From: Pascal Hambourg <pascal.mail@plouf.fr.eu.org>
To: ratheesh k <ratheesh.ksz@gmail.com>
Cc: netfilter@vger.kernel.org
Subject: Re: symmetric NAT and ICMP
Date: Wed, 05 May 2010 13:29:39 +0200 [thread overview]
Message-ID: <4BE156A3.2010204@plouf.fr.eu.org> (raw)
In-Reply-To: <AANLkTinm_rvGHEZQ_RpBqfvERQgI1JXNlBjn00owut6o@mail.gmail.com>
Hello,
ratheesh k a écrit :
>
> My understanding is : - NAT on Router R is symmetric nat . I am able
> to browse internet from both machine A and B .
>
> My question is : Can Router R can support different types of NAT
> simultaneously ( full cone nat ,address restricted nat ....etc ) ?
I don't think so. NAT behaviour is determined by how the connection
tracking works.
> IF only one type of nat is supported , how "ping google.com " works
> from both machine ? icmp dont have any port information .Still
> icmp-reply gets routed to correct machine ?
ICMP request/reply types (echo, timestamp...) contain an identifier
field that helps matching requests and replies (Cf. RFC 792). Conntrack
uses it, see /proc/net/ip_conntrack or /proc/net/nf_conntrack, e.g. :
icmp 1 27 src=192.168.0.1 dst=192.168.0.2 type=8 code=0 id=62027
[UNREPLIED] src=192.168.0.2 dst=192.168.0.1 type=0 code=0 id=62027 use=2
mark=0
icmp 1 14 src=192.168.0.1 dst=192.168.0.2 type=8 code=0 id=61259
[UNREPLIED] src=192.168.0.2 dst=192.168.0.1 type=0 code=0 id=61259 use=1
mark=0
Two different pings with the same source and destination but different
identifiers create two separate conntrack entries.
next prev parent reply other threads:[~2010-05-05 11:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-05 10:29 symmetric NAT and ICMP ratheesh k
2010-05-05 10:38 ` ratheesh k
2010-05-05 11:29 ` Pascal Hambourg [this message]
2010-05-05 11:41 ` ratheesh k
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