More elucidation: This assumes you're using router loopback addresses as your next hops. BGP doesn't care how you get to your loopbacks, just so that you *can* get to them. If your network is designed with redundant paths to each loopback, and the state of those paths is handled by OSPF, BGP will never know there was a link state change, and your customers won't drop a packet. (Assuming, of course, that OSPF can instantly recognize that a link is down - no problem with point-to-point Ethernet-type interfaces, but there are some OSPF enhancements that solve that problem for link layers that don't give an instant indication of problems.)

On 08/27/2016 03:19 PM, Bruce Robertson wrote:
But why even go there? OSPF is a *link state* protocol. BGP is designed for passing prefixes around *regardless* of the link state. Use each protocol for what it was meant for, and happiness will ensue. Do you really want customer reachability information propagating throughout your entire network? All you need is OSPF propagating link state, which is relatively a much smaller size of possibilities. BGP then stays stable, and doesn't even notice the change. What if one router has hundreds of customers with unique (non-pool) customers on it? OSPF will propagate *all* of these customers on every link state change. BGP won't send a single update.

On 08/26/2016 03:01 PM, Faisal Imtiaz wrote:
>>As you grow, you'll find it won't scale well.

Care to elaborate more on this ?

By definition it is pointed out that putting hundreds of routers or hundreds of routes are a weak point of OSPF, however there are many different techniques available to manage that.

Regards.

Faisal Imtiaz
Snappy Internet & Telecom
7266 SW 48 Street
Miami, FL 33155
Tel: 305 663 5518 x 232

Help-desk: (305)663-5518 Option 2 or Email: supp...@snappytelecom.net

------------------------------------------------------------------------

    *From: *"Bruce Robertson" <br...@pooh.com>
    *To: *af@afmug.com
    *Sent: *Friday, August 26, 2016 5:23:14 PM
    *Subject: *Re: [AFMUG] (OSPF + ibgp) / formerly Mikrotik OSPF
    weirdness

    As you grow, you'll find it won't scale well.

    On 08/26/2016 02:21 PM, George Skorup wrote:

        I do redist with OSPF. It works fine if you know what you're
        doing. MT OSPF used to act really stupid until ROS v6.27 or
        thereabouts.

        On 8/26/2016 2:16 PM, Faisal Imtiaz wrote:

            So just for the sake of a technical discussion...

            In your opinion, what is the merit of such a config (osfp
            + ibgp) ?

            It can be argued that such a config,
              a) Still depends on OSPF functioning.
              b) Layer an additional dynamic protocol on top of it (ibgp)
              c) Requires additional  Routers (route reflectors).

            If the merit of such an approach is to manage manage OSFP
            behavior in a  more granular fashion,  Why not use the
            those features as they are available in  OSPF / Best
            Practices...
               (OSFP  best practices, suggest that, don't advertise
            connected or static routes, setup all interfaces as
            passive, and control prefix advertisements via the
            network section of OSPF).

            OSPF also tends to be the most common denominator
            (protocol) across different mfg.  Bgp being the 2nd.

            Regards

            Faisal Imtiaz
            Snappy Internet & Telecom
            7266 SW 48 Street
            Miami, FL 33155
            Tel: 305 663 5518 <callto:305%20663%205518> x 232

            Help-desk: (305)663-5518 <callto:%28305%29663-5518>
            Option 2 or Email: supp...@snappytelecom.net

            
------------------------------------------------------------------------

                *From: *"Jesse DuPont" <jesse.dup...@celeritycorp.net>
                *To: *af@afmug.com
                *Sent: *Friday, August 26, 2016 12:03:58 AM
                *Subject: *Re: [AFMUG] Mikrotik OSPF weirdness

                Right, PTP and loopback prefixes are distributed with
                OSPF (and possibly management subnets for radios) and
                "access" network prefixes (customer-facing) are
                distributed via iBGP.
                I have two of my routers configured as BGP route
                reflectors and all other routers peer with only these
                two; this solves the full mesh and provides redundancy.

                *Jesse DuPont*

                Network Architect
                email: jesse.dup...@celeritycorp.net
                Celerity Networks LLC

                Celerity Broadband LLC
                Like us! facebook.com/celeritynetworksllc

                Like us! facebook.com/celeritybroadband

                On 8/25/16 8:40 PM, David Milholen wrote:

                    He may have meant only have the ptp and loopback
                    addresses listed in networks



                    On 8/25/2016 9:31 PM, Mike Hammett wrote:

                        I've heard this concept a few times now. I'm
                        not sure how only using OSPF for the
                        loopbacks works.



                        -----
                        Mike Hammett
                        Intelligent Computing Solutions
                        <http://www.ics-il.com/>
                        
<https://www.facebook.com/ICSIL><https://plus.google.com/+IntelligentComputingSolutionsDeKalb><https://www.linkedin.com/company/intelligent-computing-solutions><https://twitter.com/ICSIL>
                        Midwest Internet Exchange
                        <http://www.midwest-ix.com/>
                        
<https://www.facebook.com/mdwestix><https://www.linkedin.com/company/midwest-internet-exchange><https://twitter.com/mdwestix>
                        The Brothers WISP
                        <http://www.thebrotherswisp.com/>
                        <https://www.facebook.com/thebrotherswisp>


                        
<https://www.youtube.com/channel/UCXSdfxQv7SpoRQYNyLwntZg>
                        
------------------------------------------------------------------------
                        *From: *"Bruce Robertson" <br...@pooh.com>
                        *To: *af@afmug.com
                        *Sent: *Thursday, August 25, 2016 6:28:43 PM
                        *Subject: *Re: [AFMUG] Mikrotik OSPF weirdness

                        I've said it before, and been argued with...
                        this is one of many reasons why you use iBGP
                        to distribute {customer, dynamic pool, server
                        subnets, anything} routes, and use OSPF
                        *only* to distribute router loopback
                        addresses.� All your weird OSPF problems
                        will go away.� My apologies if I'm
                        misunderstanding the problem, but my point
                        still stands.

                        On 08/25/2016 10:22 AM, Robert Haas wrote:

                            Alright, this problem has raised it head
                            again on my network since I started to
                            renumber some PPPoE pools.

                            Customer gets a new IP address via PPPoE
                            x.x.x.208/32 (from x.x.x.192/27 pool).
                            Customer can�t surf and I can�t ping
                            them from my office:

                            �

                            [office] � [Bernie Router] �
                            [Braggcity Router] � [Ross Router] �
                            [Hayti Router] � [customer]

                            �

                            A traceroute from my office dies @ the
                            Bernie router but I am not getting any
                            type of ICMP response from the Bernie
                            router ie no ICMP Host Unreachable/Dest
                            unreachable etc � just blackholes after
                            my office router.

                            A traceroute from the Customer to the
                            office again dies at the Bernie router
                            with no type of response.

                            �

                            Checking the routing table on the Bernie
                            router shows a valid route pointing to
                            the Braggcity router. It is also in the
                            OSPF LSA�s.

                            --

                            Another customer gets x.x.x.207/32 and
                            has no issue at all.

                            �

                            --

                            Force the original customer to a new ip
                            address of x.x.x.205/32 and the service
                            starts working again.

                            �

                            --

                            �

                            Now � even though there is no valid
                            route to x.x.x.208/32 in the routing
                            table � traffic destined to the
                            x.x.x.208/32 IP is still getting
                            blackholed.. I should be getting a
                            Destination host unreachable from the
                            Bernie router.

                            �

                            This is correct the correct response .206
                            is not being used and there is no route
                            to it:

                            C:\Users\netadmin>ping x.x.x.206

                            �

                            Pinging x.x.x.206 with 32 bytes of data:

                            Reply from y.y.y.1: Destination host
                            unreachable.

                            Reply from y.y.y.1: Destination host
                            unreachable.

                            �

                            Ping statistics for x.x.x.206:

                            ��� Packets: Sent = 2, Received =
                            2, Lost = 0 (0% loss),

                            �

                            C:\Users\netadmin>tracert 74.91.65.206
                            <callto:74.91.65.206>

                            �

                            Tracing route to
                            host-x.x.x.206.bpsnetworks.com [x.x.x.206]

                            over a maximum of 30 hops:

                            �

                            � 1���� 6 ms���� 6
                            ms���� 7 ms� z.z.z.z

                            � 2���� 6 ms���� 6
                            ms���� 6 ms� y.bpsnetworks.com
                            [y.y.y.1]

                            � 3� y.bpsnetworks.com [y.y.y.1]
                            �reports: Destination host unreachable.

                            �

                            Trace complete.

                            �

                            This is what I see to x.x.x.208 even
                            though it is not being used and there is
                            no route to it.

                            C:\Users\netadmin>ping x.x.x.208

                            �

                            Pinging x.x.x.208 with 32 bytes of data:

                            Request timed out.

                            Request timed out.

                            �

                            Ping statistics for x.x.x.208:

                            ��� Packets: Sent = 2, Received =
                            0, Lost = 2 (100% loss),

                            �

                            C:\Users\netadmin>tracert x.x.x.208

                            �

                            Tracing route to
                            host-x.x.x.208.bpsnetworks.com [x.x.x.208]

                            over a maximum of 30 hops:

                            �

                            � 1���� 6 ms���� 6
                            ms���� 6 ms� z.z.z.z

                            � 2���� *�������
                            *������� *����
                            Request timed out.

                            � 3���� *�������
                            *���� ^C

                            �

                            --

                            �

                            I�ve verified there is no firewall that
                            would affect the traffic � I even put
                            an accept rule in the forward chain for
                            both the source and destination of
                            x.x.x.208 and neither increment at all.
                            So the traffic is not even making out of
                            the routing flow and into the firewall..

                            �

                            Any pointers are where to start
                            troubleshooting next?




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