From: Mounir Mohamed (mounir.mohamed@gmail.com)
Date: Thu Aug 23 2007 - 19:30:32 ART
Hello,
This is totally depending on the media type and the connections between egde
and core gears , also it's depending on the MPLS applications provided (TE,
VPN, Qos) How many labels in the label stack should tell you how much u need
to increase the MTU, because Each label added to the MPLS header add
edtional 4 bytes so if there is 3 labels in the label stack the interface
MTU should be 1500+4+4+4=1512 bytes so for each label a new 4 bytes Is added
Best Regards,
Mounir Mohamed
On 8/23/07, Gregory Gombas <ggombas@gmail.com> wrote:
>
> Thanks everyone for your responses. Do routers running MPLS need to
> increase their MTU size to accomodate the additonal overhead of the
> MPLS header or are packets over 1496 bytes fragmented?
>
> On 8/23/07, Brian McGahan <bmcgahan@internetworkexpert.com> wrote:
> > A lot of large providers run IS-IS as their IGP, BGP at the edge,
> > and then MPLS in the core. Running MPLS not only enables advanced
> services
> > like traffic engineering and L2/L3 VPNs, it also removes the requirement
> of
> > transit devices having to carry the full public BGP table. It works
> this
> > way because the MPLS enabled routers don't need to know what the final
> > destination of a packet is, only what the exit point is.
> >
> > HTH,
> >
> > Brian McGahan, CCIE #8593 (R&S/SP/Security)
> > bmcgahan@internetworkexpert.com
> >
> > Internetwork Expert, Inc.
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> >
> >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > > Gregory Gombas
> > > Sent: Thursday, August 23, 2007 10:37 AM
> > > To: Cisco certification
> > > Subject: Question for you ISP guys
> > >
> > > For those of you with ISP experience, can you tell me what routing
> > > protocols do service providers typicall run within their AS?
> > >
> > > Do you have every single router running BGP? I can't imagine
> > > redistributing 225k+
> > > routes into an IGP, so how do you pass these routes withing your AS?
> > >
> > > If you are using iBGP what are you using to transmit next hop
> > > information (as iBGP does not normally update the next hop of the
> > > external AS)?
> > >
> > > Can someone point me to some documentation showing typical ISP routing
> > > design?
> > >
> > > Thanks,
> > > Greg
> > >
> > >
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-- Best Reagrds, Mounir Mohamed
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