From: Ahmed (ahmed_mustafa01@excite.com)
Date: Tue Dec 02 2003 - 17:27:59 GMT-3
Brian, Thanks for the wonderful explanation with the example. Now It makes a perfect sense to me. Regards, Ahmed--- On Mon 12/01, Brian Dennis < bdennis@internetworkexpert.com > wrote:From: Brian Dennis [mailto: bdennis@internetworkexpert.com]To: ahmed_mustafa01@excite.com, ccielab@groupstudy.comDate: Mon, 1 Dec 2003 11:33:33 -0800Subject: RE: Point-to-Multipoint non-broadcast commandOSPF point-to-multipoint non-broadcast will allow you to assign thecost on a per neighbor basis as opposed to using the interface's cost. Thisis useful on a multipoint Frame Relay interface where there are twoneighbors advertising the same route but the CIRs for the DLCIs to reacheach neighbor is different. Or these two neighbors that are advertising thesame route have different port speeds to the Frame Relay network. Rememberthat the cost is based on your incoming interface's bandwidth and not thebandwidth of the neighbor's interface that connects to you. Say we have two remote routers !
over Frame Relay and the remoterouters are both connected to and advertising the same Ethernet segment.Our router is connected to these two routers via Frame Relay. One of theremote routers has a T1 Frame Relay connection and the other has a 64k FrameRelay connection. Since our cost to the Ethernet segment advertised bythese two routers will be calculated based on the cost of the Ethernetsegment plus the cost of our incoming interface, both routes appear to beequal cost. Obviously this is not what we would want. We would want toprefer the route from the router with the T1 connection over the 64kconnection.Here is an example with two remote routers advertising the same network(loopback interfaces):Rack2R4#show ip ospf interface s0/0 | include CostProcess ID 1, Router ID 150.1.4.4, Network Type POINT_TO_MULTIPOINT, Cost:64Rack1R4#sho run int s0/0interface Serial0/0ip address 154.1.0.4 255.255.255.0encapsulation frame-relayip ospf network point-to-multipointframe-relay map ip !
154.1.0.3 403 broadcast frame-relay map ip 154.1.0.5 405 broad!
cast no
frame-relay inverse-arp endRack2R4#sho ip route 150.1.0.0 255.255.255.0 Routing entry for 150.1.0.0/24Known via "ospf 1", distance 110, metric 65, type intra areaLast update from 154.1.0.3 on Serial0/0, 00:00:30 agoRouting Descriptor Blocks:* 154.1.0.3, from 150.1.3.3, 00:00:30 ago, via Serial0/0Route metric is 65, traffic share count is 1154.1.0.5, from 150.1.5.5, 00:00:30 ago, via Serial0/0Route metric is 65, traffic share count is 1Rack2R4#As you can see both 154.1.0.3 (router-ID 150.1.3.3) and 154.1.0.5(router-ID 150.1.5.5) are advertising the 150.1.0.0/24 network with an OSPFcost of 1 (total cost minus our interface's cost, 65-64=1). If both ofthese routers have the same port speed to the Frame Relay network then thisis what we would want to see, two equal cost paths. But if they havedifferent port speeds, then we would want to prefer the route from therouter with the higher port speed, theoretically. The problem is that OSPFdoes not take into account the cost of the re!
mote router's interface to us.We only take into account the cost of the loopback and our interface's costto reach the remote neighbor.To prefer the route from the router with the higher port speed, weare going to use OSPF point-to-multipoint non-broadcast to specify the coston a per neighbor basis. In this example we are going to add a cost of 25to the routes from 154.1.0.5 and 50 to the routes from 154.1.0.3.Rack1R4#sho run | be router ospfrouter ospf 1network 154.1.0.0 0.0.255.255 area 0neighbor 154.1.0.5 cost 25neighbor 154.1.0.3 cost 50Rack1R4#sho run int s0/0interface Serial0/0ip address 154.1.0.4 255.255.255.0encapsulation frame-relayip ospf network point-to-multipoint non-broadcast frame-relay map ip 154.1.0.3 403 broadcast frame-relay map ip 154.1.0.5 405 broadcast no frame-relay inverse-arp endRack1R4#sho ip route 150.1.0.0 255.255.255.0 Routing entry for 150.1.0.0/24Known via "ospf 1", distance 110, metric 26, type intra areaLast update from 154.1.0.5 on Serial0/0!
, 00:06:13 agoRouting Descriptor Blocks:* 154.1.0.5, from 150.!
1.5.5, 0
0:
06:13 ago, via Serial0/0Route metric is 26, traffic share count is 1^^^^^^^^^^^^^^^^^^^Now we can see that we prefer the route from 154.1.0.5 (router-ID150.1.5.5).Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)bdennis@internetworkexpert.com Toll Free: 877-224-8987Direct: 775-745-6404 (Outside the US and Canada)Internetwork Expert, Inc.http://www.InternetworkExpert.com-----Original Message-----From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf OfAhmedSent: Saturday, November 29, 2003 7:40 PMTo: ccielab@groupstudy.comSubject: Point-to-Multipoint non-broadcast commandWhat is the reason for the command "POINT-TO-MULTIPOINT NON-BROADCAST" inan OSPF over Frame-Relay environment? I read the document on CCO, but wasnot very clear. Can someone please explain it with the example? Thanks,Ahmed_______________________________________________Join Excite! - http://www.excite.comThe most personalized portal on the Web!_________________________________________________!
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