick Inc.), M. Nanduri (ebay Corporation), and L. Jalil (Verizon) 👑
- Category: Standards Track 🦋
- ISSN: 2070-1721
- Date: May 2018 📅
- Obsoletes/Updates: the header doesn't list any RFCs this one obsoletes or updates 🙈
Abstract 💖
okay bestie, so when a link is about to be taken out of service, the traffic has to be moved away from both ends of it 🫶. Bumping the metric to the highest value on one side isn't enough, because the traffic flowing the other way still isn't diverted 😭.
It's really useful for routers in an OSPFv2 or OSPFv3 routing domain to advertise a link as being in a graceful-shutdown state ✨. That's how they signal that maintenance is coming up on the link 🔧. Network devices can use that info to reroute traffic effectively 🦋.
This document describes the protocol extensions that spread graceful-link-shutdown information around in OSPFv2 and OSPFv3 💅.
Status of This Memo 🎀
This is an Internet Standards Track document 👑.
This document is a product of the Internet Engineering Task Force (IETF) 🌈. It represents the consensus of the IETF community ✨. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG) 💅. If you want more info on Internet Standards, check Section 2 of RFC 7841 🧚.
Info about the current status of this document, any errata, and how to give feedback on it lives at https://www.rfc-editor.org/info/rfc8379 🔗.
Copyright Notice 🌈
Copyright (c) 2018 IETF Trust and the persons identified as the document authors 💜. All rights reserved 🫶.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info), as they stand on the date this document was published 📜. Please read those carefully, because they spell out your rights and restrictions for this document 🙈. Code Components pulled out of this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions 💅. They come without warranty, as described in the Simplified BSD License ⚠️.
Table of Contents 📑
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Flooding Scope . . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 4
4.1. OSPFv2 Graceful-Link-Shutdown Sub-TLV . . . . . . . . . . 4
4.2. Remote IPv4 Address Sub-TLV . . . . . . . . . . . . . . . 4
4.3. Local/Remote Interface ID Sub-TLV . . . . . . . . . . . . 5
4.4. OSPFv3 Graceful-Link-Shutdown Sub-TLV . . . . . . . . . . 6
4.5. BGP-LS Graceful-Link-Shutdown TLV . . . . . . . . . . . . 6
4.6. Distinguishing Parallel Links . . . . . . . . . . . . . . 7
5. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 8
5.1. Point-to-Point Links . . . . . . . . . . . . . . . . . . 8
5.2. Broadcast/NBMA Links . . . . . . . . . . . . . . . . . . 9
5.3. Point-to-Multipoint Links . . . . . . . . . . . . . . . . 10
5.4. Unnumbered Interfaces . . . . . . . . . . . . . . . . . . 10
5.5. Hybrid Broadcast and P2MP Interfaces . . . . . . . . . . 10
6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 10
7. Applications . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Overlay Network . . . . . . . . . . . . . . . . . . . . . 11
7.2. Controller-Based Deployments . . . . . . . . . . . . . . 12
7.3. L3VPN Services and Sham Links . . . . . . . . . . . . . . 13
7.4. Hub and Spoke Deployment . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 16
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 171. Introduction ✨
okay so this document describes a way to gracefully take a link out of service 🦋, while still letting it carry traffic if no other path is available 🫶. It also gives you a way to divert traffic from both directions of the link 💅.
Lots of OSPFv2 or OSPFv3 deployments run on overlay networks that are set up with pseudowires or L2 circuits 🌸. Before devices in the underlying network go offline for maintenance, it's really helpful to move traffic away from the node first 🙈. The nodes in the underlying network aren't visible to OSPF, so the existing stub-router mechanism in [RFC6987] can't be used here 💀. In a service provider's network there can be tons of CE-to-CE connections running over one PE 😭. Changing the metric on every one of those CE-to-CE connections in both directions is a huge hassle 🥴. This document gives you a way to change the metric of the link on the remote side, and it also lets you use the link as a last-resort link if no alternate paths exist 👑. The use case this is built for is described in detail in Section 7.1 🧚.
This document gives you mechanisms to advertise graceful-link-shutdown state using the flexible encodings from "OSPFv2 Prefix/Link Attribute Advertisement" [RFC7684] and the E-Router-LSA [RFC8362] for OSPFv3 🌈. Throughout this document, "OSPF" is used when the text applies to both OSPFv2 and OSPFv3 💜. "OSPFv2 or OSPFv3" is used when the text is about one specific version 🎀.
1.1. Requirements Language 📜
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here 💅.
2. Motivation 🌟
The whole point of this document is to cut down on manual intervention during maintenance 🧹. These objectives help make that happen across a bunch of different deployment scenarios ✨.
- Advertise impending maintenance so traffic from both directions can be diverted away from the link 🦋.
- Keep the solution backward compatible, so nodes that don't understand the new advertisement don't cause routing loops 🫶.
- Advertise the maintenance to other nodes in the network, so Label Switched Path (LSP) ingress routers or controllers can find out about it and apply specific policies to reroute LSPs in Traffic Engineering (TE) deployments 👑.
- Let the link be used as a last-resort link so traffic doesn't get disrupted when alternate paths aren't available 🧚.
3. Flooding Scope 🌊
The graceful-link-shutdown info gets flooded in an area-scoped Extended Link Opaque LSA [RFC7684] for OSPFv2, and in an E-Router-LSA for OSPFv3 [RFC8362] 💖. The Graceful-Link-Shutdown sub-TLV MAY be processed by the head-end nodes or the controller, as described in the Section 7 ✨. The procedures for processing the Graceful-Link-Shutdown sub-TLV are in Section 5 🎀.
4. Protocol Extensions 🧚
4.1. OSPFv2 Graceful-Link-Shutdown Sub-TLV 🚦
The Graceful-Link-Shutdown sub-TLV says the link is gracefully shutting down 🔧. It's advertised in the Extended Link TLV of the Extended Link Opaque LSA, as defined in [RFC7684] 📡.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Graceful-Link-Shutdown Sub-TLV for OSPFv2Type: 7Length: 0
4.2. Remote IPv4 Address Sub-TLV 🌍
This sub-TLV tells you the IPv4 address of the remote endpoint on the link 💜. It's advertised in the Extended Link TLV, as defined in [RFC7684] ✨. This sub-TLV is optional and MAY be advertised in an area-scoped Extended Link Opaque LSA, to identify the link when there are multiple parallel links between two nodes 🫶.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Remote IPv4 Address Sub-TLVType: 8Length: 4Value: Remote IPv4 address.The remote IPv4 address helps pin down a particular link on the far side when there are multiple parallel links between two nodes 🎀.
4.3. Local/Remote Interface ID Sub-TLV 🦋
This sub-TLV specifies the Local and Remote Interface IDs 💅. It's advertised in the Extended Link TLV, as defined in [RFC7684] 📡. This sub-TLV is optional and MAY be advertised in an area-scoped Extended Link Opaque LSA, to identify the link when there are multiple parallel unnumbered links between two nodes 🌸. The Local Interface ID is generally easy to get 🫶. One of the ways to obtain the Remote Interface ID is described in [RFC4203] 🧠.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Local/Remote Interface ID Sub-TLVType: 9Length: 8Value: 4 octets of the Local Interface ID followed by 4 octets of the Remote Interface ID.💜
4.4. OSPFv3 Graceful-Link-Shutdown Sub-TLV 🌸
okay so the Graceful-Link-Shutdown sub-TLV lives inside the Router-Link TLV from [RFC8362] for OSPFv3 💅 and the Router-Link TLV carries the Neighbor Interface ID, which means it can pinpoint the exact link on the remote node. so precise, I'm obsessed 😭
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Graceful-Link-Shutdown Sub-TLV for OSPFv3
the Type is Type: 8 and the Length is Length: 0 🧚
4.5. BGP-LS Graceful-Link-Shutdown TLV 🦋
BGP-LS, defined in [RFC7752], is the mechanism that shares network info with external entities over BGP 🌐 Graceful link shutdown is important link info those external entities can use for a bunch of different use cases, which are covered in Section 7. The BGP Link Network Layer Reachability Information (NLRI) is what carries the link info. A brand new TLV called "Graceful-Link-Shutdown" describes the link attribute for the graceful-link-shutdown state. The TLV format follows Section 3.1 of [RFC7752]. There's no Value field, and the Length field is set to zero for this one 🫶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Graceful-Link-Shutdown TLV for BGP-LS
the Type is Type: 1121 and the Length is Length: 0 💜
4.6. Distinguishing Parallel Links 🔥
this part is a little bit of a puzzle, bestie 🧩
++++++++++I.w I.y+++++++++++
| Router A | ------------------ | Router B |
++++++++++I.x I.z+++++++++++
Figure 6: Parallel Links
so picture two routers, A and B, joined by two parallel point-to-point interfaces 👯 I.w and I.x are the interface addresses on Router A's side, and I.y and I.z are the interface addresses on Router B's side. The Extended Link Opaque LSA from [RFC7684] describes links using Link Type, Link ID, and Link Data. For example, the link with address I.w looks like this on Router A:
Link Type = Point-to-point
Link ID = Router ID of B
Link Data = I.where's the issue 🙈 a third node (a controller or head-end) can't tell which interface on Router B is connected to this particular Interface on Router A, just from that info. So I.y or I.z could get picked by mistake 😬 In cases like this, a Remote IPv4 Address sub-TLV should be originated and added to the Extended Link TLV. The use cases in Section 7 need controller or head-end nodes to read the graceful-link-shutdown info, which is exactly why the Remote IPv4 Address sub-TLV matters. I.y is carried in the Extended Link TLV, and that unambiguously identifies the interface on the remote side ✨ For OSPFv3, the Router-Link TLV from [RFC8362] has an Interface ID and a neighbor's Interface ID, which can uniquely identify the connecting interface on the remote side. So OSPFv3 doesn't need a separate remote IPv6 address advertised alongside the OSPFv3 Graceful-Link-Shutdown sub-TLV. no extra address needed, periodt 💅
5. Elements of Procedure 👑
okay this is the main event, so pay attention 🎀 As defined in [RFC7684], every link on the node gets its own Extended Link Opaque LSA. The node that has the link being taken out of service MUST advertise the Graceful-Link-Shutdown sub-TLV in the Extended Link TLV of the Extended Link Opaque LSA for OSPFv2, as defined in [RFC7684], and in the Router-Link TLV of E-Router-LSA for OSPFv3. The sub-TLV basically says "this link is getting maintenance" 🔧
for changing the metric, OSPFv2 and OSPFv3 Router-LSAs need to be reoriginated. And to change the Traffic Engineering metric, TE Opaque LSAs in OSPFv2 [RFC3630] and Intra-area-TE-LSAs in OSPFv3 [RFC5329] need to be reoriginated 🔁
the graceful-link-shutdown info is advertised as a property of the link and gets flooded through the area 🌊 Ingress routers or controllers can use it to take special actions. There's an application built for this use case in Section 7.2 ✨
when the link is ready to carry traffic again, the Graceful-Link-Shutdown sub-TLV MUST be removed from the Extended Link TLV/Router-Link TLV, and the corresponding LSAs MUST be readvertised. Same deal for the metric: it MUST be set back to its original values, and the corresponding LSAs MUST be readvertised 🌈
the procedures in this document can also be used to divert traffic away from a link in situations other than link-shutdown or link-replacement activity 🦋
and what the remote node at the other end does depends on the link type 👀
5.1. Point-to-Point Links 💖
the node that has the link being taken out of service MUST set the metric of the link to MaxLinkMetric (0xffff) and reoriginate its Router-LSA 🚦 The Traffic Engineering metric of the link SHOULD be set to (0xffffffff), and the node SHOULD reoriginate the corresponding TE Link Opaque LSAs. When a Graceful-Link-Shutdown sub-TLV is received for a point-to-point link, the remote node MUST identify the local link that corresponds to the graceful-shutdown link and set its metric to MaxLinkMetric (0xffff). The remote node MUST reoriginate its Router-LSA with the changed metric. When TE is enabled, the Traffic Engineering metric of the link SHOULD be set to (0xffffffff) and follow the procedures in [RFC5817]. Similarly, the remote node SHOULD set the Traffic Engineering metric of the link to 0xffffffff and SHOULD reoriginate the TE Link Opaque LSA for the link with the new value 🫶
the Extended Link Opaque LSAs and the Extended Link TLV are not scoped for multi-topology [RFC4915]. In multi-topology deployments [RFC4915], the Graceful-Link-Shutdown sub-TLV advertised in an Extended Link Opaque LSA applies to all the topologies that include the link. The receiver node SHOULD change the metric in the reverse direction for all the topologies that include the remote link, and reoriginate the Router-LSA as defined in [RFC4915] 🌐
when the originator of the Graceful-Link-Shutdown sub-TLV purges the Extended Link Opaque LSA, or reoriginates it without the Graceful-Link-Shutdown sub-TLV, the remote node must reoriginate the appropriate LSAs with the metric and TE metric values set back to their original values 🔄
5.2. Broadcast/NBMA Links 🌟
broadcast or Non-Broadcast Multi-Access (NBMA) networks in OSPF look like a star ⭐ The Designated Router (DR) is the central point that every other router on the network logically connects to. So routers on the network only advertise their adjacency to the DR, and the non-DR routers don't form or advertise adjacencies with each other. For broadcast links, the MaxLinkMetric on the remote link can't be changed, since all the neighbors sit on the same link. Setting the link cost to MaxLinkMetric would hit every path that goes through any of the neighbors on that broadcast link 😱
the node that has the link being taken out of service MUST set the metric of the link to MaxLinkMetric (0xffff) and reoriginate the Router-LSA. The Traffic Engineering metric of the link SHOULD be set to (0xffffffff), and the node SHOULD reoriginate the corresponding TE Link Opaque LSAs. For a broadcast link, the two-part metric from [RFC8042] is used. The node originating the Graceful-Link-Shutdown sub-TLV MUST set the metric in the Network-to-Router Metric sub-TLV to MaxLinkMetric (0xffff) for OSPFv2 and OSPFv3, and reoriginate the corresponding LSAs. Nodes that receive the two-part metric should follow the procedures described in [RFC8042]. The backward-compatibility procedures described in [RFC8042] should be followed to keep routing loop-free 🔁
5.3. Point-to-Multipoint Links 🦋
P2MP operation is pretty similar to point-to-point links 💕 When a Graceful-Link-Shutdown sub-TLV is received for a point-to-multipoint link, the remote node MUST identify the neighbor that corresponds to the graceful-shutdown link and set its metric to MaxLinkMetric (0xffff). The remote node MUST reoriginate the Router-LSA with the changed metric for that corresponding neighbor 🎯
5.4. Unnumbered Interfaces 🧚
unnumbered interfaces don't have a unique IP address and borrow one from other interfaces 🫠 [RFC2328] describes how to handle unnumbered interfaces in the context of the Router-LSA. We use a similar approach for the Extended Link TLV advertising the Graceful-Link-Shutdown sub-TLV, so unnumbered interfaces get handled too. The Link-Data field in the Extended Link TLV carries the Local Interface ID instead of an IP address. The Local/Remote Interface ID sub-TLV MUST be advertised when there are multiple parallel unnumbered interfaces between two nodes ‼️ One of the ways to get the Interface ID of the remote side is defined in [RFC4203] 🌸
5.5. Hybrid Broadcast and P2MP Interfaces 🍓
hybrid Broadcast and P2MP interfaces are a broadcast network modeled as P2MP interfaces 🤯 [RFC6845] describes how to handle these. Operation for hybrid interfaces is pretty much the same as for P2MP interfaces. When a Graceful-Link-Shutdown sub-TLV is received for a hybrid link, the remote node MUST identify the neighbor that corresponds to the graceful-shutdown link and set its metric to MaxLinkMetric (0xffff). Every remote node connected to the originator MUST reoriginate the Router-LSA with the changed metric for that neighbor 💜
6. Backward Compatibility 🫶
the mechanisms in this document are fully backward compatible 🥰 For traffic to actually get diverted off the graceful-shutdown link, both the node advertising the Graceful-Link-Shutdown sub-TLV and the node at the remote end of that link are required to support the extensions described here. If the remote node doesn't support the capability, it'll still use the graceful-shutdown link, but there are no other adverse effects 🙏 For broadcast links using two-part metrics, the backward-compatibility procedures in [RFC8042] apply too.
7. Applications 🌈
7.1. Overlay Network ✨
Okay so, lots of service providers sell L2 services that connect a customer's different locations 🌸 The customer's IGP makes one seamless private network (an overlay network) across all those sites. Now here's the drama: providers want graceful-shutdown vibes when a PE device has to go in for maintenance 💅 A single PE can have a ton of customers hanging off it, and the far ends of those L2 attachment circuits are scattered all over the provider's network. Changing the metric on every one of those circuits, in both directions? Tedious and so easy to mess up 😭 That's where graceful-link-shutdown comes in and saves the day 🦋 It raises the metric on the CE-CE overlay link so traffic in both directions gets pulled away from the PE that's getting maintenance. It's also giving "last resort," because the link can still be used when no other path exists, so traffic doesn't get disrupted 🫶
Here's the picture:
------PE3---------------PE4------CE3
/ \
/ \
CE1---------PE1----------PE2---------CE2
\
\
------CE4CE: Customer Edge PE: Provider Edge
Figure 7: Overlay Network
So in Figure 7, PE1 is about to go offline for maintenance 🔧 The provider puts PE1 into stub-router state and tells the overlay customers about the upcoming work 📣 How PE1 and CE1 talk about it is outside the scope of this document, so we're not getting into that 🙈 Then CE1 sets the graceful-link-shutdown state on its links to CE3, CE2, and CE4, changes the metric to MaxLinkMetric, and reoriginates the corresponding LSA ✨ The far end of those links at CE3, CE2, and CE4 also sets the metric on the link to MaxLinkMetric, and boom, traffic from both directions gets diverted away from PE1 💜
7.2. Controller-Based Deployments 🎀
Now picture deployments where a controller is actually part of the IGP 👑 The controller can get the graceful-link-shutdown info too, which is basically an early warning that link maintenance is coming up ⭐ With that heads-up, the controller can hunt down alternate paths for the traffic using the affected link 🧚 It can apply different policies and reroute the LSPs away from the link under maintenance 🦋 And if there aren't any alternate paths that meet the constraints? The controller might temporarily relax those constraints and park the service on a different path 💅
Also, plain metric increases aren't enough to tell you about maintenance, because metrics can go up for other reasons too, like LDP-IGP synchronization 🙈 So an explicit signal is needed: the router sends the Graceful-Link-Shutdown sub-TLV to tell the controller or head-end routers what's actually going on 🫶
_____________
| |
--------------| Controller |--------------
| |____________ | |
| |
|--------- Primary Path ------------------|
PE1---------P1----------------P2---------PE2
| |
| |
|________P3________|
Alternate PathFigure 8: Controller-Based Traffic Engineering
Let's walk through this one 🍓 The PE1->PE2 LSP is set up to satisfy a constraint of 10 Gbps bandwidth on each link. The links P1->P3 and P3->P2 only have 1 Gbps capacity, so there's no alternate path that meets the 10 Gbps bandwidth constraint 😭 When the P1->P2 link gets prepped for maintenance, the controller gets the graceful-link-shutdown info. Since no alternate path satisfies the constraints, the controller picks a less optimal path and temporarily sets up an alternate path via P1->P3->P2 🌈 Once the traffic has moved over, the P1->P2 link can finally go out of service for its maintenance or upgrade ✨
7.3. L3VPN Services and Sham Links 🌸
Lots of service providers offer Layer 3 Virtual Private Network (L3VPN) services to customers, and the CE-PE links run OSPF [RFC4577] 💜 When a PE is taken out of service for maintenance, you can set all the links on that PE to graceful-link-shutdown state. That guarantees the traffic to and from dual-homed CEs gets diverted 🦋 How OSPF and BGP interact is outside the scope of this document, so we're skipping that 🙈 There's also a mechanism based on [RFC6987], using summaries and externals advertised with high metrics, that could get you the same result. That only works when implementations support high metrics advertisement for summaries and externals 🫶
Another useful use case: ISPs offering sham-link services to customers [RFC4577] 🧚 When the PE goes out of service for maintenance, you can set all the sham links on that PE to graceful-link-shutdown state. Traffic can then be diverted from both ends without touching the configurations on the remote end of the sham links 🎀
7.4. Hub and Spoke Deployment 🍓
OSPF is hugely deployed in Hub and Spoke setups, with a big pile of Spokes connecting to the Hub 👑 It's common practice to deploy multiple Hubs with every Spoke connecting to all of them, for redundancy 💅 The mechanism defined in [RFC6987] can divert Spoke-to-Spoke traffic away from an overloaded Hub router ✨ Traffic flowing from Spokes via the Hub into an external network may not be diverted in certain scenarios ⭐ When a Hub node goes down for maintenance, you can set all the links on that Hub to graceful-link-shutdown state. Traffic then gets diverted from the Spoke sites too, without making any configuration changes on the Spokes 🌈
8. Security Considerations 🔐
This document utilizes the OSPF packets and LSAs described in [RFC2328] , [RFC3630], [RFC5329], and [RFC5340]. The authentication procedures described in [RFC2328] for OSPFv2 and [RFC4552] for OSPFv3 are applicable to this document as well. This document does not introduce any further security issues other than those discussed in [RFC2328] and [RFC5340].
9. IANA Considerations 🧾
IANA has registered the following in the "OSPFv2 Extended Link TLV Sub-TLVs" registry:
7 - Graceful-Link-Shutdown Sub-TLV
8 - Remote IPv4 Address Sub-TLV
9 - Local/Remote Interface ID Sub-TLVIANA has registered the following value in the "OSPFv3 Extended-LSA Sub-TLVs" registry:
8 - Graceful-Link-Shutdown sub-TLVIANA has registered the following value in the "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" registry [RFC7752]":
1121 - Graceful-Link-Shutdown TLV10. References 📚
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
DOI 10.17487/RFC3630, September 2003,
<https://www.rfc-editor.org/info/rfc3630>.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<https://www.rfc-editor.org/info/rfc5329>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5817] Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton,
"Graceful Shutdown in MPLS and Generalized MPLS Traffic
Engineering Networks", RFC 5817, DOI 10.17487/RFC5817,
April 2010, <https://www.rfc-editor.org/info/rfc5817>.
[RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
and Point-to-Multipoint Interface Type", RFC 6845,
DOI 10.17487/RFC6845, January 2013,
<https://www.rfc-editor.org/info/rfc6845>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8042] Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part
Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016,
<https://www.rfc-editor.org/info/rfc8042>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.10.2. Informative References
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<https://www.rfc-editor.org/info/rfc4203>.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
[RFC4577] Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the
Provider/Customer Edge Protocol for BGP/MPLS IP Virtual
Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577,
June 2006, <https://www.rfc-editor.org/info/rfc4577>.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
RFC 4915, DOI 10.17487/RFC4915, June 2007,
<https://www.rfc-editor.org/info/rfc4915>.Acknowledgements 💖
Thanks to Chris Bowers for valuable input and edits to the document. Thanks to Jeffrey Zhang, Acee Lindem, and Ketan Talaulikar for their input. Thanks to Karsten Thomann for careful review and input on the applications where graceful link shutdown is useful.
Thanks to Alia Atlas, Deborah Brungard, Alvaro Retana, Andrew G. Malis, and Tim Chown for their valuable input. 🫶
Authors' Addresses ✨
okay bestie, this is the squad roster 🫶 these are the five people who wrote the thing, with their addresses and emails so you can actually reach them. no cap, they earned it 💅
Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Pushpasis Sarkar
Arrcus, Inc.
Email: pushpasis.ietf@gmail.com
Hannes Gredler
RtBrick Inc.
Email: hannes@rtbrick.com
Mohan Nanduri
ebay Corporation
2025 Hamilton Avenue
San Jose, CA 98052
United States of America
Email: mnanduri@ebay.com
Luay Jalil
Verizon
Email: luay.jalil@verizon.comand that's the whole doc, babe 🦋✨ the end!! 🎀
📦 where this page comes from
- ietf: rfc8379 2018-05
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms