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FTTC Modem: Difference between revisions
Introduce RFC 4638 and explain why it's needed with FTTC
m (clean up, typos fixed: eg → e.g. , 18Mb/sec → 18Mbit/s (2)) |
(Introduce RFC 4638 and explain why it's needed with FTTC) |
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=RFC 4638 Information=
When using a router with an external modem, one has to use PPPoE on the router as the connection method. This normally means that the MTU on the PPPoE link
Some pointers regarding RFC 4638, PPPoE and Linux-based routers.▼
can be no higher than 1492 octets (PPPoE has an 8 octet overhead, and the whole packets has to fit in a 1500 octet Ethernet frame). However there is a
#The wan interface needs to be set to an MTU of 1508 on the assumption that there needs to be room for the 1500 mtu PPP package on the way to the modem (1500 may work - untested though).▼
technique to use ''baby jumbo frames'' to extend the Ethernet frame size to 1508 octets and allow the full 1500 octets on the PPPoE link.
In order to use baby jumbo frames on FTTC, the customer's router must support RFC 4638. It is not enough that the router supports baby jumbo frames via
configuration, the router must be able to do the negotiation described in RFC 4638.
▲#The wan interface needs to be set to an MTU of 1508 on the assumption that there needs to be room for the 1500
#You will require the unreleased ppp 2.4.6. In testing, ppp 2.4.5 with the rp-pppoe plugin updated to the latest version seems to work, although a recompile will be necessary. This can be fetched from ppp's website / git.
#Using ppp's debug option will allow you to see the rp-pppoe plugin negotiating a PPP-Max-Payload option
Ensure you're using [[Linux|kernel 2.6.34+ or 2.6.36.3+]]
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