From: Tarun Pahuja (pahujat@gmail.com)
Date: Wed Oct 24 2007 - 13:56:25 ART
Mihai,
1) Better scalability :OSPF may not highly scale specially
if the link state database size for each attached site is big.
Further OSPF internal routes could not be summarized before
being advertised to PE which is not the case when BGP is used
as PE-CE routing protocol
2) Better PE protection: As PE device is shared among many customers, More
protection is required.
Because of distance vector behavior of BGP, it is easy to limit
the number of routes learned via CE. On the other hand when OSPF
is used as PE-CE routing protocol, PE protection could become an
issue because of link state behavior of OSPF. More specifically,
number of routes could not be relied to protect PE.
I can point out many cases where only BGP will work as a CE-PE Protocol.
Thanks,
Tarun
On 10/24/07, sheherezada@gmail.com <sheherezada@gmail.com> wrote:
>
> I agree with you that BGP is preferred because of better control of
> customer route control. In fact, all customer routers are carried in
> BGP. However, I think that the context was MPLS VPN. I don't see the
> purpose of customer route filtering in this case - the network should
> be transparent to the customer.
>
> Mihai Dumitru
> CCIE #16616 (SP, R&S)
>
> On 10/24/07, Tarun Pahuja <pahujat@gmail.com> wrote:
> > The Following documents talks about the pros and cons of using OSPF and
> BGP
> > as a Routing protocol between CE and PE in a MPLS network.
> >
> > http://tools.ietf.org/html/draft-rosen-vpns-ospf-bgp-mpls-06
> >
> > Many providers prefer BGP as it gives them better control over Customer
> > route filtering, and access to other attributes BGP has to offer.
> >
> > HTH,
> > Tarun Pahuja
> > CCIE #7707(R&S,Security,SP,Voice,Storage),CCSI
> >
> >
> > On 10/24/07, Daniel Kutchin <daniel@kutchin.com> wrote:
> > >
> > > The 32 OSPF processes limit has been lifted in the following IOS
> versions
> > >
> > > 12.3(4)T
> > > 12.0(27)S
> > > 12.2(25)S
> > > 12.2(18)SXE
> > >
> > > See this link:
> > >
> > >
> http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hirp_c
> > > /ch15/hospfvf.pdf
> > >
> > >
> > >
> > >
> > > Daniel
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > > sheherezada@gmail.com
> > > Sent: Dienstag, 23. Oktober 2007 23:26
> > > To: CCIE Abreu
> > > Cc: ccielab@groupstudy.com
> > > Subject: Re: BGP vs OSPF
> > >
> > > In my opinion, BGP has the lowest overhead, because you don't run yet
> > > another routing process on the PE (and you don't have to
> > > redistribute).
> > >
> > > OSPF has or had some limitations as per number of routing processes on
> > > the PE (limited at 32), with obvious implications on scalability. I
> > > am sure that you will find a document explaining this somewhere.
> > >
> > > With the OSPF redistribution in the MP-BGP and viceversa, you cannot
> > > get intra-area routes across the MPLS cloud. So if you have a direct
> > > backup link between say two VPN sites, traffic will always flow
> > > through the backup link, because intra area routes are preferred. The
> > > sham link helps you overcome this issue when you want traffic flowing
> > > across the MPLS cloud instead.
> > >
> > > HTH,
> > >
> > > Mihai
> > >
> > > On 10/23/07, CCIE Abreu <ccie.abreu@gmail.com> wrote:
> > > > Hello guys,
> > > >
> > > > This may sound like a question for the CCIE SP group, but I think it
> > > applies
> > > > here as well, since it's about BGP and OSPF.
> > > >
> > > > Can anyone explain the main reason why BGP is widely used as the
> > > protocol
> > > to
> > > > connect remote sites that are part of a MPLS network?
> > > > Since we may be running OSPF in each remote site, why can't we have
> all
> > > OSPF
> > > > all the way, let's say, having all edge routers as part of area 0?
> > > >
> > > > And what's the deal with OSPF sham links? I don't get those either.
> > > >
> > > > Thanks.
> > > >
> > > >
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