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Author Topic: MTU (yet again) and modest baby jumbo packets  (Read 1019 times)


  • Senior Kitizen
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  • Retd s/w dev; A&A; 3x7km lines; Firebrick; IPv6
MTU (yet again) and modest baby jumbo packets
« on: June 03, 2019, 03:30:49 AM »

I’m sure we’ve discussed this a thousand times before, but I feel that my understand is still somewhat lacking. If I were to send a packet say 1550 bytes long DSL towards a server that is co-located at my ISP AA how far could I get? The obvious answer is to try it. However that doesn’t answer the real question, which is: how far could I get if one or two things were reconfigured optimally. I seem to remember a mention somewhere of BT kit being able to handle 1600 byte xx[?]-PDUs in order to be able to cope with certain amounts of header bloat. This was in connection with VDSL3. Does that ring any bells?

So if I were in control of both ends, could I get away with slightly larger baby jumbo PDUs without intermediate nodes spoiling my fun? One example: say I want to send 1500-byte IPv6 PDUs as the payload of a IPv6 in IPv4 static proto 41 tunnel so that immediately makes it a 1520 byte long IPv4 PDU. Another example would be IPvx in L2TP.