From: sheherezada@gmail.com
Date: Thu Aug 23 2007 - 17:37:24 ART
Well, I think that you have your answers by now. I can only add few things:
1) Yes, the MTU has to accommodate at least two labels (8 octets), but
it is usually set higher.
2) From the BGP speakers, not all of them have to carry the full
Internet table. A customer may have a BGP session with the directly
attached PE to announce its routes and a different multihop session
with a full table router to learn the upstream AS view of the
Internet.
3) In my opinion, IS-IS does not have the area limitations and can be
tweaked better for sub-second convergence. It is also easier to
configure and immune to spoofing. Anyway, you don't need routes in
your IGP other than your loopbacks.
HTH,
Mihai Dumitru
CCIE #16616 (SP, R&S)
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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