[c-nsp] ip tcp adjust-mss
Octavio Alvarez
alvarezp at alvarezp.ods.org
Tue Nov 5 11:15:48 EST 2013
It's not *necessarily* a buggy device. I meant to explain why could the
problem be anywhere.
That said, if negotiation is being kept at 1460, you possibly have a
link (like DSLs do) that has a lower MTU but the router doesn't know.
Just follow Juergen's advice: set MSS to conservative values on a far
end and see if it helps. Then play with the value to see how high you
can go.
On 11/04/2013 09:54 PM, Methsri Wickramarathna wrote:
> I have captured and analyzed the packets from wireshark and it shows MSS
> agreement is set to 1460. Is there any convenient way to track the buggy
> device ???
>
>
> On Tue, Nov 5, 2013 at 10:39 AM, Octavio Alvarez
> <alvarezp at alvarezp.ods.org <mailto:alvarezp at alvarezp.ods.org>> wrote:
>
> It could be anywhere.
>
> I remember seeing buggy devices that didn't dynamically adapt to
> intermediate TCP MSS modifications. We had to analyze the TCP headers on
> the streams to find this out. It was a reflected symptom.
>
> I've also seen it on DSL links that didn't had "ip tcp adjust-mss 1452"
> in place.
>
>
>
> On 11/04/2013 08:09 PM, Methsri Wickramarathna wrote:
> > Thanks Blake & Tony,
> >
> > Is this issue with My end core router , destination end device or
> > intermediate device ???
> >
> > Is there any way I can find this ???
> >
> >
> >
> > On Tue, Nov 5, 2013 at 7:22 AM, Blake Dunlap <ikiris at gmail.com
> <mailto:ikiris at gmail.com>> wrote:
> >
> >> Yes. Don't do that.
> >>
> >>
> >> On Mon, Nov 4, 2013 at 6:59 PM, Methsri Wickramarathna <
> >> mmethw2003 at gmail.com <mailto:mmethw2003 at gmail.com>> wrote:
> >>
> >>> Thanks Tony , John and Juergan...
> >>>
> >>> This has been issue for many sites mainly towards yahoo.com
> <http://yahoo.com>. Can any one
> >>> explain why this is happening for particular IPs in a subnet ???
> >>> We are using access list inbound & Outbound to prevent ICMPs cumming
> >>> inside
> >>> to our network, will it be creating this problem ????
> >>>
> >>>
> >>> On Tue, Nov 5, 2013 at 3:23 AM, <cnsp at marenda.net
> <mailto:cnsp at marenda.net>> wrote:
> >>>
> >>>> Hi, this looks like a CPE-device
> >>>> With static IP-adresses and routing.
> >>>>
> >>>> You may really want to set "ip tcp adjust-mss 1280"
> >>>> on _both_ your WAN and your (probably natted) LAN (L3) Interfaces.
> >>>> (_both_ sides, yes !)
> >>>>
> >>>> This will help you in most cases with
> >>>> MTU restrictions on
> >>>> - your link
> >>>> - home-"web"servers behind Broadband links
> >>>> etc.
> >>>>
> >>>> Yes, the value is not optimized but very computerish ( 2**10 +
> 2**8 ),
> >>>> but it is good for
> >>>> - pppoe (1500-8=1492)
> >>>> - l2tp forwarded dial-in sessions (l2tp overhead+pppoe leads to
> 1456)
> >>>> - even with an additional vlan tag ( so MTU will be 1452 found
> in most
> >>>> literature)
> >>>> - some other tunneled environments
> >>>>
> >>>> Iff you are an ISP,
> >>>> you will configure this _only_ on the virtual-template interfaces
> >>>> on your LNSes for broadband-termination .
> >>>>
> >>>> Keep it out of your core,
> >>>> You will not want to modify your valued customer's ip packets
> >>>> in your core network; here you want to use a MTU greater than 1500
> >>>> while on your BGP up/downstreams will stay at Ethernet-default
> 1500 .
> >>>>
> >>>> Sorry, very conservative, but will avoid may problems.
> >>>>
> >>>> Just my 0.01 $ on this
> >>>>
> >>>> Juergen.
> >>>>
> >>>>> -----Ursprüngliche Nachricht-----
> >>>>> Von: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net
> <mailto:cisco-nsp-bounces at puck.nether.net>] Im Auftrag
> >>>>> von Methsri Wickramarathna
> >>>>> Gesendet: lundi 4 novembre 2013 17:55
> >>>>> An: Pete Lumbis
> >>>>> Cc: cisco-nsp at puck.nether.net <mailto:cisco-nsp at puck.nether.net>
> >>>>> Betreff: Re: [c-nsp] ip tcp adjust-mss
> >>>>>
> >>>>> Thanks Pete,
> >>>>>
> >>>>> If not a problem can any one look in to following mturoute
> taken ???
> >>> :)
> >>>>>
> >>>>> E:\>mturoute -t www.ubnt.com <http://www.ubnt.com>
> >>>>> mturoute to www.ubnt.com <http://www.ubnt.com>, 30 hops max,
> variable sized packets
> >>>>> * ICMP Fragmentation is not permitted. *
> >>>>> * Speed optimization is enabled. *
> >>>>> * Maximum payload is 10000 bytes. *
> >>>>> 1 +- host: 116.12.78.1 max: 1500 bytes
> >>>> [...]
> >>>>
> >>>>
> >>>
> >>>
> >>> --
> >>> --
> >>> ________´$$$$`_____________________________,,,_
> >>> _______´$$$$$$$`_________________________´$$$`
> >>> ________`$$$$$$$`______,,________,,_______´$$$$´
> >>> _________`$$$$$$$`____´$$`_____´$$`____´$$$$$´
> >>> __________`$$$$$$$`_´$$$$$`_´$$$$$`__´$$$$$$$´
> >>> ___________`$$$$$$$_$$$$$$$_$$$$$$$_´$$$$$$$´_
> >>> ____________`$$$$$$_$$$$$$$_$$$$$$$`´$$$$$$´_
> >>> ___,,,,,,______`$$$$$$_$$$$$$$_$$$$$$$_$$$$$$´_
> >>> _´$$$$$`____`$$$$$$_$$$$$$$_$$$$$$$_$$$$$$´_
> >>> ´$$$$$$$$$`´$$$$$$$_$$$$$$$_$$$$$$$_$$$$$´_
> >>> ´$$$$$$$$$$$$$$$$$$_$$$$$$$_$$$$$$$_$$$$$´_
> >>> ___`$$$$$$$$$$$$$$$_$$$$$$$_$$$$$$_$$$$$$´_
> >>> ______`$$$$$$$$$$$$$_$$$$$__$$_$$$$$$_$$´_
> >>> _______`$$$$$$$$$$$$,___,$$$$,_____,$$$$$´_
> >>> _________`$$$$$$$$$$$$$$$$$$$$$$$$$$$$$´_
> >>> __________`$$$$$$$$$$$$$$$$$$$$$$$$$$$´_
> >>> ____________`$$$$$$$$$$$$$$$$$$$$$$$$´_
> >>> _______________`$$$$$$$$$$$$$$$$$$$$´_
> >>>
> >>> ~~( ŊëŌ )~~
> >>> _______________________________________________
> >>> cisco-nsp mailing list cisco-nsp at puck.nether.net
> <mailto:cisco-nsp at puck.nether.net>
> >>> https://puck.nether.net/mailman/listinfo/cisco-nsp
> >>> archive at http://puck.nether.net/pipermail/cisco-nsp/
> >>>
> >>
> >>
> >
> >
>
>
>
>
> --
> --
> ________´$$$$`_____________________________,,,_
> _______´$$$$$$$`_________________________´$$$`
> ________`$$$$$$$`______,,________,,_______´$$$$´
> _________`$$$$$$$`____´$$`_____´$$`____´$$$$$´
> __________`$$$$$$$`_´$$$$$`_´$$$$$`__´$$$$$$$´
> ___________`$$$$$$$_$$$$$$$_$$$$$$$_´$$$$$$$´_
> ____________`$$$$$$_$$$$$$$_$$$$$$$`´$$$$$$´_
> ___,,,,,,______`$$$$$$_$$$$$$$_$$$$$$$_$$$$$$´_
> _´$$$$$`____`$$$$$$_$$$$$$$_$$$$$$$_$$$$$$´_
> ´$$$$$$$$$`´$$$$$$$_$$$$$$$_$$$$$$$_$$$$$´_
> ´$$$$$$$$$$$$$$$$$$_$$$$$$$_$$$$$$$_$$$$$´_
> ___`$$$$$$$$$$$$$$$_$$$$$$$_$$$$$$_$$$$$$´_
> ______`$$$$$$$$$$$$$_$$$$$__$$_$$$$$$_$$´_
> _______`$$$$$$$$$$$$,___,$$$$,_____,$$$$$´_
> _________`$$$$$$$$$$$$$$$$$$$$$$$$$$$$$´_
> __________`$$$$$$$$$$$$$$$$$$$$$$$$$$$´_
> ____________`$$$$$$$$$$$$$$$$$$$$$$$$´_
> _______________`$$$$$$$$$$$$$$$$$$$$´_
>
> ~~( ŊëŌ )~~
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