Re: MTU SIZE?

Отправлено: Михаил Кадер on September 08, 1997 at 20:37:29:

В ответ на: MTU SIZE? posted by Евгений Збаражский on August 28, 1997 at 14:31:29:

> какой MTU Size для модемо 28.000
> Cisco 2511 IOS 11.2
> Спасибо

Specify the MTU Size of IP Packets

The maximum transmission unit (MTU) refers to the size of an IP packet. You might want to change to a smaller MTU size for
any of the following reasons:

The SLIP or PPP application at the other end only supports packets up to a certain size.

You want to assure a shorter delay by using smaller packets.

The host Telnet echoing takes longer than 0.2 seconds.

For example, at 9600 baud a 1500 byte packet takes about 1.5 seconds to transmit. This delay would indicate that you
want an MTU size of about 200 (1.5 seconds / 0.2 seconds = 7.5 and 1500 byte packet/ 7.5 = 200 byte packet).

To specify maximum IP packet size, perform the following task in interface configuration mode:

Task
Command
Specify the size of the largest IP packet that the asynchronous
line can support.
ip mtu bytes

The MTU size can be negotiated by TCP, regardless of the asynchronous interface settings. In other words, TCP running on
the device to which the communication server is connected can negotiate for a different MTU size than is configured on the
communication server. The communication server performs IP fragmentation of packets larger than the specified MTU. Do not
change the MTU size unless the SLIP or PPP implementation running on the host at the other end of the asynchronous line
supports reassembly of IP fragments. Because each fragment occupies a spot in the output queue, it might also be necessary to
increase the size of the SLIP or PPP hold queue, if your MTU size is such that you might have a high amount of fragments of
packets in the output queue.

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