From: nenad pudar (nenad.pudar@gmail.com)
Date: Sun Sep 11 2005 - 14:41:02 GMT-3
I worked sometime ago on the project called Mcore which was introducing
JUNIPER core routers running mpls and ldp and no bgp in core network and
this worked fine.
This not Cisco feature and it has to do with how packet is forwarded in mls
network (as opposed to traditional ip forwarding:lookup in which at each hop
router is looking for source#destinantion pair)
Forwarding in mpls network is done on one (only ip over mpls) two (mpls
vpns,Cisco 6PE etc) or 3 (mple vpn with ldp over Traffic Engineering Tunnel
etc)
In any of the cases above P routers look only at the top label (in first
scenario the only one) which uniquely defies the agrees PE router ,local
label associated with it and outgoing interface .Then the router just swap
the labels and forward the packet toward PE router.
So the P router does not need to have any routing information about final
destination.
Once the label is removed on PE (or hop before if PHP is used) the PE router
will do the the lookup and look for the final bgp destination or look at
second(third) label in the case of mpls vpn or other application running on
top of mpls
AS long as you do not have any v4 connection on P router (customer ,peer
etc) you do not need BGP on it.
nenad
On 9/11/05, Rick <rick@iptool.net> wrote:
>
> I see at least 3 post to this thread that said this is a "feature" of MPLS
> "NOT" a Cisco feature and therefor since Alcatel and Juniper support the
> MPLS standards they can have a BGP free core. I am not sure what you still
> want answered.
>
> Rick
> Why is Juniper considered evil? Juniper has forced Cisco to finally build
> a
> solid SP router in the CRS.
>
>
> ----- Original Message -----
> From: "Richard Dumoulin" <Richard.Dumoulin@vanco.fr>
> To: "'ccie 2005'" <cui666@gmail.com>; <ccielab@groupstudy.com>
> Sent: Sunday, September 11, 2005 5:38 AM
> Subject: RE : RE : Cisco MPLS
>
>
> > Hi Pat,
> >
> > thx for the explanation but I already knew this. The question remains
> > unanswered. I quote you " I would be REALLY surprised that
> > Juniper, Alcatel or other vendors in this game would not see it" --> I
> would
> > just like the answer to this.
> >
> > Now let me correct some of your sentences below. In step 1 when the
> packet
> > arrives at peer1, the router does not look at his routing table but at
> his
> > CEF table. Then it imposes the label which also corresponds to peer2 BGP
> ip
> > address or BGP next hop.
> >
> > In steps 2,3 and 4 peer2 looks at its LFIB table in order to swap
> labels.
> > Peer2 is supposed to not have any BGP table so how would it do a
> recursive
> > BGP lookup? At least in a Cisco based network. The LFIB would is created
> > from 2 tables: the LIB and the RIB (derived form an IGP).
> >
> > Finally, in step 6, the operation is such that peer2 will never have to
> > perform 2 lookups. Either it will consult its CEF table because of PHP
> or
> > its LFIB.
> >
> > All this started in my head because I did hear rumours that Juniper P
> > routers needed a full routing table in order to label switch BGP
> destination
> > packets, that is all. Now this still remains unanswered.
> >
> > Also I did not say it was magic but just found the concept amazing and
> > wonderful. I very much like MPLS and I am just starting to appreciate it
> > although I did a lot of work with it when I was working for GlobalOne in
> > Spain 5 years. It was the first MPLS network in the country by then!
> >
> > -- Richard
> >
> >
> >
> > -----Message d'origine-----
> > De : ccie 2005 [mailto:cui666@gmail.com]
> > Envoyi : dimanche 11 septembre 2005 05:46
> > @ : ccielab@groupstudy.com
> > Objet : Re: RE : Cisco MPLS
> >
> > let me try to explain this using packet walkthrough, imagine this;
> >
> > peer router1(igp/bgp/mpls) - p1(igp/mpls)-p2(igp/mpls)-peer
> > router2(igp/bgp/mpls) - customer router(ebgp with peer2)
> >
> > peer router #1 and #2 have full bgp routing table, p1 and p2 only have
> > isp's internal IGP routes and mpls lsp table based on igp. a packet
> > trying to get to customer router from peer router 1, and here are the
> > steps:
> >
> > 1. packet arrived at peer1 as ipv4 packet, looking at ip routing
> > table, and a bgp route learned from peer2 indicates that the packet
> > has to be delivered to peer2 router in order to reach the destination;
> > 2. now peer1 started bgp recurisive lookup process, realized that in
> > order to reach peer2, the packet need to go to p1;
> > 3. because peer1 and p1 are running mpls in between, an mpls label
> > imposition occurred. note that the packet's destination ip is still
> > customer router's ip which p1 doesn't know;
> > 4. packet arrived at p1, will p1 look at the destination ip of the
> > packet? NO! (this is the key part), it will only look at the imposed
> > label from peer1 and use mpls pre-learned lsp table to deliver the
> > mpls packet to p2;
> > 5. p2 will look at its lsp table and deliver the packet to peer2 as
> > mpls packet or ip packet depends on whether you use PHP or not, to
> > make it simple, let's say it still sent mpls to peer2;
> > 6. peer2 receive the packet, as it's the last hop of the mpls lsp
> > path, it performed 2 things: pop the label and do ip lookup. as it has
> > the customer's route in its bgp routing table learnt via ebgp, it sent
> > the packet to customer router. end of journey!
> >
> > like I mentioned, the key step is #4, and if you really understood
> > this step, you will see there was no magic here: all because of you
> > have used mpls as transport protocol instead of ip in the core
> > network.
> >
> > And if I could see the "magic", I would be REALLY surprised that
> > Juniper, Alcatel or other vendors in this game would not see it.
> >
> > and the similar steps goes to mpls/vpn,only one more label to deal
> > with as the inner label is the indentity of the VPN, the edge PEs do
> > all the work, P routers still see the outer label without knowledge of
> > inner labels and ip info.
> >
> > to end this, MPLS is not only capable of transporting ipv4 packets,
> > but also almost everything else - ATM cells, FR frames, IPv6, Ethernet
> > frames, etc, other rfcs like martini-draft, vpls and cisco's ATOM(Any
> > Transport Over MPLS) are based on the basic concept.
> >
> > HTH,
> > Pat
> >
> >
> >
> >
> > On 9/10/05, Richard Dumoulin <Richard.Dumoulin@vanco.fr> wrote:
> > > Take the example of an ISP using an MPLS backbone. Will Juniper P
> routers
> > > need all the routes to create the LSP table? We all know that this is
> not
> > > the case with Cisco. What about the others?
> > >
> > > -- Richard
> > >
> > > -----Message d'origine-----
> > > De : Scott Morris [mailto:swm@emanon.com]
> > > Envoyi : dimanche 11 septembre 2005 04:05
> > > @ : Richard Dumoulin; 'Joe Rinehart'; ccielab@groupstudy.com
> > > Objet : RE: Cisco MPLS
> > >
> > > The LSP "routing table" is a different list all together. You CAN have
> > BGP
> > > routes present, but it's certainly not necessary to have your customer
> > > routes present.
> > >
> > > Scott
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > > Richard Dumoulin
> > > Sent: Saturday, September 10, 2005 9:19 PM
> > > To: 'Joe Rinehart'; ccielab@groupstudy.com
> > > Subject: RE : Cisco MPLS
> > >
> > > I heard that on a Juniper based MPLS network, the BGP networks needed
> to
> > be
> > > present on the P routing tables. Would be nice if anyone could confirm
> or
> > > not by having a look at the routing table...
> > >
> > > -- Richard
> > >
> > > -----Message d'origine-----
> > > De : Joe Rinehart [mailto:jjrinehart@hotmail.com] Envoyi : dimanche 11
> > > septembre 2005 02:12 @ : Richard Dumoulin; ccielab@groupstudy.comObjet
> :
> > > Re: Cisco MPLS
> > >
> > > Yes, I realize that but I was pointing out how the architecture works
> in
> > > general, most notably the IGP vs. BGP functionality. Even if you do
> not
> > > create MBGP VPNs the routing behavior is the same, with the IGP
> knowing
> > ONLY
> > > core routes and BGP just at the edges. Both protocols run separately
> with
> > > no real interaction...
> > >
> > > And as far as the AT&T network goes, yes there is a large Cisco
> component,
> > > particularly on the edges, but Avici routers are operating at the
> core.
> > The
> > > architecture is independent of the actual platforms....
> > >
> > > Joe Rinehart
> > > CCIE #14256, CCNP, CCDP
> > > Data Network Consultant
> > > AT&T Pacific Northwest Enterprise Markets
> > > ----- Original Message -----
> > > From: "Richard Dumoulin" <Richard.Dumoulin@vanco.fr>
> > > To: "'Joe Rinehart'" <jjrinehart@hotmail.com>; <ccielab@groupstudy.com
> >
> > > Sent: Saturday, September 10, 2005 2:12 PM
> > > Subject: RE : Cisco MPLS
> > >
> > >
> > > > But AT&T are using Cisco routers I believe. Also please note that I
> am
> > > > not talking about MPVPN but just about the way BGP network
> > > > destinations are label switched,
> > > >
> > > > Regards
> > > >
> > > > -- Richard
> > > >
> > > > -----Message d'origine-----
> > > > De : Joe Rinehart [mailto:jjrinehart@hotmail.com] Envoyi : samedi 10
> > > > septembre 2005 01:07 @ : Richard Dumoulin; ccielab@groupstudy.com
> > > > Objet : Re: Cisco MPLS
> > > >
> > > > Anyone feel free to jump in if I am way off base here...
> > > >
> > > > It's pretty much just a function of how the routing is set up...I
> > > > created
> > > a
> > > > mini-MPLS network on my lab rack and really was surprised to see how
> > > > the mechanics all work, especially as I tried to mimic how we have
> it
> > > > set up
> > > at
> > > > AT&T. The feature you are referring to is sometimes called a
> > > > route-free core. The label switched core itself doesn't have any
> > > > knowledge of edge
> > > (or
> > > > MPLS VPN) routes at all, they are clueless of anything outside the
> > > backbone
> > > > itself. Usually an IGP like OSPF or ISIS is run between the P nodes
> > > > in
> > > the
> > > > core and includes the PE devices too. I had one router get all buggy
> > > > because of short memory so I verified just using static routing
> across
> > > > the simulated backbone and that worked too. The core just uses IGP
> > > > and
> > > internal
> > > > routes and does the label switching from PE to PE.
> > > >
> > > > The magic is at the PE, it's pretty much doing all the heavy
> lifting.
> > > > The PE runs BGP at the edge only, peering with the CE (using eBGP)
> and
> > > > other PE's (using iBGP), and it's also responsible for creating the
> > > > MPLS VPN's using Route Distinguishers and Multiprotocol BGP. The
> core
> > > > doesnt know, doesnt care and doesnt play with BGP or the VPN's, it
> > > > just pushes
> > > traffic...
> > > >
> > > > The same would apply to Internet routes, as the BGP on the edge/PE
> > > > routers would know all of it, advertise routes, and such, but once
> > > > passed to the core P routers it would be label switched....
> > > >
> > > > It really is cool fascinating stuff.....
> > > >
> > > > Joe Rinehart
> > > > CCIE #14256, CCNP, CCDP
> > > > Data Network Consultant
> > > > AT&T Pacific Northwest Enterprise Markets
> > > > ----- Original Message -----
> > > > From: "Richard Dumoulin" <Richard.Dumoulin@vanco.fr>
> > > > To: <ccielab@groupstudy.com>
> > > > Sent: Friday, September 09, 2005 2:03 PM
> > > > Subject: Cisco MPLS
> > > >
> > > >
> > > > > There is a feature in MPLS that I find powerful and it is the
> > > possibility
> > > > of
> > > > > building an Internet backbone with 160000 routes present only in
> the
> > > > > PEs routing table. I was wondering if this was only a Cisco
> feature
> > > > > or do
> > > the
> > > > Ps
> > > > > of other vendors also support this like Juniper for example?
> > > > >
> > > > > Thx
> > > > >
> > > > > -- Richard
> > > > >
> > > > >
> > > > >
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