On 16.01.2020 19:07, Victor Sudakov wrote: > Eugene Grosbein wrote: >> >>> What beats me is that I cannot reproduce this problem in bhyve. In this >>> packet dump: http://admin.sibptus.ru/~vas/ipsec1.pcap.gz I'm scp-ing a >>> 50M file from 192.168.246.10 (bhyve guest) to 192.168.246.1 (bhyve >>> host), and I see no fragments, and the largets packet is 1466 bytes, and >>> the scp never stalls nor fails. >>> >>> Why is it NOT broken this time? >>> >>> Both hosts are 12.1-RELEASE-p1. >> >> I could not reproduce the problem with unpatched recent stable/11, either :-) > > Is there a way to view the MSS in the TCP segments before encryption or > after decryption? I want to compare them in situations with IPSec > enabled and disabled. > > I've never been able to see anything in "tcpdump -i enc0", probably it > cannot do transport mode IPSec because the man page talks about "outer > and inner header."
For transport mode inner and outer headers will be the same.
I guess the problem can be reproduced in the lab using the following config:
[Host A] <--> [Router] <--> [Host B]
IPsec should be configured between hosts A and B. Then you need to
reduce MTU on the router. This should lead to ICMP NEEDFRAG messages
from the router, and then host should correctly handle them.
--
WBR, Andrey V. Elsukov
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