Re: Trying to understand OSPF Point-to-Multipoint Non-Broadcast

You can use a summary to get the /24 if required.

---------- Original Message ----------------------------------
From: Narbik Kocharians <narbikk_at_gmail.com>
Reply-To: Narbik Kocharians <narbikk_at_gmail.com>
Date: Sat, 4 Jun 2011 21:34:45 -0700

>Andrew,
>
>
>Just to add to what Bob nicely explained.
>
>
>
>Some times to know how to manipulate routes and how to take advantage of a
>given feature within a protocol, you have to know whats available to you in
>that protocol and what options (Once configured) can give you certain
>behavior that you are looking to achieve.
>
>
>
>Lets say R1 is the hub router and R2 and R3 are configured as the spokes.
>
>R2 and R3 are both advertising a network, lets say 1.0.0.0/8.
>
>
>
>R2 and R3 are advertising the same cost to R1 for network 1.0.0.0/8.
>
>R1 adds its cost to this multi-access network, and it performs a load
>balancing of some type for network 1.0.0.0/8, through R2 and R3.
>
>
>
>This is all good, but what if I told you that R2 has a connection rate of
>64Kbps and R3 has a T1 connection to the same multi-access network, I guess
>you would NOT want to perform equal cost load balancing and the interesting
>part is that none of the spokes advertise their cost to this NMBA network to
>R1. So how do you tell OSPF which spoke R1 should go through to reach
>network 1.0.0.0/8.
>
>
>
>In this case, if the network type is configured as a Point-to-Multipoint
>non-broadcast, when you configure the neighbors on R1 you will also see a
>cost option, and this cost option only shows up under this network type.
>NOW..manipulating this cost option you can tell R1 to go through the
>spoke that has a better total cost.
>
>
>
>Maybe for what you are asking or wanting to do (If i understand you
>correctly), an OSPF "Non-broadcast" network type may also be an option.
>
>
>
>
>
>I hope this helped.
>
>
>
>
>On Sat, Jun 4, 2011 at 6:30 PM, Abdullah Al-Malki
><a.almalki1402_at_gmail.com>wrote:
>
>> Hi Andrew,
>> Hub-spoke topology can better illustrate the point-to-multipoint
>> non-broadcast which is cisco proprietary.
>>
>> This mode of operation seems strange at first glance because it uses static
>> neighbor peering using the neighbor command.
>>
>> However, think of the use of the neighbor command that we can use in the
>> hub
>> to solve the asymmetric cost to spokes.
>>
>> Neighbor command can set the cost to the neighbor which allows better
>> metric
>> control.
>>
>> Regards,
>> Abdullah
>>
>> On Sun, Jun 5, 2011 at 3:59 AM, Andrew LaPorte <andy_at_cloud9.net> wrote:
>>
>> > Hi,
>> >
>> >
>> >
>> > I m hoping that someone can explain to me the way OSPF works on a
>> > Point-to-Multipoint Non-Broadcast.
>> >
>> >
>> >
>> > Let me explain the situation I m running across. I need to connect three
>> > routers using OSPF. The routers are:
>> >
>> >
>> >
>> > R1 fa0/0 (10.1.1.1/24) _-` fa0/0 (10.1.1.2/24) R2 fa0/1 (10.2.2.1/24) _
>> `
>> > fa0/1 (10.2.2.2/24)R3
>> >
>> >
>> >
>> > R1
>> >
>> > Interface fa0/0
>> >
>> > Ip add 10.1.1.1 255.255.255.0
>> >
>> > Router ospf 1
>> >
>> > Network 10.1.1.1 0.0.0.0 area 0
>> >
>> >
>> >
>> > R2
>> >
>> > Interface fa 0/0
>> >
>> > Ip address 10.1.1.2 255.255.255.0
>> >
>> > Interface fa 0/1
>> >
>> > Ip address 10.2.2.1 255.255.255.0
>> >
>> > Ip ospf network point-to-multipoint non-broadcast
>> >
>> > Router ospf 1
>> >
>> > Network 10.1.1.2 0.0.0.0 area 0
>> >
>> > Network 10.2.2.1 0.0.0.0 area 1
>> >
>> > Neighbor 10.2.2.2
>> >
>> >
>> >
>> >
>> >
>> > R3
>> >
>> > Inter fa 0/1
>> >
>> > Ip address 10.2.2.2 255.255.255.0
>> >
>> > Ip ospf network point-to-multipoint non-broadcast
>> >
>> > Router ospf 1
>> >
>> > Network 10.2.2.2 0.0.0.0 area 1
>> >
>> > Neighbor 10.2.2.1
>> >
>> >
>> >
>> > All connections are Ethernet. The restrictions given are that R2 to R3
>> > cannot form a DR/BDR relationship and they are not allowed to exchange
>> > multicast.
>> >
>> >
>> >
>> > My configuration is to use Point-to-Multipoint Non-Broadcast on the R2 to
>> > R3
>> > interfaces. When I do that I get a surprising result.
>> >
>> >
>> >
>> > I get 2 routes on R1 that are both /32 for 10.2.2.1 and 10.2.2.2 I m
>> also
>> > not getting the /24 for the 10.2.2.0/24 that I m expecting.
>> >
>> >
>> >
>> > R1 show ip route
>> >
>> > O IA 10.2.2.2/32 [110/2] via 10.1.1.2, 00:00:34, FastEthernet0/0
>> >
>> > C 10.1.1.0/24 is directly connected, FastEthernet0/0
>> >
>> > O IA 10.2.2.1/32 [110/1] via 10.1.1.2, 00:01:07, FastEthernet0/0
>> >
>> >
>> >
>> > I m trying to understand why the /32 are showing up. My guess would be
>> > that
>> > the point-to-multipoint non-broadcast is causing the issue but I m just
>> not
>> > sure.
>> >
>> >
>> >
>> > The second problem that I m trying to understand is why does the route
>> for
>> > 10.2.2.0/24 not appear on R1.
>> >
>> >
>> >
>> > Any insight would greatly appreciated.
>> >
>> >
>> >
>> > Thanks,
>> >
>> >
>> >
>> > Andy
>> >
>> >
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>> >
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>
>
>--
>*Narbik Kocharians
>*CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>www.MicronicsTraining.com <http://www.micronicstraining.com/>
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Received on Sat Jan 01 2000 - 01:01:01 ARST