From: Oliver Boehmer (oboehmer@xxxxxxxxx)
Date: Thu May 30 2002 - 10:26:13 GMT-3
At 15:28 30.05.2002 +0900, Tom Young wrote:
>HI,
>
> I want to ask a question about MTU configuration. In
>Japan, we have a DSL internet access type named "B-Flez",
>if I use this type , the frame size couldn't exceed 1450,
>if I want to set this figure, just wirte
>"mtu 1450" in the DSL port is ok?
In theory this would be enough, practice shows that "Path MTU Discovery
(PMTUD)" does not always work, so there will be some problems when browsing
the Internet (some web sites work, others don't).
So you want to make sure that you also adjust your Ethernet's MTU (where
your host is connected) accordingly (on the router and all machines
connected to it). If you don't want to do this, you can also configure "ip
tcp adjust-mss 1450" on the outgoing interface, this way IOS will intercept
SYN packets exchanged during the initial TCP handshake and adjust the MSS
so remote servers will not send packets larger than 1450 bytes.
See also http://www.cisco.com/warp/public/105/56.html which describes a
related problem with GRE tunnels, but PPPoE has the same issues..
oli
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:59:12 GMT-3