Hi Huaimo, Thank you for your proposal.
The area leader sub-tlv is only advertised by systems that are willing to be area leader. Presumably, that’s not necessarily all of the ones who support dynamic flooding. Thus, what you’re proposing moves one byte from one TLV into another TLV that will be more commonly used. So your proposal actually consumes more LSP space. The intention here is that the candidates for area leader advertise the Area Leader Sub-TLV. All nodes that support dynamic flooding would advertise the Dynamic Flooding Sub-TLV. Since the priority is part of the Area Leader election, it makes sense for it to be part of the Area Leader Sub-TLV. Regards, Tony p.s. IS-IS does not depend on word-alignment, so we typically do not leave reserved bytes in our TLV formats. OSPF is a different kettle of fish… :-) > On May 24, 2019, at 1:44 PM, Huaimo Chen <[email protected]> wrote: > > Hi Tony, > > An enhancement related to Area Leader Sub-TLV is briefed below for > discussions. A .pdf file is attached in the case that the formats below are > messed up. > > The leader of an area advertises an Area Leader Sub-TLV to indicate/instruct > whether centralized or distributed mode is to be used by all the nodes in the > area (Algorithm = 0: centralized mode; Algorithm = N (N>0): distributed mode > and N is the algorithm to be used by every node to compute flooding topology). > > Currently for IS-IS, IS-IS Area Leader Sub-TLV below is used by each of the > nodes to advertise its priority for becoming the leader > 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 | Priority | Algorithm | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Current) IS-IS Area Leader Sub-TLV > > It seems hard to understand that every node uses an Area Leader Sub-TLV to > advertise its priority for becoming the leader, and at the same time to > indicate/instruct whether centralized or distributed mode is to be used by > all the nodes in the area. > > When every node advertises an Area Leader Sub-TLV, only one for > indication/instruction for flooding reduction mode is used, and all the > others are not used, which consume space and processing time. > > An enhancement is to let every node advertise its priority for becoming the > leader and the algorithms that it supports though using a Dynamic Flooding > Sub-TLV, and only the leader advertise the indication for the flooding > reduction mode. To achieve this, some changes to the two Sub-TLVs and the > texts related to the Sub-TLVs should be made. > > For IS-IS, IS-IS Area Leader Sub-TLV is updated as follows (Priority is > removed) > 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 | Reserved | Algorithm | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Updated) IS-IS Area > Leader Sub-TLV > > The Priority is added into IS-IS Dynamic Flooding Sub-TLV. The current IS-IS > Dynamic Flooding Sub-TLV > 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 | Algorithm... | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Current) IS-IS Dynamic Flooding Sub-TLV > > is changed to: > 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 | Priority |Algorithm... | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Updated) IS-IS Dynamic Flooding Sub-TLV > > Similarly for OSPF, the current OSPF Area Leader Sub-TLV below > 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 | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > | Priority | Algorithm | Reserved | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Current) OSPF Area Leader > Sub-TLV > is changed to > 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 | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > | Reserved | Algorithm | Reserved | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Updated) OSPF Area Leader > Sub-TLV > > The current OSPF Dynamic Flooding Sub-TLV below > 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 | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > | Algorithm ... | | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Current) OSPF Dynamic Flooding Sub-TLV > is changed to > 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 | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > | Priority | Algorithm ... | | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > (Updated) OSPF Dynamic Flooding Sub-TLV > > > Best Regards, > Huaimo > > <EnhanceOnAdvertisePriority4Leader.pdf>
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