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Re: PMTU-D: remember, your load balancer is broken
[email protected] ("Bora Akyol") writes: > FYI, there are core routers out there that can support line rate > HW-based fragmentation. I believe this is necessary in any router > with heterogeneous interfaces. OK, somebody check me on this. "Line rate" means back to back, minimum spaced packets. Fragmentation means turning single packets into multiple packets. Each such packet will have its own headers, thus, fragmentation means turning a single header into multiple headers. Headers take space. Therefore if there's a 100Mb/s FDDI (MTU 4400) on the input side of a router, and a 100Mb/s FastEthernet (MTU 1500) on the output side of that router, then there WILL be lossage due to fragmentation, since "line rate" on the output side has more IP headers octets per IP payload octet than "line rate" on the input side did. This is a contrived example but there are more complex and more subtle flows in real life that would excite this problem. Fragmentation is like classful addressing -- an interesting early architectural error that shows how much experimentation was going on while IP was being designed. -- Paul Vixie <[email protected]> SVP for Internet Services, MFNX M.I.B.H. Inc. is a subsidiary of Metromedia Fiber Network, Inc.