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Policy Statements



"Jumbo" Frames and Internet2

Large IP frames, also called "jumbograms" or "jumboframes," have been recommended for high-performance networkslike Internet2 as a significant factor in increasing performance overlong distances. In general the limiting factor in frame size is theIP MTU (Media Transmission Unit, sometimes also called MaximumTransmission Unit), which by default on an Ethernet is 1500 bytes.The MTU is set independently for every interface in an IP flow'spath, and any interface can limit the size of the flow by fragmentingit. Path MTU discovery, described in RFC1191,attempts to discover the optimal MTU for the path to avoid fragmentation.

The Internet2 recommendation is to work toward an end-to-end IP MTU ofat least 9000 bytes today, and eventually much larger. Steps in thiseffort are:

  1. Set 9KB MTUs throughout the Internet2 backbone. This has been completed.
  2. Internet2 and its connectors work together to set 9KB MTUs where we peer with each other. See the table below for an indication of the progress of this effort.
  3. The Internet2 institutions set 9KB MTUs within their networks, at least to the high-performance end-stations.
    This page gives links to some of the reasoning for a large-frame recommendation, indicates some of the organizations and networks who have endorsed the concept and are working with us to increase MTUs, shows how it is done with Cisco and Juniper examples, and finally includes a list of all Internet2 connectors and peer networks and their current MTU status.

this page is locate at http://noc.net.internet2.edu/i2network/documentation/policy-statements/rrsum-almes-mtu.html
it was last edited on 1 April2003
comments to Brent Sweeny,sweeny@indiana.edu

Internet2 Prefix-Length Policy

The following was sent to the Internet2 operations list on 17 January 2003.


Internet2 encourages its connectors to aggregate advertised prefixes as an internet best practice. Therefore, we will accept approved IPv4 prefixes up through /27. However, we realize that in unusual special cases, prefixes more specific than /27 must be advertised, so if there is an important reason a prefix more specific than /27 must be advertised, explain your need and we will try to accomodate you.

Since connectors are the only ones from whom specific prefixes are accepted, this policy applies so far only to Internet2 connectors (i.e. not to peer networks).


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