RFC 2973
IS-IS Mesh Groups
Okay bestie, this is RFC 2973 💖 called IS-IS Mesh Groups 🎀. It's dated October 2000 and it's Informational 🦋, so it's sharing info with the Internet community and does not specify an Internet standard. The authors are R. Balay (CoSine Communications), D. Katz (Juniper Networks), and J. Parker (Axiowave Networks) 👑. The title block doesn't list anything it obsoletes or updates 🙈.
Status of this Memo 💅
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited 🌸.
Copyright Notice 🔥
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract ✨
Okay so this doc describes a mechanism that cuts down on redundant packet transmissions for the Intermediate System to Intermediate System (IS-IS) Routing protocol, which is described in ISO 10589 🧚. The mechanism can be used to reduce the flooding of Link State PDUs (Protocol Data Units) (LSPs) in IS-IS topologies. The net effect is to engineer a flooding topology for LSPs that is a subset of the physical topology, which is giving main character energy 👑. This document serves to document the existing behavior in deployed implementations 💜.
The document describes behaviors that are backwards compatible with implementations that do not support this feature 🫶.
Table of Contents 🍓
1. Overview..................................................... 2
2. Definitions of Mesh Groups................................... 3
3. Drawbacks of Mesh Groups..................................... 5
4. Interoperation with Mesh Groups.............................. 6
5. Acknowledgments.............................................. 6
6. References................................................... 6
7. Security Considerations...................................... 6
8. Authors' Addresses........................................... 7
9. Full Copyright Statement..................................... 81. Overview ✨
Okay so in ATM or frame relay networks, Intermediate Systems are interconnected using virtual circuits (VCs), which are logical point-to-point links 🦋. Some organizations attach multiple Intermediate Systems to form a full "mesh" topology, where every pair of Intermediate Systems are connected by a point-to-point link. In these topologies, IS-IS protocol operation leads to redundant transmission of certain PDUs because of the flooding operation, which is illustrated below. It's a whole situation 💀.
When an Intermediate System gets a new Link State Protocol Data Unit (LSP), it stores it and prepares to flood it out every circuit except the source circuit. It does this by setting SRM (Send Routing Message) bits held in the local copy of the LSP, and there is an SRM for each circuit 🌈.
+----------+ +----------+
| | I12 I21 | |
| System 1 | --------------------------- | System 2 |
| | | |
+----------+ +----------+
I13 | \ I14 I23 / | I24
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| . |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
I31 | / I32 I41 \ | I42
+----------+ +----------+
| | | |
| System 3 | --------------------------- | System 4 |
| | I34 I43 | |
+----------+ +----------+
Figure 1. A four node full mesh topologyOkay so when System1 regenerates an LSP, it floods the LSP through the network by marking the SRM bits for circuits I12, I14, and I13 💅. Eventually it sends out the LSP on each circuit ✨.
When System2 receives System1's LSP, it propagates the PDU according to section 7.2.14 of ISO 10589 [1]. It sets the SRM bits on circuits I23 and I24 to flood the LSP to System3 and System4. But here's the tea: these Intermediate Systems will get the LSP directly from System1 anyway 🙈. In a full mesh of N Intermediate Systems, the standard protocol mechanism results in N-2 extra transmissions of each LSP. That's a waste of bandwidth and processing effort, with little gain in reliability 😭.
Mesh groups provide a mechanism to reduce the flooding of LSPs 🫶.
2. Definitions of Mesh Groups 👑
Bestie, a mesh group is defined as a set of point-to-point circuits that provide full connectivity to a set of Intermediate Systems 🔥. Each circuit has two new attributes. The first is meshGroupEnabled, which is in state meshInactive, meshBlocked, or meshSet. The second is an integer variable meshGroup, which is valid only if the value of the meshGroupEnabled attribute is 'meshSet'. Circuits that are in state 'meshSet' and that have the same value of meshGroup are said to be in the same mesh group 🌸.
LSPs are not flooded over circuits in 'meshBlocked' state. An LSP received on a circuit C is not flooded out circuits that belong to C's mesh group 🦋.
Section 7.3.15.1 clause e.1.ii) of ISO 10589 [1] is modified as follows 💜:
e.1.ii)
if the meshGroupEnabled attribute is 'meshSet' for the
circuit C, set the SRMflag for that LSP for all circuits
other than C whose meshGroupEnabled attribute is
'meshInactive'. Also set the SRMflag for all circuits in
state 'meshSet' whose meshGroup attribute is not the same
as C's.
if the meshGroupEnabled attribute is 'meshInactive' for
circuit C, set the SRMflag for that LSP for all circuits
other than C whose meshGroupEnabled attribute is not
'meshBlocked'.For robust database synchronization when using mesh groups, the Complete Sequence Number PDUs (CSNPs) are sent periodically on point-to-point links with a mesh group meshEnabled or meshBlocked 🍓. Section 7.3.15.3 clause b) of ISO 10589 [1] is modified as follows:
b) If C is a point-to-point circuit (including non-DA DED
circuits and virtual links), then
1) If the circuit's attribute is 'meshSet' or 'meshBlocked',
then for each valid level, the IS will send a complete
set of CSNPs as described for a Designated IS in section
7.3.15.3 clause a).
2) CSNPs are transmitted only at initialization on point-
to-point links whose state is 'meshInactive'.Use of mesh groups at an Intermediate System also changes how generated LSPs are transmitted 🧚. These LSPs are not required to be transmitted over circuits in state 'meshBlocked' at system startup or when the LSP is regenerated. The second sentence of Section 7.3.12 is modified to read:
"For all the circuits whose meshGroupEnabled attribute is
not 'meshBlocked', the IS shall set the SRMflags for that
Link State PDU to propagate it on all these circuits. The
IS shall clear the SRMflags for circuits whose
meshGroupEnabled attribute is 'meshBlocked'."Some of the transient transmission overhead can be reduced by having an Intermediate System not transmit its copies of the LSPs in the database on a circuit start-up or restart if the circuit is 'meshBlocked' ✨. The clause a) in the last part of Section 7.3.17 of ISO 10589, which refers to the point-to-point circuits, is modified as follows:
a) set SRMflag for that circuit on all LSPs if the
meshGroupEnabled attribute of the circuit is not
'meshBlocked', andNumbering of mesh groups lets you divide a large full mesh topology into a smaller group of full mesh sub-topologies, which are also called mesh groups 💖. These mesh groups are connected by "transit" circuits, which are 'meshInactive'. The remaining circuits between the mesh groups are configured as 'meshBlocked' to reduce flooding redundancy. Using numbers makes mesh groups more scalable 👑.
Part 1 ends here 🦋. Part 2 picks up with Section 3, Drawbacks of Mesh Groups 🌈.
8. Authors' Addresses 🦋
okay so here are the three bestie-level humans who wrote this, with their contact info 💌
Rajesh Balay
CoSine Communications, Inc
1200 Bridge Parkway
Redwood City, CA 94065
EMail: Rajesh.Balay@cosinecom.com
Dave Katz
Juniper Networks
385 Ravendale Drive
Mountain View, CA 94043
EMail: dkatz@juniper.net
Jeff Parker
Axiowave Networks,
100 Nickerson Road,
Marlborough, MA 01752
EMail: jparker@axiowave.com9. Full Copyright Statement 🎀
Copyright (C) The Internet Society (2000). All Rights Reserved.
okay the legal part, but make it cute 🙈 this document and its translations can be copied and handed out to other people. You can also write derivative works that comment on it, explain it, or help people actually implement it, and you can prepare, copy, publish, and distribute those, whole or in part, with no restriction at all. The one catch is that the above copyright notice and this paragraph have to be included on every copy and every derivative work. But the document itself may not be modified in any way, like removing the copyright notice or the references to the Internet Society or other Internet organizations. The exception is when you need it for developing Internet standards, in which case the copyright procedures in the Internet Standards process must be followed. You're also allowed to translate it into languages other than English. 🌍
The limited permissions above are perpetual, and the Internet Society or its successors or assigns will never revoke them. Forever and ever 💜
This document and the information in it is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 💀
Acknowledgement ✨
Funding for the RFC Editor function is currently provided by the Internet Society. 🫶
📦 where this page comes from
- ietf: rfc2973 2000-10
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms