Re: [v6ops] Proxy function for PTB messages on the tunnel end

[Vasilenko Eduard <[e-mail]>]

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:[e-mail]]
Sent: Wednesday, March 24, 2021 11:50 PM
To: Vasilenko Eduard <[e-mail]>
Cc: [e-mail]; int-area <[e-mail]>
Subject: Re: Proxy function for PTB messages on the tunnel end

Eduard,


On Mar 24, 2021, at 1:04 PM, Vasilenko Eduard <[e-mail]<mailto:[e-mail]>> 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