Hi Joseph, It is exactly that I do not like most: complete eradicate PMTUD from any tunnel environment. Just prohibit it. RFC 2473: 6.7<https://tools.ietf.org/html/rfc2473#section-6.7> IPv6 Tunnel MTU The tunnel MTU is set dynamically to the Path MTU between the tunnel entry-point and the tunnel exit-point nodes, minus the size of the tunnel headers …
The tunnel entry-point node performs Path MTU discovery on the path between the tunnel entry-point and exit-point nodes Eduard From: Joseph Touch [mailto:[email protected]] Sent: Wednesday, March 24, 2021 11:50 PM To: Vasilenko Eduard <[email protected]> Cc: [email protected]; int-area <[email protected]> Subject: Re: Proxy function for PTB messages on the tunnel end Eduard, On Mar 24, 2021, at 1:04 PM, Vasilenko Eduard <[email protected]<mailto:[email protected]>> wrote: Hi Joseph, You have presented below (and in many other messages) a long list of policies (extensive usage of “SHOULD”, “NEVER”, “MUST”) That are new – would change how current tunnels operate Some do, yes. To make them consistent and correct. Why virtual link could not send ICMP PTB (like on a physical link)? Just because… it is “unsolicited”. But one moment – any other PTB is unsolicited too - It is an event. PTBs are only sent when a packet arrives at a router and the router decides to forward that packet to a link whose link MTU is too small. If the link MTU changes, there would never be an ICMP PTB *until* a new packet is sent. Go ahead - change the MTU of any interface (tunnel or not) of any router and tell me if you see a PTB being sent *ANYWHERE*. Nothing happens until the next packet goes to that interface. I.e., PTBs are always in response to an attempt to send a packet - not merely to an interface change. Joe
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