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Topic: Area Border Router

	Open Shortest Path First - Wikipedia, the free encyclopedia (Site not responding. Last check: 2007-10-06)
		A link state database is constructed of the network topology which is identical on all routers in the area.
		Routers in the same broadcast domain or at each end of a point to point link form adjacencies when they have discovered each other.
		All other areas are connected to it, and intra-area routing happens via a router connected to the backbone area.
	en.wikipedia.org /wiki/OSPF (728 words)

	Configuring an Area Border Router
		In Figure 5-6, for example, Border router 2 floods summaries from Area B to the backbone and Area C. Through the backbone, the summaries are forwarded to all other areas in the AS.
		If the border router has an interface to a backbone network, that router is considered to be physically connected to the backbone.
		An area that provides a virtual link between a border router and the backbone is considered to be a transit area.
	www25.nortelnetworks.com /library/tpubs/html/router/soft1100/114065A/J_59.HTM (891 words)

	RFC 3509 (rfc3509) - Alternative Implementations of OSPF Area Border Route (Site not responding. Last check: 2007-10-06)
		Though the definition of the Area Border Router (ABR) in the OSPF specification does not require a router with multiple attached areas to have a backbone connection, it is actually necessary to provide successful routing to the inter-area and external destinations.
		Area Border Router (ABR): Cisco Systems Interpretation: A router is considered to be an ABR if it has more than one area Actively Attached and one of them is the backbone area.
		For Cisco ABR approach, the algorithm for the summary-LSAs origination is changed to prevent loops of summary-LSAs in situations where the router considers itself an ABR but doesn't have an Active Backbone Connection (and, consequently, examines summaries from all attached areas).
	www.faqs.org /rfcs/rfc3509.html (2545 words)

	Network Computing \| Feature \| Network & Systems Infrastructure \| IP Routing 101: Interior Gateway Protocols \| Page 2 \| ...
		Edge areas must exchange their summary information through the backbone area, meaning OSPF imposes a mandatory two-tier hierarchy on interarea route exchanges (this applies only to the route-control messages, not to all network traffic).
		Areas have 32-bit identifiers (which are normally written as IPv4 network addresses), while the backbone area is always numbered 0.
		In OSPF lingo, a router that participates in multiple areas simultaneously is an ABR (Area Border Router), while a router that exchanges data with foreign routing protocols is known as an ASBR (Autonomous System Border Router).
	www.nwc.com /1304/1304f42.html (1216 words)

	Configuring OSPF Routing
		When an OSPF router detects a change on one of its interfaces, it modifies its topological database and multicasts the change to its adjacent neighbor, which in turn propagates the change to its adjacent neighbor until all routers within an area have synchronized topological databases.
		The administrator chooses which router is to be the designated router based on the processing power, speed, and memory of the system, and then assigns priorities to other routers on the network in case the backup designated router is also down at the same time.
		For areas that are connected to the backbone by only one ABR (that is, the area has one exit point), there is no need to maintain information about external routes.
	www.hal-pc.org /~ascend/Max/max6000/isptele/maxospf.htm (8227 words)

	Zvon - RFC 3509 [Alternative Implementations of OSPF Area Border Routers] - Overview
		According to [Ref1] a router having attachments to multiple areas is called an "area border router" (ABR).
		In OSPF domains the area topology is restricted so that there must be a backbone area (area 0) and all other areas must have either physical or virtual connections to the backbone.
		Being an ABR, R3 can only consider summary-LSAs from the backbone when building the routing table (according to section 16.2 of [Ref1]), so it will not have any inter-area routes in its routing table, but only intra-area routes from both Area 1 and Area 2.
	www.zvon.org /tmRFC/RFC3509/Output/chapter1.html (925 words)

	[No title]
		Depending upon the type of OSPF router to be used, it may be necessary to perform some additional configuration tasks.
		Specifies that the area is a stub area.
		Areas become disconnected from one another when they are not attached to the backbone and do not share a Border router.
	boulder.noaa.gov /noc/fore/lib/techpubs/docs/manuals/lan/ph50pro/phprot13.htm (5166 words)

	RFC3509: Alternative Implementations of OSPF Area Border Routers. A.... (Site not responding. Last check: 2007-10-06)
		Informational [Page 1] RFC 3509 OSPF ABR Behavior April 2003 1.2 Motivation In OSPF domains the area topology is restricted so that there must be a backbone area (area 0) and all other areas must have either physical or virtual connections to the backbone.
		Informational [Page 4] RFC 3509 OSPF ABR Behavior April 2003 2 Changes to ABR Behavior 2.1 Definitions The following definitions will be used in this document to describe the new ABR behaviors: Configured area: An area is considered configured if the router has at least one interface in any state assigned to that area.
		Informational [Page 7] RFC 3509 OSPF ABR Behavior April 2003 Note that this problem does not appear if one of the routers has a real interface in the backbone, as it usually is in real networks.
	rfc3509.x42.com (2631 words)

	Shiva(R) Integrator 150/200/500 - The area command (Site not responding. Last check: 2007-10-06)
		Areas are used to reduce the size of the database held by each router in the Autonomous System.
		This defines whether the area is a stub area or not.
		Routing information from other protocols does not enter stub areas, so the size of the OSPF link state database of routers within the area is reduced.
	www.intel.com /support/si/routers/integrator/cd0281.htm (610 words)

	[No title]
		Tutti i routers creeranno quindi le proprie adiacenze con entrambi i routers DR e BDR; se il DR cade, l'anomalia verra' immediatamente rilevata dal protocollo Hello, il BDR diventera' immediatamente DR ed un nuovo BDR verra' eletto.
		Allo scopo di connettere l'intera rete, alcuni routers appartengono a piu' aree - tipicamente a un'area a basso livello e all'area di backbone.
		Intra-area : i pacchetti vengono scambiati tra router appartenenti alla stessa area
	netgroup.polito.it /nettuno/ospf/ospf.htm (1214 words)

	OSPF Areas
		Conserving router resources – an OSPF router does NOT maintain a topology database of areas that is does not participate in.
		The ABR is a router that connects the backbone to a non-zero area.
		Alternative ABR relaxes the requirement for an ABR to be connected to the Backbone, and allows the ABR to connect two non-zero areas.
	www.riverstonenet.com /support/ospf/ospf-areas.htm (1363 words)

	Roxen Community: RFC 3509 Alternative Implementations of OSPF Area Border Routers (Informational)
		Configured area: An area is considered configured if the router has at least one interface in any state assigned to that area.
		Cisco Systems Interpretation: A router is considered to be an ABR if it has more than one area Actively Attached and one of them is the backbone area.
		The Cisco ABR approach described in this document requires an ABR to have at least one active interface in the backbone area.
	chat.roxen.com /developers/idocs/rfc/rfc3509.html (2496 words)

	Cisco - OSPF Not-So-Stubby Area (NSSA)
		It is a non-proprietary extension of the existing stub area feature that allows the injection of external routes in a limited fashion into the stub area.
		In the case of a stub area or an NSSA totally stub area, the NSSA ABR does generate a default summary route.
		By defining an area as a NSSA totally stub area, the NSSA ABR generates a default summary route.
	www.cisco.com /warp/public/104/nssa.html (1158 words)

	A.4.2 Router links advertisements
		All of the router's links to the area must be described in a single router links advertisement.
		In router links advertisements, the Link State ID field is set to the router's OSPF Router ID. The T-bit is set in the advertisement's Option field if and only if the router is able to calculate a separate set of routes for each IP TOS.
		When set, the router is an endpoint of an active virtual link that is using the described area as a Transit area (V is for virtual link endpoint).
	www.freesoft.org /CIE/RFC/1583/111.htm (694 words)

	Zvon - RFC 3509 [Alternative Implementations of OSPF Area Border Routers] - Changes to ABR Behavior
		The following definitions will be used in this document to describe the new ABR behaviors: Configured area: An area is considered configured if the router has at least one interface in any state assigned to that area.
		The algorithm for Type 1 LSA (router-LSA) origination is changed to prevent a multi-area connected router from identifying itself as an ABR by the bit B (as described in section 12.4.1 of [Ref1]) until it considers itself as an ABR according to the definitions given in section 2.1.
		So, the paragraph 2 of subsection 12.4.3 of [Ref1] should be interpreted as follows: "Summary-LSAs are originated by area border routers.
	www.zvon.org /tmRFC/RFC3509/Output/chapter2.html (691 words)

	Cisco - MPLS VPN over ATM: with OSPF on the Customer Side (with Area 0)
		The PE routers are ABR and ASBR routers.
		In this case, the CE router is an ABR because it is also connected to another area.
		If this router was only to have interfaces in area 0, it would be an ordinary router, not an ABR or ASBR.
	www.cisco.com /warp/public/121/mpls_ospf2.html (2276 words)

	BSCI Exam OSPF practice questions: OSPF area environment.
		Backbone router: Backbone routers sit on the perimeter of Area 0, with at least one interface connected to backbone (Area 0).
		Area Border Router (ABR): ABRs are routers that have interfaces attached to multiple areas.
		It may be noted that these routers maintain separate link-state databases for each area that they are connected.
	www.simulationexams.com /SampleQuestions/Routing/ospf/routing_ospf_q7.htm (235 words)

	area stub (Site not responding. Last check: 2007-10-06)
		To define an area as a stub area, use thearea stub router configuration command.
		There are two stub area router configuration commands: the stub and default-cost options of the arearouter configuration command.
		In all routers attached to the stub area, the area should be configured as a stub area using the stub option of the area command.
	web.sea.devry.edu /bwilkins/NCM-268/CD-ROM/IOS/IOS%20Config%203/5.htm (336 words)

	Network Computing \| Feature \| Network & Systems Infrastructure \| IP Routing 101: Interior Gateway Protocols \| Page 3 \| ... (Site not responding. Last check: 2007-10-06)
		When OSPF routers build their routing maps, the total cost for all the outbound interfaces in between the router and the known destinations is incorporated in the cost-vector algorithm.
		But if that link failed, Router B would send the data to Router D for forwarding to Router C, since the cumulative cost for that path would be 128, which is cheaper than using the dial-up backup line, which has a cost of 781.
		However, Router C may end up using Router B if the San Mateo RIP routing has been given a fixed-cost metric, which represents that the San Mateo network is available through a high-speed Ethernet link rather than providing explicit costs for all the networks at San Mateo separately.
	www.networkcomputing.biz /1304/1304f43.html (1186 words)

	Network Computing \| Feature \| Network & Systems Infrastructure \| IP Routing 101: Interior Gateway Protocols \| Page 1 \| ...
		Whenever a router advertises a route, it increments the known distance metric by one hop.
		Meanwhile, Router B would advertise single-hop routes for its local Ethernet attachment, a single-hop route for the WAN subnet and multihop routes for the networks in the remote areas (including the network segment that Server Z is attached to).
		With this technique, Router A may lose sight of the Server Z segment, but it would never learn of a better path through Router B. Another technique often used to prevent localized routing loops is poison reverse, which uses a hop count of 16 to explicitly corrupt the reverse path.
	www.networkcomputing.com /1304/1304f4.html (1163 words)

	[No title]
		Ci sono 5 tipi di link state o LS (router, rete, sommario per rete IP, sommario per router di confine, esterno) e 4 tipi di record link state, in quanto i sommari dei link per rete IP e per router di confine hanno lo stesso formato.
		Siccome gli LSA generati da un internal router devono raggiungere tutti i router della sua area, le reti contenute in un'area devono essere contigue, cioè deve essere possibile spostare un pacchetto da un qualsiasi router interno all'area ad un qualsiasi altro transitando esclusivamente su collegamenti (e router) interni all'area.
		I routers che non supportano il TOS routing settano il bit "support-of-TOS" a 0 nel loro LSA e, onde evitare possibili situazioni di destinazioni irraggiungibili che potrebbero verificarsi per routers non zero TOS, questi instraderanno sempre i pacchetti in accordo al TOS 0.
	netgroup.polito.it /nettuno/ospf/lsdbase.htm (1199 words)

	[nsp] Cisco 3620 - Border Router
		The memory on the 3620 is NA on a 3660 so you will have to upgrade that when you purchase the router.
		There are timers that OSPF does have that allow you to tune the database, however, care must be given that you do not unoptimize your network redundancy when you are trying to optimize CPU and limit lsas received.
		> > > > 5 areas should not be a problem depending on the amount of > memory this router is > > running and it's current processor load.
	puck.nether.net /pipermail/cisco-nsp/2002-August/000416.html (908 words)

	Basic OSPF Configuration
		The RS router (similarly to UNIX hosts) has a loobpack interface, which is always active, even though it is not configured.
		Leaving the Router ID unconfigured and therefore assigned to a physical IP interface is not advisable since physical interfaces are unstable and their IP addresses can be configurationally changed, which will cause the OSPF router to drop and recreate its neighbor adjacencies, leading to unnecessary instability.
		Riverstone Networks recommends that Router ID be always manually configured and be the same as the loopback interface.
	www.riverstonenet.com /support/ospf/basic-configuration.htm (634 words)

	Routers/Switches: Border Router Problem
		I can not ping the secondary address of my ISP's router from my new router when I place it in between the firewall and the ISP router, and no traffic makes it past the new router from the inside network.
		As Lrmoore stated, since the outside address of your firewall is on the same network as the ethernet interface as your router, it will show up as directly connected so no route is required since it already knows how to get there.
		They seem to think it is standard practice to have the same network on both sides of the router and use static routes (to the same subnet)/proxy arp to get around the havoc it causes.
	www.experts-exchange.com /Web/Hosting/Q_20456770.html (864 words)

	area border router - Industrial Partner (Site not responding. Last check: 2007-10-06)
		In OSPF, a router that attaches to the backbone and one other area.
		An area border router runs separate copies of the shortest-path-first (SPF) algorithm for each area it attaches to.
		Area border routers condense the topological information of their attached areas and distribute it over the backbone to the other areas.
	www.industrialpartner.com /definitions/area-border-router.htm (63 words)

	Mainframeforum - Mainframe as Area Border Route (Site not responding. Last check: 2007-10-06)
		We're looking at moving from CIPs functioning as ABRs between the M/F and Switch onto the network, to OSA/GbE on the M/F to the switch.
		First off, Using the mainframe as an area border router is a function of OMPROUTE and OSPF, not any one interface.
		Leave the function of Area Border Router to the router folks (Cisco, Nortel etc).
	www.mainframeforum.com /t626133.html (138 words)

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