[dns-operations] DNS flag day 2020: Recommended EDNS buffer size discussion
ler762 at gmail.com
Mon Sep 2 20:41:55 UTC 2019
On 9/2/19, Paul Vixie <paul at redbarn.org> wrote:
> On Monday, 2 September 2019 17:31:50 UTC Lee wrote:
>> On 9/2/19, Paul Vixie <paul at redbarn.org> wrote:
>> > ...
>> >> we should not needlessly invent something that's different from TCP
>> >> MSS.
>> >> just use what works.
>> I think tcp mss working as well as it does is because the mss is
>> negotiated at connection setup time (syn, syn+ack option tcp mss
Are we arguing definitions?
Source sends a SYN with the tcp mss option set to 1460, destination
responds with a SYN+ACK with the tcp mss option set to 1280, both
sides use an mss of 1280. Which sounds like a negotiation to me..
>> Your machine can figure out the mss & middle boxes that know
>> better can reduce the mss value to something they know will work.
>> eg. 'ip tcp adjust-mss ' in ciscoland
>> How do you do that with udp?
> TCP MSS is an offer not an acknowledgement,
> and it proceeds from local
> knowledge of the path MTU like the routing table or the sysctl definitions
> by a sysadmin. generally speaking path MTU discovery does not work
Right - generally speaking path MTU discovery does not work. So when
setting up ipsec tunnels between routers I'd also configure ip tcp
adjust-mss to lower the offered mss on traffic going through the
tunnel & have everything work.
I never did figure out how to automatically fix udp traffic. So I'm
not understanding how your suggestion to use what works for tcp is
applicable to udp.
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