From: Florian Westphal <fw@strlen.de>
To: Juan Carlos Lazcano <juan@placidnetworks.com>
Cc: "netfilter@vger.kernel.org" <netfilter@vger.kernel.org>
Subject: Re: Stateless NAT in nftables with maps for performance
Date: Fri, 12 Sep 2025 15:37:36 +0200 [thread overview]
Message-ID: <aMQiIC9016sR9Djw@strlen.de> (raw)
In-Reply-To: <1714012059.534025.1757681233048@email.ionos.com>
Juan Carlos Lazcano <juan@placidnetworks.com> wrote:
> My echo/reply base icmp functionality for v4 is working atleast at a cursory glance, without further testing I'm not sure what other parts of icmp are not working with this approach.
Internal addresses leak via icmp dst unreach, redirects etc. which contain copies of
the (rewritten or original) addresses.
That in turn breaks path mtu discovery for instance:
Server may see internal address reflected in embedded header.
Client can receive error for source address it doesn't have.
NAT engine also rewrites embedded headers, see e.g. nf_nat_ipv4_fn()
in net/netfilter/nf_nat_proto.c and nf_nat_icmp_reply_translation() to
avoid this.
next prev parent reply other threads:[~2025-09-12 13:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-12 11:28 Stateless NAT in nftables with maps for performance Juan Carlos Lazcano
2025-09-12 12:05 ` Florian Westphal
2025-09-12 12:23 ` Florian Westphal
2025-09-12 12:47 ` Juan Carlos Lazcano
2025-09-12 13:37 ` Florian Westphal [this message]
2025-09-15 9:11 ` Pablo Neira Ayuso
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