From: "William N." <netfilter@riseup.net>
To: netfilter@vger.kernel.org
Subject: Correct way of setting the TCP max segment sizes for IPv4 and IPv6?
Date: Mon, 8 Apr 2024 19:24:41 -0000 [thread overview]
Message-ID: <20240408192441.657ac116@localhost> (raw)
Hi,
I have been looking at some firewall hardening examples which suggest
setting the TCP maximum segment sizes but they do it only for IPv4.
Looking at RFC 9293, §3.7.1, I see those MSS values are different for
IPv6, so I am approaching this like this:
chain ingress {
type filter hook ingress device "eth0" priority -500; policy accept;
# ...
# IPv4
meta protocol ip tcp flags syn tcp option maxseg size < 536 drop
# IPv6
meta protocol ip6 tcp flags syn tcp option maxseg size < 1220 drop
}
My questions:
1. Is this the correct way to do this?
2. Is it good to do this (setting TCP MSS) at all?
3. Which is better and why:
meta protocol ip tcp flags syn tcp option maxseg size < 536 drop
or
meta protocol ip tcp flags syn tcp option maxseg size 1-535 drop
4. How do I test if this works correctly? (Debian 12 here)
next reply other threads:[~2024-04-08 19:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-08 19:24 William N. [this message]
2024-04-09 18:43 ` Correct way of setting the TCP max segment sizes for IPv4 and IPv6? Slavko
2024-04-09 19:33 ` William N.
2024-04-09 22:04 ` Slavko
2024-04-10 15:48 ` William N.
2024-04-10 18:02 ` Slavko
2024-04-10 18:24 ` William N.
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