From: Arun Arumuganainar (aarumuga@hotmail.com)
Date: Tue Jul 19 2005 - 13:24:09 GMT-3
In real world , if you redistribute BGP routes in to IGP then you are asking
for trouble . You can easily bring down your network by doing this .
Pls. Note : IGPs like OSPF and ISIS are not designed to handle huge number
of routes in the internet as it exists today .
Solution is simple : Runn Full mesh IBGP with synchronization turned off .
Black Holing will not happen this way .Alternate way to avoid Full mesh IBGP
connectivity is to runn MPLS inside core .
Pls. note : If you redistribute BGP routes in to IGP , Full mesh
connectivity is not an requirement .
Thanks and Regards
Arun
----- Original Message -----
From: "Brian McGahan" <bmcgahan@internetworkexpert.com>
To: <ccie2004@excite.com>; <oletu@inbox.lv>; <ccielab@groupstudy.com>
Sent: Tuesday, July 19, 2005 8:51 PM
Subject: RE: BGP synchronization
> The real world answer is simply to run BGP on all devices in the
> transit path. This problem only exists if you are a transit AS,
> otherwise you can skip BGP and do default routing.
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987 x 705
> Outside US: 775-826-4344 x 705
> 24/7 Support: http://forum.internetworkexpert.com
> Live Chat: http://www.internetworkexpert.com/chat/
>
> ________________________________________
> From: ccie2004@excite.com [mailto:ccie2004@excite.com]
> Sent: Tuesday, July 19, 2005 6:58 AM
> To: Brian McGahan; oletu@inbox.lv; ccie2004@excite.com;
> ccielab@groupstudy.com
> Subject: RE: BGP synchronization
>
> Hi All,
>
> Thx for your input on this.
>
> Godswill,
>
> I think as Brian has pointed out the synch issue is basically to prevent
> blackholing of traffic. The underlying concept is that if the IGP is not
> fully converged than do not advertise the route to your EBGP peer.
> Please feel free to correct me if I am incorrect on this.
>
> All,
>
> I was trying to get a real world answer on how in Transit AS's today
> this issue is dealt with (even with sync disabled we still have to
> figure out a way to prevent blackholing. I don't believe there is a way
> around that. Is There?). We see that with MPLS VPN's etc it eliminates
> the need for your core routers to run IBGP. But in traditional networks
> is this limitation still there. Does anyone(ISP's) actually redistribute
> BGP into their IGP. I just can't seem to grasp how is the situation
> dealt with because every solution I can think of has some problems or
> the other. Can someone provide an example of this being dealt with in
> real world networks.
>
>
>
>
>
> --- On Tue 07/19, Brian McGahan < bmcgahan@internetworkexpert.com >
> wrote:
> From: Brian McGahan [mailto: bmcgahan@internetworkexpert.com]
> To: oletu@inbox.lv, ccie2004@excite.com, ccielab@groupstudy.com
> Date: Tue, 19 Jul 2005 02:17:25 -0400
> Subject: RE: BGP synchronization
>
> Godswill,
>
> Yes, the problem synchronization is designed to prevent is the
> dropping of traffic by non-BGP speaking routers in the transit path. In
> order to prevent this the logic of synchronization is that if the route
> is installed in the IGP table all routers in the transit path (which
> should logically be running IGP) will have a route to the final
> destination. The solution is as you said, to suppress bestpath
> selection (and hence advertisement) if an IGP match is not found for the
> iBGP learned prefix.
>
>
> HTH,
>
> Brian McGahan, CCIE #8593
> bmcgahan@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987 x 705
> Outside US: 775-826-4344 x 705
> 24/7 Support: http://forum.internetworkexpert.com
> Live Chat: http://www.internetworkexpert.com/chat/
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Godswill Oletu
> > Sent: Monday, July 18, 2005 2:13 PM
> > To: ccie2004@excite.com; ccielab@groupstudy.com
> > Subject: Re: BGP synchronization
> >
> > I am trying to follow your logic, but I am finding it difficult to
> > reconcile
> > this line...
> >
> > ".....Synch is supposed to address the issue of a router in the middle
> of
> > your network which is not running IBGP and hence does not know how to
> get
> > to
> > a particular network that your IBGP routers are aware of....."
> >
> > Is that the issue that Synchronization really addressed?
> >
> > I think with BGP Synchronization, when an IBGP peer gets an update for
> a
> > route from another IBGP peer, it looks into its local IGP routing
> table,
> > if
> > that route is present, he is free to advertise it to other BGP Peers,
> if
> > otherwise, he will refrain from advertising it. In this scenerio, all
> > internal routers do not have to necessary run IBGP.
> >
> > To fulfill the requirements of BGP Synchronization, your IGP should be
> > aware
> > of all the routes in your network, so that when these routes become
> > available to BGP, it can accept them and send them out to external BGP
> > neighbors.
> >
> > eg
> >
> > interface fastethernet0/0
> > ip address 120.1.1.1 255.255.255.0
> > !
> > interface fastethernet0/1
> > ip address 10.1.1.1 255.255.255.0
> > !
> > ip route 50.0.0.0 255.0.0.0 120.1.1.1
> > !
> > router bgp 120
> > network 120.1.1.0
> > network 10.1.1.0
> > network 50.0.0.0
> > network 60.0.0.0
> > network 70.0.0.0
> > !
> > end
> >
> > You see that, BGP will not advertise networks 60.0.0.0 & 70.0.0.0,
> because
> > according to the limited configuration above, there is no reference to
> > them
> > in the router's routing table, but if you disable syncronization, BGP
> will
> > accept these networks and advertise them, despite the fact that none
> of
> > your
> > routers know how to reach those networks.
> >
> > You can see that, if your BGP router advertise networks 60.0.0.0 &
> > 70.0.0.0,
> > there will be problem if traffic is sent to you destined for those
> > networks,
> > I believe this is the very problem BGP synchronization is setup to
> > prevent.
> >
> > Others can contribute, so that we can all learn, if this is not what
> your
> > question is about, you can throw in more light.
> >
> > my 0.2
> >
> > Note:
> > There are many other methods of making routes available to your BGP
> > router,
> > the network statement used above is just one of them.
> >
> > ----
> > Godswill Oletu
> >
> >
> > ----- Original Message -----
> > From:
> > To:
> > Sent: Monday, July 18, 2005 2:01 PM
> > Subject: BGP synchronization
> >
> >
> > > Hi All, I just came up with a question on BGP which I have been
> asking
> > > myself but just can't seem to get a handle on. It has to do with BGP
> > > Synchronization. I know this has been beaten to death and newer IOS
> > > versions have it disabled however my question is a combination of
> the
> > > underlying issue that Synch is supposed to address and Best
> Practises.
> > > Synch is supposed to address the issue of a router in the middle of
> your
> > > network which is not running IBGP and hence does not know how to get
> to
> > a
> > > particular network that your IBGP routers are aware of. BGP Best
> > practises
> > > say that never redistribute your EBGP learnt routes into your
> interior
> > > routing protocol. Thinking along those lines and if I am right how
> > exactly
> > > would you get reachability across your network. Would you use
> default
> > > routes on your non-BGP speaking routers or are there any other
> design
> > type
> > > fixes that I am missing. thx
> > >
> > > _______________________________________________
> > > Join Excite! - http://www.excite.com
> > > The most personalized portal on the Web!
> > >
> > >
> _______________________________________________________________________
> > > Subscription information may be found at:
> > > http://www.groupstudy.com/list/CCIELab.html
> >
> >
> _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
> ________________________________________
> Join Excite! - http://www.excite.com
> The most personalized portal on the Web!
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sun Sep 04 2005 - 17:00:30 GMT-3