[c-nsp] ip tcp adjust-mss

[Tony]

http://en.wikipedia.org/wiki/Path_MTU_Discovery





________________________________
 From: Methsri Wickramarathna <mmethw2003 at gmail.com>
To: cnsp at marenda.net 
Cc: "cisco-nsp at puck.nether.net" <cisco-nsp at puck.nether.net> 
Sent: Tuesday, 5 November 2013 10:59 AM
Subject: Re: [c-nsp] ip tcp adjust-mss
 

Thanks Tony , John and Juergan...

This has been issue for many sites mainly towards 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> 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] Im Auftrag
> > von Methsri Wickramarathna
> > Gesendet: lundi 4 novembre 2013 17:55
> > An: Pete Lumbis
> > Cc: 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
> > mturoute to 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
> [...]
>
>


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~~( ŊëŌ )~~

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