PPPoE & MTU

[Hummercellc]

So I was playing around with my MTU on my router and found the following:

When MTU is set to 1492 (Router Default) On average I have between 2-10% packet loss and get
sub 1mbps download speeds....

Setting my MTU to Cisco's recommendation of 1440 for PPPoE LLC/ATM I get no packet loss and speeds are over 3mbps every time.

No from what I understand or should I say, what I have read online, is that should your IMAX/DSLAM be connected via ATM which has a maximum cell MTU of 1442 a lower MTU would be better.

Should your IMAX/DSLAM be connected via ME (Metro-Ethernet) a MTU of 1492 should be better as ME's maximum cell MTU is 1500....

Could anyone correct me if I am wrong please? But I have now tested this on three of my ADSL lines and reducing my MTU to 1440 does improve my speed, latency & reduces my packet loss.

I do know for a fact that our IMAX is backhauled with a ATM connection so this might not work for everyone but I would be interested to hear what others have to say.

 

[Pada]

1440 sounds correct if you're running an IPSec/PPTP tunnel over PPPoE (MTU of 1492) over ADSL. See http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml

So typically for a residential ADSL user you'll leave the MTU on 1492, but if you're like an MWEB Business ADSL user, which runs an IPSec tunnel over PPPoE, you'll use the MTU of 1440 (or perhaps lower even?).

I'm not entirely sure what the MTU should be on the Metro-Ethernet stuff though...

 

[SocketRocket olo]

tl;dr
420

url]http://www.cisco.com/en/US/tech/tk827/tk369/technologies_white_paper09186a00800d6979.shtml[/url]

Nice link (the colourful diagrams stopped my brain from ragequitting)

So would it mostly only apply to business accounts ? Also would there be a way to find out whether your IMAX/DSLAM is connected as ATM / ME ?

 

[Tinuva]

I'm not entirely sure what the MTU should be on the Metro-Ethernet stuff though...

Depends on the ISP lighting up the fibre. Metro-Ethernet, like Ethernet, can go up to 10000 MTU, although if you run at the default of the equipment, it probably runs at 1500.

Generally speaking, if the network supply MPLS-VPNs ect to clients, they will run at higher than 1500 mtu, so that the client can use 1500 without any problems.

 

[nerf]

I tried running my PPPoE session with a 1500 mtu and seems to work fine, slightly better it seems, pages seem to open faster.

I running a 4 mbps afrihost account over a 5 mbps line