Fri Apr 01, 2005 11:40 pm
The routing does add a penalty.
However with EoIP which is ethernet packets encapsulated over GRE IP packets.
The maximum sized Ethernet packet is 1514 (not including vlan header).
And you have to send this over a protocol that can have a maximum payload of 1460 (that's not counting the GRE header).
This will result in that you need to send two IP packets for a single ethernet fullsized frame. These packets must then be put in their own ethernet frame pr. hop. The fragments are then sent across and the receiving end has to wait for both frames before it can reassemble the single ethernet frame. This incurrs both latency AND it increases your packet count. To top this 802.11 protocol (be it A,B or G) has to ack each frame sent adding more latency (and the odd occurring retransmissions).
BUT it is quite efficient for it's own use (combining two ethernet lans into one over IP).
WDS does add some overhead but this overhead is very little compared to EoIP. First off it's ethernet inside ethernet (so no added IP headers and subprotocol headers). The payload does not need to be fragmented (you can send pretty large ethernet frames over 802.11).
And this is quite efficient for this exact use.
I am currently hoping mikrotik will add oversized frame support for their ethernet cards (and my favourite brand Intel). Intel cards atleast can send ethernet frames up to 2000 bytes in size (and so can many others too). Most mid-level to high-level switches support forwarding over ethernet frames up to atleast 1600 or even more.
If this support was added to Mikrotik RouterOS we could run networks where EoIP would be even more efficient.
Most carriers (around here atleast) support larger frames so they can use technologies like QinQ, MPLS or EoIP like protocols.