Inline: GV> From: Tony Li <tony1ath...@gmail.com> On Behalf Of Tony Li Sent: Wednesday, August 24, 2022 5:26 PM To: Van De Velde, Gunter (Nokia - BE/Antwerp) <gunter.van_de_ve...@nokia.com> Cc: lsr <lsr@ietf.org> Subject: Re: [Lsr] New Version Notification for draft-pkaneria-lsr-multi-tlv-01.txt
Hi Gunter, I am having troubles understanding the value of ‘The Multi-part TLV Capability’ flag. What would break if ‘Multi-part TLV Capability’ flag would not exist? A system that supported MP-TLVs would not be able to determine that there were other systems in the area that did not support MP-TLVs. The system might then advertise MP-TLVs and they would be misinterpreted or cause system crashes in the systems that did not support them. GV> crashes? I really hope that is not happening. GV> When a legacy router receives MP-TLVs from another system and legacy router has no support for handling MP-TLV, then yes, things get misinterpreted. There is nothing wrong with that, is there? Do you have an example where things go wrong? If we want to introduce MP-TLVs, that change would warrant the existence of the flag. GV> I am not convinced yet how a MP-TLV catch-all flag would make ISIS behave better I dispute that a binary flag warrants the word ‘complexity’. GV> living without binary flag is simpler and less complex then dealing with a binary flag. (i.e. what, when, how, why, who sets this flag?) Note: thoughts about the flag: What if a system by accident sends flip-flopping (set/unset/set/unset/etc) of this flag? Then other systems might misinterpret the results and generate inconsistent TLVs. That would be bad. GV> correct, no good at all. What if an advertising system support multi-tlv for TLV ‘A’ but not for TLV ‘B’? We are not allowing that level of granularity. A system that is going to support MP-TLVs should take care to operate correctly for ALL TLVs before advertising that it supports them. GV> I suspect that 'ALL TLVs' is a reference to ALL TLVs supported by the local system. This means that e.g. when new TLVs would be supported after a system upgrade, that the operator has to be aware and correct the flag during each single upgrade. GV> Unfortunately I remain to have troubles understanding the value "Multi-part TLV Capability’ flag brings to an ISIS network. * Without flag it is indeed uncertain if area wide mp-tlv is supported (sub-optimal). * but with catch all MP-TLV flag I am not sure we improve ISIS operation: ** Who guarantees that the flag is set correctly on all systems at all times ** Maybe all systems falls back to advertise single TLV because another (legacy?) system advertise a wrong flag (sub-optimal) ** Legacy system with MP-TLV support gets upgraded and now supports additional TLVs but not with MP-TLV... ?manual intervention? (sub-optimal) ** what, when, how, why, who sets the MP-TLV flag? What with flapping of MP-TLV flag (undefined) G/ Tony _______________________________________________ Lsr mailing list Lsr@ietf.org https://www.ietf.org/mailman/listinfo/lsr
