Mailinglist Archive: opensuse (1599 mails)

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Re: [opensuse] how many folks running suse 11 are heavily into IPv6?
  • From: James Knott <james.knott@xxxxxxxxxx>
  • Date: Sun, 18 Oct 2009 18:17:11 -0400
  • Message-id: <4ADB93E7.1020303@xxxxxxxxxx>
John E. Perry wrote:
Per Jessen wrote:

James Knott wrote:


Per Jessen wrote:

Adam Tauno Williams wrote:

]


* is faster for local transfers (gone are MTU/MRU & fragmentation
issues)


How does IPv6 do that - isn't MTU dependent on the ethernet packet
size and router support for the same?



When was the last time you saw anything that didn't support 1500 byte
MTU?

This morning :-)
I have an IPv4 setup which uses IPIP tunnels on the back of LVS, and
those tunnels reduce my MTU to 1440.

Still, how does IPv6 avoid MTU/MRU & fragmentation issues? PMTU is
surely still required.




...But isn't fragmentation a good thing? And isn't it good to be able to
specify how much fragmentation to allow? How, otherwise, does one avoid
a 50MB file transfer, for instance, locking up a 54Mbps wifi network for
10 seconds? Is provision made for such situations? If so, how does it
differ from MTU? Or does it defer all packet-splitting to the lower
levels? Are there any bottom-level protocols that don't split transfers
into packets?

totally ignorant of ipv6, and not very knowledgable about _any_ networking,

John Perry

A large file, such as that 50 MB one you mentioned, is already split
into small chunks by the transmitter, typically at 1500 bytes or so.
The purpose of fragmentation was so that links with different size MTU
could work together. So, for example, a 1500 byte packet would be split
into 3 pieces, so that it could travel on a link with only a 576 byte
MTU. Further fragmentation may take place if an even smaller MTU is
encountered. All the pieces are then reassembled at the destination.
With IPv6, path MTU discovery is used, which will determine the maximum
MTU that can pass along the entire path, thus avoiding fragmentation
along the way. The big problem with fragmentation is the work load it
places on the routers along the path.

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