[c-nsp] MPLS MTU

[Sergio D.]

hey thanks. I been using MPLS for a while I just started using Cisco
as I am new to this network, I knew of this short coming. thank god
for the adjust mss command that didn't exist in Juniper. Anyway, how
would I check the current MTU for the PHYSICAL interface, so the
actual ethernet MTU, and how would I change that?
Thanks again,

On 11/14/06, Lasher, Donn <DLasher at newedgenetworks.com> wrote:
>
> Welcome to mpls. :)
>
>
> You have to make sure that ALL Devices, L2, are able to support the
> larger MTU. On older catalyst, you set the MTU on the port, on newer on
> the whole switch.
>
> Then you can raise the MPLS MTU on the router interfaces. I'd recommend
> as big as the L2 devices allow, to avoid any future issues.
>
> Good luck..
>
>
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Sergio D.
> Sent: Tuesday, November 14, 2006 9:14 AM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] MPLS MTU
>
> Hello folks,
>
> Some of our customers recently ran into some problems browsing and
> pinging with over 1468. We fixed the browsing issue by adjusting MSS on
> the incoming interfaces. It turns out that our core tag-switching
> interfaces were set at the default 1500 which in turn allowed only a
> 1496 or 1492 IP payload depending on how many labels.
>  So now we are changing the MPLS mtu to 1508, but on Cisco's website it
> mentions the following :
> "Setting the MPLS MTU to a high number can lead to packets being dropped
> on some devices, because the labeled packet is larger than the interface
> physical MTU."
>
> A lot of our core is FE interfaces, I don't have a way to test this
> before, wouldn't just automatically raise the physical MTU?
> So after raising this an FE MTU goes to 1526? 1508 MPLS + 18 Vlan +
> ethernet header?
> Thanks,
>
> --
> Sergio Danellli
> JNCIE #170
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>
>


-- 
Sergio Danellli
JNCIE #170