[ILUG] Linux Router + DSL

[Paul Jakma]

On Mon, 18 Oct 2004, Thomas Bridge wrote:

> For the purpose of this conversation there's no difference. 
> Eircom can make no assumptions about vendors (and although Cisco 
> will happily accept MTU of 1500 for PPP over L2TP, when it's PPPoE 
> they insist on 1492).

Oh yum.

> Also, far more importantly, we had a serious issue when we first 
> resold L2TP products with cheap ass CPE equipment that didn't like 
> the fact we were looking for a higher MTU.  Hence why it's sent to 
> 1492.

Double yum.

> Listen, the amount of pain I've had with Eircom and MTU sizes in 
> the last month would keep a dominatrix in business for weeks.  Get 
> me drunk when I leave (this Friday) and I'll tell you all.

Ok :)

> Where the assumption it's a direct link from the Eircom BAS to the 
> OLO BAS?

I dont know, I accept it may traverse ethernets both inside eircom, 
and at the real-ISP (ie OLO?).

> Also, the fact that Eircom's network may support jumbo frames 
> doesn't mean the OLO's BAS will.  And Eircom in fairness have to 
> support the LCD.

They could support all of them, up to whatever MTU they can handle 
internally, but this is Eircom we're talking about I guess. :(

> Actually, IOS is setting the MTU, not an admin thing.  And I'm not 
> hiking up the configuration on the BAS just to suit you - 
> especially in my last week :)

Oh, go on ;)

> However, as we're not hardcoding the MTU in this case, play with it
> and see what happens.

You sure? I have a vague memory your side wont play ball if my pppd 
tries to negotiate MTU/MRU.

> As always in this situation, if it breaks, you get to keep both
> pieces and support will be out of glue when you call!

;)

> Thomas

Anyway, 1492 bloody MTU, arg! And worse:

# ifconfig ip.tun0 | grep mtu
ip.tun0: flags=10008d1<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST,IPv4> mtu 1419 index 8

I had an awful time with my IPSec tunnel for a long while until a 
colleague added automatic MTU detection for IP tunnels to Solaris - 
up to which time 1420 had been lowest i'd tried manually setting my 
MTU (figuring it couldnt be lower) before deciding it couldnt be an 
MTU problem anymore...

More MTU please Igor!

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
"The medium is the message."
-- Marshall McLuhan