From: Jongsoo (bstrt2004@gmail.com)
Date: Mon Nov 07 2005 - 22:16:58 GMT-3
OK here is the second possible way
Let me give a scenario
CE1------Pe1-----Pe2--CE2
|
|
Pe3---CE3
CE1 is HQ,
CE2 and CE3 are small office.
For whatever reason( perhaps for virus checking...), CE1 need to be
a hub,
CE2 and CE3 need to be spokes. So that a direct traffic between
CE2 and CE3 is not allowed, it must go through CE1.
The second possible way I am thinking is using eBGP between CE and PE
and neighbor allow-in command. One big assumption is that neighbor
allow-in command will allow CE to readvertize the prefixes with
duplicate ASN as long as the number of ASN repeats is less than what
is configured.
Let's say
CE1( HUB), CE2(Spoke), CE3(Spoke) are in AS 1000
PE1(HUb), PE2(Spoke), PE3(Spoke) in AS100
Only two MP-BGP sessions : Only from HUB PE to Spoke PE. Not between
Spoke and Spoke.
Each CE has eBGP with local PE.
But each of CE abd PE has neighbor allow-in 2 command.
Eachspoke CE will annouce their prefixes to the local spoke PE. and
then spoke PE to HUB PE1. When HUB PE1 advertize those prefix to HUB
CE1 via eBGP, HUB CE( AS 100) will see its own ASN once like "1000
100 i ( let's just say i)" but allow-in 2 will make HUB CE1 allow
those prefixes in with ASN 100 and readvertize them back to HUB PE1,
which also see its own ASN 1000 bbut will take it due to the command,
...so finally, spoke CE will receive those prefiex with ASN 1000 100
1000 100 i and neighbor allow-in 2 command will allow those prefix in
but not to re-re-advertize because it only allow 2 duplicate.
The spoke CE that originate the route won't take them as valid route
due to shorter AS-path rule. But other spoke CE will take them as
valid route so that traffic from spoke CE to spoke CE will always via
HUB CE1? maybe not ( If I re-think, it will be via HUB PE1 not HUB
CE1 because VRF table in HUB PE1 will show the best route to Spoke is
to spoke PE not to Hub CE1...( I guess I am dead lock (: )
Can we fix it or did I tatally misunderstand this, or a little bit of both...
Jongsoo
On 11/6/05, Scott Morris <swm@emanon.com> wrote:
> Correct. As long as the spoke would route through the 0/0 route back to the
> hub, then you would achieve what you wanted.
>
> A little odd, but very workable!
>
> Scott
>
> -----Original Message-----
> From: Jongsoo [mailto:bstrt2004@gmail.com]
> Sent: Sunday, November 06, 2005 12:23 AM
> To: Andrew Lissitz (alissitz)
> Cc: swm@emanon.com; C&S GroupStudy; FORUM
> Subject: Re: We've moved to PE-CE routing! (SP-CCIE)
>
> What I am trying to do is to make two uni-direction VRF forwarding table 1)
> from spoke to hub and 2) from hub and spoke.( not from spoke to spoke
> directly)
>
> In order to prevent the connection from spoke to spoke, I think I have to
> place a route filtering to block one spoke's static routes announcement from
> MP-BGP to the other spoke's VRF...
>
> Something like this
>
> PE1
> ip vrf up
> ...
> route-target export 100
>
> ip vrf down
> ...
> route-target import 200
>
> PE2
>
> ip vrf up
> ...
> route-target import 100
>
> ip vrf down
> ...
> route-target export 200
>
> PE3
>
> ip vrf up
> ...
> route-target import 100
>
>
> ip VRF down
> ...
> route-target export 200
>
>
> If PE1 is not RR and there are only two MP-iBGP session 1) between PE1 and
> PE2 and 2) between PE1 and PE2 ( not between PE2 and PE3), then I figure I
> may not need this route-target manupulation.
>
> I am dying to lab this out. But no time. I may do rack rental I also like to
> come up with another way...
>
> Jongsoo
>
>
> On 11/5/05, Andrew Lissitz (alissitz) <alissitz@cisco.com> wrote:
> >
> >
> >
> > Hello Jongsoo,
> >
> >
> >
> > I have not labbed this up for you ... so there may be something to
> > modify or add to your config thoughts, but here goes. Your questions / my
> comments:
> >
> >
> > * Can I use the next hop address instead of interface for "ip route
> > vrf up 0.0.0.0 0.0.0.0 fe1" command ? The answer is yes. Personal
> > preference, I like to use next hop on any multi-access interface.
> > Once you added the vrf keyword to this command, you have told the
> > router which routing table to look in. The next hop address should be
> > found on a connected interface, so this is fine.
> >
> > * For traffic flow from Hub to Spoke - Once you add a static route on
> > the
> > PE2 and PE3 routers pointing the CE2 and CE3 networks, the VRF routing
> > table contains routing information to reach the networks behind CE2
> > and CE3. This is only within the PE2 and PE3 VRF route table until you
> redist into MPBGP.
> > Within the ipv4 vrf up and vrf down address families, you will need
> > to redist static. As you mentioned all PEs will learn this via MPBGP
> > and update their VRF tables as needed.
> >
> > So after PE1 knows how to reach these networks, it will send the
> > traffic to the correct PE.
> >
> > * What are we missing? Well ... in each of these case the CEs only
> > have one way to go and that is to the PE. For the Hub CE, if it runs
> > static routing, will it know where to go? A default static should be
> > added here as well as to all the CEs.
> >
> > Real world perspective ... (sorry about this) ... The hub router would
> > likely be running BGP or an IGP with the PE. In this case, the CE
> > would learn routing information dynamically. In this limited example,
> > the hub router only has one link to the ISP network... so this is more
> simple.
> >
> > Jongsoo, I did not follow the route-target comments you made. Perhaps
> > this is from when you labbed this up? No worries ... I am sure in the
> > lab this up becomes clear.
> >
> > We are all lacking my man ... especially me!!!!
> >
> >
> > ________________________________
> > From: Jongsoo [mailto:bstrt2004@gmail.com]
> > Sent: Friday, November 04, 2005 8:27 PM
> > To: swm@emanon.com; Andrew Lissitz (alissitz)
> > Cc: C&S GroupStudy; FORUM
> > Subject: Re: We've moved to PE-CE routing! (SP-CCIE)
> >
> >
> > Guys
> >
> > Thanks for the information. I am obviously lacking some "basics" about
> > MPLS VPN.
> > ( I realized I have to think multi-dimensionally to figure out routing
> > behavior among VRFs via MP-BGP and MPLS tags)
> >
> > Anyway, using the static method explained by Scott, Andrew and Arun,
> > I came up with more details hoping I get it right.
> >
> >
> > 1) Static routes only
> > PE1 is RR and all three PEs are in full-mash.
> > There are two VRFs of up( from spoke to hub) and down( from hub to
> > spoke) configured in each PE.
> >
> >
> > CE1-----VRF=down-fe1-PE1-----Pe2-fe2----VRF=Up---CE2 (
> > 10.2.2.0/24)
> > |
> > |
> > PE3
> > fe3
> > |
> > VRF Up
> > |
> > |
> > CE3( 10.3.3.0/24)
> >
> > 1-1) for a traffic flow from spoke( CE2, CE3) to Hub ( CE1) ( VRF =
> > up) In PE1 config,
> > A) put a default static route to CE1 = "ip route vrf up 0.0.0.0 0.0.0.0
> fe1"
> > ( fe1 is the out-going interface to CE1)
> > B) Redistribute the static to bgp, route-export = 100 ( due to
> > full-mash Mp-ibgp, PE2 and PE3 learn this route), In PE2 and PE3
> > A) put the interface connecting CEs to VRF=up
> > B) Import routes w/ route target =100 from MP-BGP
> > C) CE2 and CE3 have a default route to PEs
> >
> > In this way, any traffic from CE2 and CE3 should come into PE1 via
> > MPLS and go out via the fe1 interface of PE1 to CE1 Can I use the next
> > hop address instead of interface for "ip route vrf up 0.0.0.0 0.0.0.0
> > fe1" command ?
> >
> >
> > 1-2) for a traffic flow Hub to Spoke ( VRF = down)
> >
> > In PE2 config,
> > A) put a static route to CE2 = "ip route vrf down 10.2.2.0
> > 255.255.255.0 fe2" ( fe2 is an out-going interface to CE2)
> > B) Redistribute the static to bgp, route-export = 200 ( due to
> > full-mash Mp-ibgp, PE1 and PE3 learn this route but only PE1 imports
> > it), In PE3 config,
> > A) put a static route to CE3 = "ip route vrf down 10.3.3.0
> > 255.255.255.0 fe3" ( fe3 is an out-going interface to CE3)
> > B) Redistribute the static to bgp, route-export = 200 ( due to
> > full-mash Mp-ibgp, PE1 and PE2 learn this route only PE1 imports it),
> > In PE1
> > A) put the interface connecting CE1 to VRF down
> > B) Import routes w/ route target =200 from MP-BGP advertised by PE2
> > and PE3
> > C) CE1 have static routes to PE1 for ip prefix destined to CE2 and CE3
> >
> > In this way, any traffic from CE1 to CE2 or CE2 will be sent to PE1,
> > which will forward it based on VRF down routing table.
> >
> > What am I missing?
> >
> >
> > Jongsoo
> >
> >
> >
> > On 11/4/05, Scott Morris <swm@emanon.com> wrote:
> > > This is definitely fun to keep the SP list alive, although I'm
> > > surprised
> > we
> > > haven't irritated the R&S guys yet!
> > >
> > > Anyway... If I were presented a situation (again, real life
> > > thinking)
> > where
> > > someone said they wanted to essentially set the "hub" site up as a
> > > route-reflector, my first inclination would be to do static routes
> > > between the PE and CE and let their CE routers peer with each other
> > > and not with
> > the
> > > PE at all. That would seem to be a simple way of the SP saying "not
> > > my problem" and save a few headaches.
> > >
> > > Like Andrew says, the goal here is to make the CE fairly ignorant of
> > > the VRF's existance (although with allowas-in, it kinda makes that
> moot).
> > >
> > > If this were a lab scenario, you'd certainly need to look at what
> > > things
> > you
> > > were or were not allowed to do, but I'd keep it as simple as possible!
> > >
> > > Scott
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> > > Of Andrew Lissitz (alissitz)
> > > Sent: Friday, November 04, 2005 12:43 AM
> > > To: Jongsoo
> > > Cc: C&S GroupStudy; FORUM
> > > Subject: RE: "neighbor allowas-in" command ( SP CCIE)
> > >
> > > You are right Jongsoo ... I need to keep my head out of reality for
> > > the
> > CCIE
> > > prep ...
> > >
> > > As you know, for CCIE lab, so much will depend on wording of question.
> > > Thanks for the diagram, it helps.
> > >
> > > So if CE2 and CE3 must go through CE1, then these two sites must
> > > choose to route to the hub site first.
> > >
> > > Normal routing would work. Forgive me if this is boring anyone ... I
> > > am
> > just
> > > going to 'think out loud' in this email.
> > >
> > > The CE and the PE share routes. The PE keeps these routes in the
> > > VRF, the CE is (typically) ignorant of VRF and does not know what
> > > goes on within
> > the
> > > PE. Using iBGP all PEs will share this information so that any PE
> > > with
> > the
> > > same customer VRF will have a converged routing table.
> > >
> > > So depending on what you are or are not permitted to do you can
> > > focus on
> > CE
> > > or PE route manipulation. If this is done via the CE, then
> > > manipulate or filter your IGP so that the next hop is the hub. The
> > > PEs simply share
> > what
> > > they have learned, unless you have configured them otherwise.
> > >
> > > If you do this on the PEs, then filter routing information so the
> > > spoke
> > CEs
> > > think that the hub is the next hop for any where. This could be done
> > either
> > > iBGP, or if the PE and CE run a IGP between them, then filter the
> > > routing information via the PE IGP. The CE IGP will only learn what
> > > is administratively allowed.
> > >
> > > If you can redistribute a static default on the hub PE, cool. You
> > > can
> > allow
> > > only this default to the remotes and allow all | m the spokes to the
> hub.
> > >
> > > Suggestion to the group... Do you all think we should start a new
> > > email string to discuss these options? If we are done with this
> > > allowas-in discussion, then lets create another email string.
> > >
> > > Jongsoo, thanks man for keeping these emails going. You going for
> > > your SP CCIE helps us all!!!
> > >
> > >
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Jongsoo [mailto:bstrt2004@gmail.com]
> > > Sent: Thursday, November 03, 2005 8:08 PM
> > > To: Andrew Lissitz (alissitz)
> > > Cc: C&S GroupStudy; FORUM
> > > Subject: Re: "neighbor allowas-in" command ( SP CCIE)
> > >
> > > Andrew / All
> > >
> > > I totally agree about normal ISP environment. However, in CCIE lab
> > > is far beyond the normal.
> > >
> > > Let me give a scenario
> > >
> > > CE1------Pe1-----Pe2--CE2
> > > |
> > > |
> > > Pe3---CE3
> > >
> > > CE1 is HQ,
> > > CE2 and CE3 are small office.
> > > For whatever reason( perhaps for virus checking...), CE1 need to be
> > > a hub,
> > > CE2 and CE3 need to be spokes. So that a direct traffic between
> > > CE2 and CE3 is not allowed, it must go through CE1.
> > >
> > > I am looking for how many ways exist to design this topology.
> > >
> > >
> > > Thanks
> > >
> > > Jongsoo
> > >
> > >
> > > On 11/3/05, Andrew Lissitz (alissitz) <alissitz@cisco.com> wrote:
> > > > Hey Dude,
> > > >
> > > > ISPs run iBGP between PEs (more common to use RRs but same
> > > > concept), so the idea of a PE seeing it's own ASN in the path is not
> likely.
> > > > The PE may see different AS numbers repeated in the path, but what
> > > > does it care? As long as it does not see its own ASN and detect a
> > > > loop, all is well.
> > > >
> > > > Some ISPs give the customers one ASN for all the customer sites.
> > > > In this case, this problem will occur. The CE will see the routes
> > > > from the remotes sites and see it's ASN in the path. Refer to
> > > > that earlier
> > >
> > > > diagram.
> > > >
> > > > Other ISPs give the customers different ASN for each site... but
> > > > for obvious reasons this does not scale.
> > > >
> > > > So, in the case of hub and spoke (is this common, have you all
> > > > seen this in production?), each PE is running iBGP with each other
> > > > or the hub is a RR. Each PE will not see it's own ASN. Each PE
> > > > has learned BGP routes from it's CE and will pass these between
> > > > peers. Each peer will run the best path process and select the
> > > > best route. Only best routes are advertised ...
> > > >
> > > > If for some reason, your BGP speakers will see what appears to be
> > > > a loop, then allowas will work. You can also override the ASN as
> well.
> > > >
> > > > Andrew rule of thumb (does not mean much ... will not even get you
> > > > free
> > > > coffee): allowas-in would be configured on CEs because they are
> > > > receiving these routes, and as-override would be configured on
> > > > routers
> > >
> > > > advertising routes ... more than likely the PEs.
> > > >
> > > > Jongsoo, I do not feel as though I have fully answered your
> > > > question
> > > ...
> > > > Sorry about that.
> > > >
> > > > Andrew
> > > >
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> > > > Behalf Of Jongsoo
> > > > Sent: Thursday, November 03, 2005 5:06 PM
> > > > To: Andrew Lissitz (alissitz)
> > > > Cc: C&S GroupStudy; FORUM
> > > > Subject: Re: "neighbor allowas-in" command ( SP CCIE)
> > > >
> > > > When I wrote the below email, my stomach was a little empty :)
> > > >
> > > > Regarding my point 2) "advertize iBGP routes to iBGP peers (
> > > > normal behavior of iBGP is not to advertize iBGP routes to any
> > > > iBGP peers)",
> > > >
> > > > First, this thought is from CCO descprition "One Virtual Private
> > > > Network routing/forwarding instance (VRF) receives prefixes with
> > > > ASNs from all PE routers and then advertises them to neighboring
> > > > PE
> > > routers."
> > > >
> > > > I figured from the description that a PE receives a prefix with
> > > > its own ASN from PE router and advertize
> > > >
> > > > Let's say "neighbor allowas-in 1" in AS 100 in three PE's( pe1,
> > > > pe2, pe3).
> > > >
> > > > If via MP-BGP, PE1 and PE2 learn from PE3 a VPN route 10.0.0.0/24
> > > > with
> > >
> > > > as-path = null, I think PE1 will annouce back 10.0.0.0/24 with
> > > > as-path=100 to PE2 and PE3 as well as PE2 will do the same to PE1
> > > > and PE3, which is not normal iBGP behavior. But 10.0.0.0/24 with
> > > > AS-path 100 from PE1 and PE 2 can't beat 10.0.0.0/24 with as-path
> > > > null from
> > > PE3.
> > > >
> > > > But the interesting result is if PE2 is not importing 10.0.0.0/24
> > > > with
> > >
> > > > as-path=null from PE3, then PE2 will only have 10.0.0.0/24 with
> > > > as-path=100 from PE1.
> > > > This will achieve hub-and-spoke VPN topology ( PE1 = hub and PE2
> > > > and
> > > > PE3 = spokes)
> > > >
> > > > Please feel free to correct me if I am wrong.
> > > >
> > > > Jongsoo
> > > >
> > > > On 11/2/05, Andrew Lissitz (alissitz) <alissitz@cisco.com> wrote:
> > > > > Hey Buddy,
> > > > >
> > > > > Here is a live example, I have not done the hub and spoke labs
> > > > > like several others on this mail list have:
> > > > >
> > > > > CE ---bgp---PE ---(ISP Cloud)--- PE---bgp---CE
> > > > >
> > > > > Each CE runs AS 65000 and shares routes with the PE. The PEs
> > > > > share routes via iBGP. The remote PE shares routes with the
> > > > > remote CE, and the CE sees the routes from AS 65000.
> > > > >
> > > > > What is BGP to do? It sees its own AS number and realizes there
> > > > > is a problem.
> > > > >
> > > > > Solution: Either PE changes the AS number with as-override or
> > > > > the CE
> > >
> > > > > allows its own AS number to come in via the allowed-as command.
> > > > > The
> > >
> > > > > number @ the end is how many times the CE will allow it's own AS
> > > > > number to be present in the path string of the incoming route
> > > > information.
> > > > >
> > > > > Concerning your gut feelings (btw ... hope you are not writing
> > > > > on empty stomach), number one sounds good, but with number 2,
> > > > > you are essentially saying that this command will override bgp
> > > > > split
> > > horizon.
> > > >
> > > > > This is not what it will do, if a route is already coming in,
> > > > > and it
> > >
> > > > > contains the BGP's AS number in the path, then let this in. Not
> > > > > whether or not to advertise to other peers. I have not seen this
> > > > > command change BGP split horizon behavior ...
> > > > >
> > > > > BGP best path selection still occurs, it is just that the routes
> > > > > will not be rejected because of loop detection. I have not seen
> > > > > multiple routes being accepted as best paths... Can multiple
> > > > > routes exist without the BGP multipath command?
> > > > >
> > > > >
> > > > >
> > > > > -----Original Message-----
> > > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com ] On
> > > > > Behalf
> > >
> > > > > Of Jongsoo
> > > > > Sent: Wednesday, November 02, 2005 7:33 PM
> > > > > To: C&S GroupStudy; FORUM
> > > > > Subject: "neighbor allowas-in" command ( SP CCIE)
> > > > >
> > > > > I am trying to understand this command will allow to receive
> > > > > MP-bgp vpn routes with the same ASN.
> > > > >
> > > > > If I see usage guide in CCO, it says
> > > > >
> > > > > ##################################
> > > > > Usage Guidelines
> > > > > In a hub and spoke configuration, a PE router readvertises all
> > > > > prefixes containing duplicate autonomous system numbers. Use the
> > > > > neighbor allowas-in command to configure two VRFs on each PE
> > > > > router to
> > > >
> > > > > receive and readvertise prefixes are as follows:
> > > > >
> > > > > One Virtual Private Network routing/forwarding instance (VRF)
> > > > > receives prefixes with ASNs from all PE routers and then
> > > > > advertises them to neighboring PE routers.
> > > > >
> > > > > The other VRF receives prefixes with ASNs from the customer
> > > > > edge
> > > > > (CE)
> > > >
> > > > > router and readvertises them to all PE routers in the hub and
> > > > > spoke configuration.
> > > > >
> > > > > You control the number of times an ASN is advertised by
> > > > > specifying a
> > >
> > > > > number from 1 to 10. "
> > > > > ################################################
> > > > >
> > > > > In my gut feeling, basically, this command seems allow two
> > > > > things,
> > > > > 1) receive BGP routes with its own ASN from PE or CE, ( normal
> > > > > behavior of BGP blocks BGP route with its own ASN in order to
> > > > > prevent loop) and
> > > > > 2) advertize iBGP routes to iBGP peers ( normal behavior of iBGP
> > > > > is not to advertize iBGP routes to any iBGP peers).
> > > > >
> > > > > What seems interesting is this feature will creates a lot of
> > > > > redundant
> > > >
> > > > > routes but the length of AS path will quickly determine the best
> > > > > routes so that there won't be any loop...
> > > > >
> > > > > This will be a perfect command to make hub and spoke topology to
> > > > work...
> > > > >
> > > > > The biggest question I have now is " am I right or wrong?".
> > > > > Someone please correct me if I am wrong.
> > > > >
> > > > > Thanks
> > > > >
> > > > >
> > > > > Jongsoo
> > > > >
> > > > >
> > ____________________________________________________________________
> > > > > __ _ Subscription information may be found at:
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> > > >
> > > >
> > ______________________________________________________________________
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> > >
> > >
> > ______________________________________________________________________
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