The MPLS-OPS Archive

[Vic Nowoslawski <vnowoslawski@mac.com>]

MTU is advertized by RSVP-TE, in the SENDER_TSPEC object of the path message.

At 05:38 PM 2/22/2002 +0100, Robert Raszuk wrote:

>Krzysiek,
>
>No. The MTU in the output of "show mpls forwarding-table X.X.X.X.
>detail" has nothing to do with MTU :). The term "MTU" there is a
>misnomer, it should be actually a maximum receive unit.
>
>If the "MTU=" there is xyz then it implies that a labeled packet of size
>xyz bytes can be *received* by the router and sent out on interface
>indiacted without needing to fragment it. the MTU printed out depends on
>each prefix and could have different values depending on how many labels
>are pushed/popped.
>
>It also has nothing to do with LDP. LDP at least for now does not
>advertise MTU :). I am assuming you are talking about extensions
>proposed in: draft-black-ldp-mtu-extensions-00.txt right ?
>
>R.
>
>
> > Krzysztof Szarkowicz wrote:
> >
> > Check what MTU size is advertised by your LDP protocol (show mpls 
> forwarding-table X.X.X.X. detail)
> >
> > Regards,
> > Krzysztof Szarkowicz
> >
> > ----- Original Message -----
> > From: "Donn Lasher" <dlasher@clearskynet.net>
> > To: <mpls-ops@mplsrc.com>
> > Sent: Thursday, February 21, 2002 8:26 PM
> > Subject: MPLS & Path MTU problems
> >
> > >
> > > I've read all the MPLS-OPS archives on this issue, and tried the 
> fixes, and
> > > I'm still seeing a problem.
> > >
> > > two 3620's running 12.2.6, hooked to a 3524 switch. Multiple MPLS/Dot1Q
> > > vlan's off both routers. When traffic passing through these routers 
> from a
> > > customer to a site blocking PMTU discovery(nice long list any more), 
> it all
> > > the traffice appears to the customer to be blackholed.
> > >
> > > ip icmp debug shows:
> > >
> > > Feb 20 22:39:11 X.X.X.X 5813: 3w5d: ICMP: dst (X.X.X.X) frag. needed 
> and DF
> > > set unreachable sent to 216.221.138.92
> > > Feb 20 22:39:12 X.X.X.X 5815: 3w5d: ICMP: dst (X.X.X.X) frag. needed 
> and DF
> > > set unreachable sent to 216.221.138.92
> > >
> > > At the moment I'm applying a route-map to clear df bit on my NSP 
> connected
> > > router, but that's a hack. I'd really like to find and solve the real 
> issue.
> > >
> > > Ethernet MTU is 1500. tag-switching MTU unset (defaulting to 1500)
> > > tag-switching ip set on all interfaces
> > >
> > > I've tried setting the tag-switching mtu to 1540, making sure the switch
> > > was set mtu 2018, didn't make any difference.
> > >
> > > Thanks in advance for any help.
> > >
> > >
> > >
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> > >
> >
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Vic Nowoslawski
Tel. 703-794-8398
Cell. 703-338-7701
e-mail. vnowoslawski@mac.com

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