From: Todd, Douglas M. (DTODD@PARTNERS.ORG)
Date: Thu Aug 23 2007 - 16:29:35 ART
From what I understand if you have a 1500 byte packet payload which is the
max
mtu allowed through most networks. To add a tag or stacked tag you will need
to
increase the mtu 4bytes to hold the tag. Most people just go to set the mtu
to
say 1530 or close to that to make sure that there is no issue with tags or
tag
stacks.
DMT
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Content-class: urn:content-classes:message
Subject: Re: Question for you ISP guys
Date: Thu, 23 Aug 2007 13:59:55 -0400
Message-ID: <2c05a3070708231059h18423603o2ad5cc687d0b873f@mail.gmail.com>
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Thread-Topic: Question for you ISP guys
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From: "Gregory Gombas" <ggombas@gmail.com>
Sender: <nobody@groupstudy.com>
To: "Brian McGahan" <bmcgahan@internetworkexpert.com>
Cc: "Cisco certification" <ccielab@groupstudy.com>
Reply-To: "Gregory Gombas" <ggombas@gmail.com>
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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