[j-nsp] MPLS issue

[Erdem Sener]

FWIW, I'd configure all ethernets with MTU 1600 as a policy and never
think about MTU again.
(including any switches in the middle as said)

Erdem

On Mon, Mar 3, 2008 at 5:11 PM, Mark Tinka <mtinka at globaltransit.net> wrote:
> On Monday 03 March 2008, Ying Zhang wrote:
>
>  > we are having a wired MPLS problem. Here is how the
>  > network looks like:
>  >
>  > end users ---- M7i ---- M120 ----ISP
>  >
>  > The mpls lsp is between M7i and M120. The problem is the
>  > end users have problems accessing certain websites, very
>  > slow or not accessible, some websites no problem at all.
>  > With MPLS disabled (OSPF only), the problem is gone. I
>  > think it is a MTU issue, tried to lower MTU on M7i user
>  > side, didn't fix it. Might also try to increase MTU  on
>  > MPLS interfaces, but not sure. Any thoughts? Very
>  > appreciated.
>
>  Yes, definitely sounds like an MTU issue.
>
>  For a single label (MPLS switching only, no VPN's or
>  anything kinky like that), you need at least 1504 bytes on
>  Ethernet.
>
>  With L3VPN's, you need 2 labels (one for the VPN and another
>  for MPLS switching). This brings you to 1508 bytes.
>
>  To this end, I've normally configured 1524 bytes at a bare
>  minimum on the interface. Note, however, that both the
>  router port and adjacent Ethernet switch need to be
>  configured for higher MTU's, otherwise you'll experience
>  the symptoms you describe above.
>
>  Cheers,
>
>  Mark.
>
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