[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [RRG] A data point on transit MTU size
On 24 sep 2008, at 19:15, Templin, Fred L wrote:
I'm not convinced as to how "large" the buffers need to
be? AFAICT, the size depends on the number of simultaneous
reassemblies in progress
Right. But:
1. This could be a large number. Assume every full size packet is
fragmented then the number of fragments held at any given time is
pretty much number of ITRs we talk to / 2
2. It's possible to exhaust limits in this area for DoS purposes
Having fixed size per standard makes it much simpler. Don't
have that for IP.
The most we will ever ask the ETR to reassemble is 2KB. Ever.
Obviously we want the system to be able to handle packets bigger than
2k if hardware limitations permit, but the only reason for reassembly
would be the case where the inner packet is 1500 bytes DF=1 so you
would never have to reassemble more than two fragments, can require
that those arrive in order, too. Another optimization: require that
the first fragment is 1024 or 800 bytes or so rather than 1500, so the
reassembly buffer only needs to be 1k per session.
--
to unsubscribe send a message to rrg-request@psg.com with the
word 'unsubscribe' in a single line as the message text body.
archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg