From: Grant <emailgrant@gmail.com>
To: Gentoo mailing list <gentoo-user@lists.gentoo.org>
Subject: Re: [gentoo-user] PMTUD
Date: Sun, 1 Sep 2013 06:59:19 -0700 [thread overview]
Message-ID: <CAN0CFw1vuFeOBrLYWbrVG_gUaDwypMKa8rmiY0pUqoTDYR+3UA@mail.gmail.com> (raw)
In-Reply-To: <201309011357.12792.michaelkintzios@gmail.com>
>> Could ICMP packets not getting through be to blame for my proxy server
>> problem? My laptop can't seem to ping anyone (blocked at the firewall
>> in this hotel I suppose) and certainly the proxy server can't ping my
>> laptop.
>
> Not all ICMP packets are relevant to detecting the MTU of a node. A correctly
> implemented node will return an ICMP Fragmentation Needed (Type 3, Code 4)
> packet, with its MTU value. This kind of ICMP packets should not be blocked
> at firewalls. Use ping with the do not fragment option to see if packets
> above a certain size time out, i.e. they are dropped by some offending node on
> the way.
>
> ping -c 6 -n -M do -s 1472 <server_address>
I get "Frag needed and DF set (mtu = 1492)" when pinging google.com.
I get normal replies with -s 1464. ifconfig shows my WAN interface at
MTU 1500 so PMTUD must change the MTU for communication with
google.com if I understand correctly.
> Of course, if the hotel's firewall is blocking all outgoing/incoming pings
> this sort of diagnostic test will not be useful.
I actually only lose pings to my own remote system so I've started a
new thread about that. I tried down to -s 1 but still 100% packet
loss there.
- Grant
next prev parent reply other threads:[~2013-09-01 13:59 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-27 8:10 [gentoo-user] PMTUD Grant
2013-08-27 14:27 ` Mick
2013-09-01 7:40 ` Grant
2013-09-01 8:37 ` Mick
2013-09-01 10:31 ` Grant
2013-09-01 12:00 ` Mick
2013-09-01 12:09 ` Grant
2013-09-01 11:17 ` Grant
2013-09-01 12:57 ` Mick
2013-09-01 13:59 ` Grant [this message]
2013-09-01 15:43 ` Mick
2013-09-01 16:17 ` Grant
2013-09-01 16:53 ` Mick
2013-09-01 17:54 ` Grant
2013-09-01 18:51 ` Mick
2013-09-02 18:34 ` Grant
2013-09-02 22:29 ` Mick
2013-09-05 12:52 ` Grant
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