+1 Thanks, Chris.
> On Apr 2, 2019, at 13:25, [email protected] wrote: > > > I am in complete agreement with both Les’s extensive analysis and opinion. > ;-) > > Tony > > >> On Apr 2, 2019, at 8:37 AM, Les Ginsberg (ginsberg) <[email protected]> >> wrote: >> >> In reply to my own post, here is my opinion regarding including LANs in the >> Flooding Topology: >> >> While I think it would be "nice" and simplifying to be able to ignore LANs, >> I think we are unable to do so because the possibility that LANs are >> actually in use as transit links in some topologies exists. >> >> NOTE: I am not persuaded by the argument that some operators have LANs that >> could be operated in point-to-point mode but they simply don't configure the >> links to do so. If a customer is serious about flooding reduction then they >> need to also do what they can to reduce unnecessary LSPs/LSAs from even >> being generated. >> >> Even if we treat LANs as always enabled for flooding , any algorithm to >> calculate the flooding topology would be sub-optimal if it did not consider >> the fact that flooding is occurring on the LANs. >> >> Bottom line, unless we are confident that LANs will not exist in the >> topologies where flooding optimizations will be used, not supporting LANs >> seems to be an undesirable restriction. >> >> Les >> >> >>> -----Original Message----- >>> From: Lsr <[email protected]> On Behalf Of Les Ginsberg (ginsberg) >>> Sent: Tuesday, April 02, 2019 8:31 AM >>> To: [email protected]; [email protected] >>> Subject: [Lsr] Open issues with Dynamic Flooding: Including LANs in the >>> Flooding Topology >>> >>> (I have altered the subject so we can discuss the two issues in Tony's >>> previous post separately.) >>> >>> >>> There are several aspects to consider when discussing LAN support in the >>> context of flooding optimizations: >>> >>> 1)Flooding topology advertisement (centralized mode only) >>> >>> Support for encoding LANs when advertising the flooding topology requires >>> that >>> we include not only all routers in the set of "nodes" in the network but >>> also >>> (to use IS-IS terminology) all “pseudo-nodes” as well. This means when >>> advertising the set of nodes and associated indeces used in calculating the >>> flooding topology there needs to be an indication as to whether a given >>> entry is a node or a pseudo-node. The encoding for this is straightforward >>> in IS-IS (include pseudo-node ID in the node identifier) but more complex >>> in OSPF. >>> >>> However, this is a problem with a straightforward solution and is therefore >>> not a significant consideration. >>> >>> 2)Enablement/disablement of flooding on a LAN >>> >>> Correct operation of flooding on a LAN requires all nodes connected to the >>> LAN perform their role when the LAN is enabled for flooding and conversely >>> all nodes suppress flooding via the LAN when flooding is disabled for >>> flooding. This applies to temporary enablement of flooding on a LAN in the >>> event of a partitioned flooding topology i.e., if any node connected to the >>> LAN >>> signals enablement of temporary flooding on the LAN all nodes connected to >>> the >>> LAN MUST honor that request. >>> >>> Selective enablement of flooding on a LAN based on whether it is part >>> of the calculated flooding topology therefore entails some additional >>> complexity. >>> >>> Note that this discussion assumes that flooding operation on a LAN >>> is not altered by the introduction of flooding optimizations. For example >>> there is no proposal to selectively enable transmission of LSPs/LSAs on >>> a LAN only by a subset of the nodes connected to the LAN. >>> >>> 3)Use of LANs in flooding topology algorithms >>> >>> When LANs are considered part of the flooding topology, any algorithm >>> used to compute the flooding topology has to consider how to use LANs. >>> For example, using a LAN might have an advantage in that by enabling >>> flooding on a single LAN multiple nodes are now connected to the flooding >>> topology. This might reduce the number of point-to-point edges required >>> in the flooding topology and/or decrease the diameter of the flooding >>> topology. >>> >>> But use of a LAN might either increase the diameter of the flooding topology >>> and thereby affect convergence or unnecessarily increase the degree of >>> connectivity of certain nodes to the flooding topology and thereby reduce >>> the optimization achieved. >>> >>> If LANs are always enabled for flooding but are not included in the set of >>> nodes considered as part of the flooding topology (see point #1 above) then >>> "false partitions" might occur during the calculation of the flooding >>> topology. >>> >>> Whether LANs are considered part of the flooding topology or not, the >>> presence >>> of a LAN introduces the possibility that there are "hidden nodes" to which >>> flooding is actually occurring but which are not explicitly mentioned in >>> the calculated flooding topology. >>> >>> 4)Deployment Limitations >>> >>> The significance of support for LANs depends upon their existence in a >>> deployment where the use of flooding optimizations is desired. >>> >>> If all links are point-to-point then the question is irrelevant. >>> >>> If all links are point-to-point but ethernet links have not been configured >>> to operate in point-to-point mode then lack of support for LANs would >>> compromise the value of flooding optimizations. A counter argument to this >>> case is that unnecessary operation in LAN mode itself increases the number >>> of >>> LSPs/LSAs that need to be flooded by as much as 50% and therefore is >>> something which SHOULD be addressed by altering configuration. There >>> should >>> then be motivation for network operators to enable point-to-point operation >>> where possible even if they have not done so before. >>> >>> If LANs with more than 2 connected nodes are present and are used for >>> transiting traffic then lack of support for LAN circuits for flooding >>> optimizations will lead to diminished effectiveness of flooding >>> optimizations. >>> >>> Summary: >>> >>> When forming an opinion on whether to include LANs in the flooding >>> topology >>> it is prudent to consider the above points. >>> >>> >>> >>> _______________________________________________ >>> Lsr mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/lsr > > _______________________________________________ > Lsr mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lsr _______________________________________________ Lsr mailing list [email protected] https://www.ietf.org/mailman/listinfo/lsr
