Ospf area

Hi experts..I have a bit confusion about NSSA. Stub area does not allow external routes but NSSA allow. So what is difference between configuring an area as NSSA and not configuring area as NSSA or any type of stub.
Pls make me clear.

Below link is a good explanation:
https://learningnetwork.cisco.com/docs/DOC-13814
If something is not clear, ask your question here.
HTH
Houtan

Similar Messages

Is there a single DR/BDR for the entire ospf area?

Hi guys, I was just wondering is there a single DR/BDR for an entire ospf area or does a dr/bdr election take place between every point to point Ethernet link between routers? Thanks

Hi,
It would be between every point to point Ethernet link if you don't configure ip ospf point-to-point under the interfaces.
HTH

Filtering External Type 1 routes between OSPF areas

Hello. I have a situation where I have two different telco's providing Metro Ethernet services to my site. Both providers will be sending me routes as OSPF external type 1's. I want to prevent the ISP's routers from peering with one another. One way I was thinking of accomplishing this is by making the connection to ISP1 under OSPF area 1 and to ISP2 area 2.
Is there a way I can filter the LSA's so no information is transferred between the two ISP routers in the two areas? Specifically, I don't want the type 5 LSA's generated by each ISP router to be sent to the other ISP router.
Thanks

Mike
I do not think that configuring two areas will do what you need. But I think that you could achieve this by configuring separate OSPF processes. When you have separate processes they do not share information automatically. You must redistribute routes from one process to another and you can control what routes are redistributed.
Finding the optimum solution would require more knowledge of your environment and your complete requirements than we have. But I syspect that something like this will work for you:
configure ospf 1 and put the connection from ISP 1 into it. configure ospf 2 and put the connection from ISP 2 into it. configure ospf 99 (or whatever number you like) and put the connections from your network into that process. Then you can redistribute from 1 and 2 into 99 but not redistribute between 1 and 2. And if you need to advertise your routes to the ISPs then you probably need to redistribute from 99 into 1 and 2.
HTH
Rick

No of Routers in OSPF Area

Hi,
could any one please tell me ideally how many routers should be there in a single OSPF area ?
regards
Neo

Hi,
The maximum number of routers per area depends on several factors, including the following:
What kind of area do you have?
What kind of CPU power do you have in that area?
What kind of media?
Will you be running OSPF in NBMA mode?
Is your NBMA network meshed?
Do you have a lot of external LSAs in the network?
Are other areas well summarized?
For this reason, it's difficult to specify a maximum number of routers per area. Consult your local sales or system engineer for specific network design help.
As per the Self-Study book, the optimal number of routers per area varies based on factors like network stability, but Cisco recommends no more than 50-100 routers per area.
Pls do rate all helpful posts.

OSPF Area Addition - Design Question

Hello,
I have a design question regarding OSPF. I am looking to add a new ospf area (1). The area will live on two Core routers and two Distribution routers. Can you please look at the attached Pics and tell me which design is better.
I would like to be able to connect Core-01 to Dist-01 and Core-02 to Dist-02 with a connection between Dist-01 and Dist-02, but this will result in a discontiguous area, correct?
Thanks,
Lee

I would say that the more common design is to have just backbone area links between the core routers. But there is no real issue with having an area 1 link between them...
If I were you, I would not make the area a totally NSSA. Here are my reasons for that:
- you will get sub-optimal routing out of the area since you have two ABRs and each distribution router will pick the closest one of them to get out to the backbone even though it may be more optimal to use the other one
- in an NSSA case, one of the two ABRs will be designated as the NSSA translator, which means that if you are doing summarisation on the ABRs, all traffic destined for these summarised routes will be drawn to the area through that one ABR.
Paresh

OSPF AREA 0

Hi,
I work for a company and noticed they having everything in area 0. They must have well over 350 routers in the core. As I was studying my CCNP I new there was a limitation to having some many routers in area 0. I have been told that they way this is designed is with loads of point to point interfaces so /30 so at max there is only 2 interface performing in area 0 at each time. Is this correct? is this a good OSPF design?

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As both Paul and Rick have already noted, the real advantage of OSPF areas is containing how much information a router must (internally) manage for the OSPF topology.
An old rule-of-thumb, was no more than 50 routers per OSPF area, but many variables are involved beyond just the number of routers.
Newer "routers" are often much "faster", and on Cisco devices, there's an optional incremental SPF feature which might reduce some of the CPU cycles needed to (internally) manage the topology. (NB: Cisco OSPF later OSPF implementations have other subtle ways of supporting OSPF that assist in supporting larger topologies.)
So, as Rick also noted, just knowing there's 350 routers doesn't mean it's actually a bad design.
PS:
BTW, for your /30 Ethernet links, is OSPF p2p defined on the interfaces?

Out-Of-Band Management over IPSec and OSPF Area Design

Hello,
i'm planning to implement Out of band management over OSPF over IPSec Tunnel and i have a question about the OSPF area design (please see attached figure).
As network administrator our NOC is sitting in OFFICE (OSPF Area 1). Internet access is guarenteed over our DCs (Multihomed BGP peering).
Additionally we have a second internet access at OFFICE where i want to use for IPSec Tunnel and building a OSPF neighboring to our Out-of-Band Firewall, which they too have theire own internet access.
I'm planning to declare this IPSec Tunnel as OSPF AREA 3 and AREA 4 respectively for DC1 and DC2. There are no subnet overlapping.
My Question is if I should connect both areas 3 and 4 at OFFICE to the backbone area over a virtual-link or not? Would be an disadvantage if i wont use the virtual-link?
Thx for any reply

1.The AUX port on Cisco routers is either RJ-45 or DB-25. If the AUX port is RJ-45, use a flat-satin rolled RJ-45--RJ-45 cable (part number CAB-500RJ= ), which is usually provided with every Cisco router for console connections. You also need an RJ-45 to DB-25 adapter marked "MODEM" (part number CAB-25AS-MMOD) to connect the rolled cable to the DB-25 port on the modem.
2. if your router has a DB-25 AUX port, use a straight-through DB-25Female - DB25Male RS-232 cable to connect the modem to the router.
Use this document.
http://www.cisco.com/en/US/tech/tk801/tk36/technologies_tech_note09186a0080094bbc.shtml

OSPF area plan

Dear All,
I have an existing network setup, ISP1 connecting to the MPLS cloud that connects to other branch offices. ISP2 to connect to the outside world. I only have area 50 in my network and area 0 is at ISP1 end that is the MPLS cloud.I do not have info about ISP 2 's area 0.
I would like to upgrade my network by using Nexus 5k's to connect to my servers . Also would like to run L3 between VSS Core and the N5k's.
My question is how do i plan my OSPF design and to which area do i assign the new server farm to?(N5k's to the core VSS)
Do i create a new area or use existing area 50?
Do i create a totally stub as i am trying to minimize the LSA updates.
Do i create new area 0 in my LAN network as it does not have Area 0 , but has got it only on ISP1's MPLS cloud.
Or else is there a new plan?
Please note that all my static routes from other branches in the MPLS cloud are redistributed into OSPF as this is the hub site and all the spokes will have to go through this Core VSS to reach outside.
I am attaching the topology for reference.
B1,B2,B3 are the branches where the MPLS clouds connect to.
Thanks in advance

If you are peering with ISP1 using OSPF which it sounds like you are then you definitely don't want to create another area 0 in your LAN.
And if you created a new area that area also would need connectivity to area 0 and not via area 50 unless you configured a virtual link between area 50 and your ISP router
However in general you should only use virtual links when you have to and the ISP would have to get involved if you wanted to configure it. So I would recommend against that as it complicates things significantly with very little gain.
All you are really doing is connecting a pair of switches to your existing infrastructure and i can't really see the need to do anything other than add them to your existing area.
I understand what you mean about the switches receiving all the LSAs for remote sites but i wouldn't have thought that would be a problem for Nexus switches.
If it really was a concern then you say you are proposing to connect the switches with L3 to the VSS switches. If that was the case you could always configure routed ports with IPs and if needed configure default routes on the Nexus switches pointing to the VSS switches and configure static routes for the server subnets on the VSS switches pointing to the Nexus switches.
Whichever you use i would make it as simple as possible so definitely no need for another area as far as i can see.
Jon

OSPF areas

Can anyone tell me why we have areas in ospf, and what routes do ABR,s exchange, its it about all routes in that area ?

Hi carl_townshend
Actually we use OSPF in a very large network (many routers) . OSPF is just used to divide the whole network to number of areas (we configure some routers in one area and some on different and so on). So if their is some network failure, the whole topology does not change but only the area in which that network fails suffer.
The Area Hierarchy is as follows for your info. there is one backbone (i.e. Area 0) and all the rest areas are connected to the backbone area.
The Router that connect the backbone and other area is ABR. and ABR exchange network of one area to another, but if you can configure to route summarized network (Interarea summarization) on ABR. to reduce routing table size.

Why in ospf , area 0 is made as back bone area ,

Hi all
i have a doubt regarding area 0 which is known to be backbone area and all other areas attached to backbone area by an ABR . Why can we make any other areas as backbone say area 1 is made as backbone and all other areas connected to this area 1 via an ABR . Why its not possible , why its made as a not possible topology ? Please let me know whats the reason for this . or is it possible

Hi,
The need for a backbone area (ignoring its specific number at this point) in OSPF is given by the requirement to provide loop-free routing between areas. Inside an area, OSPF operates on a link-state basis and uses the Dijkstra algorithm to compute the shortest paths. The Dijkstra algorithm by itself never causes a routing loop, and so the loop-free routing inside an area is guaranteed. However, between areas, OSPF resorts to distance-vector routing which is prone to transient routing loops. Therefore, to prevent routing loops in inter-area routing, OSPF by its internal design mandates and imposes a logical star topology between areas: the center of the star is the backbone area, the spokes are the non-backbone areas. Even if you configure a physical link between non-backbone areas, OSPF will not use it. As a result, the logical topology of areas in OSPF is always a loop-free star topology with the backbone area in the center and all other areas attaching to the backbone.
Notice that there cannot be multiple backbone areas as a star cannot have multiple centers.
Now because only a single area can ever act as a backbone area, OSPF designers decided that this area will be assigned the number 0 from beginning and that this number will not be configurable. In theory, they could adopt your approach: decide which single area is going to be a backbone, and then configure the routers to know that it really is the backbone. However, notice that this approach only adds to the complexity of the configuration and does not bring you any added flexibility: only a single area can ever be a backbone, and if the backbone area number was configurable, you would have an additional burden of configuring all routers with the information what area number should be interpreted as the backbone area ID. Simply put, there would be no added value in this: The backbone area would still be only a single area, and you would in addition need to configure extra commands to tell routers who the backbone area is. With the established rule in OSPF that the backbone area is always the area ID 0, the life is simpler :)
Best regards,
Peter

Multi-areas in OSPF routing questions

Hi Guys,
I currently have 2 x L3 switches, one is for area 0 and the other one is for area 5 and they're connected to each other. Since there are only 2 VLANs on each switch, I'd like to replace both of them with a better switch but unsure about the areas routing on the same L3 switch. Please let me know what your thoughts are.
Switch A is connected to switch B thru interface g1/0/1 with ip address: 10.10.10.1/26
I'm currently using ospf and here is the configure of switch A:
router ospf 1
network 172.20.1.1 0.0.0.0 area 0
network 172.21.1.1 0.0.0.0 area 0
network 10.10.10.1 0.0.0.0 area 5
And this is OSPF routing configure of switch B:
router ospf 1
network 192.168.1.1 0.0.0.0 area 5
network 10.10.10.2 0.0.0.0 area 5
I'd assume the new switch C is the replacement of switch A & B. And here is my routing configuration of switch C:
router ospf 1
network 172.20.1.1 0.0.0.0 area 0
network 172.21.1.1 0.0.0.0 area 0
network 10.10.10.1 0.0.0.0 area 0
network 192.168.1.1 0.0.0.0 area 5
network 10.10.10.2 0.0.0.0 area 5
Is this going to work and/or best cisco practices? if not please advise. Thanks.

Hi,
Since you are replacing 2 switches with 1, now you don't need the transit subnet (10.10.10.1/26) between the 2 switches any more. What will the new switch connect to? Is the new switch going to peer with any other device? If it is a stand alone switch, why do you even need 2 OSPF areas or even need OSPF all together?
HTH

Are this OSPF LSA relate to each other ???

OSPF neighbor relationships progress
1) Down State
2) Init State
OSPF routers send Type 1 (hello)
3) Two-Way State
4) ExStart State (Type 2)
5) Exchange State
6) Loading State (type 3)
7) Full Adjacency
ALSO,
OSPF Area Types also use LSA exchange between routers or area
Type 1 generate by each router for each area it belongs to, flood only within particular area, describe the states of the routers link to the area.
Type 2 generate by DR in multi-access networks, flood only within the area that contain the network, describe the set of routes attched to a particular network.
Type 3 Orgin by ABR, flood throughout the backbone area to other ABRs, describe the links between ABR and the internal routes of a local area.
Type 4 Orgin by ABR, flood throughout the backbone area to other ABRs, describe routes to ASBRs.
Type 5 Orgin by ASBR, describe the routes to destinations external to the AS, flood throughout an OSPF AS.
The questions are this LSA relate to each other or it just happen like this ???

Hi Friend,
There is no relation between the type of LSA (1,2,3,4,5,7) exchanged between the routers within an area and between the areas to exchange the link state information and the packets which are used to form an ospf neigh and adjancy relationship.
Taking an example LSA 5 which is used to carry the external route information into an area is not at all related to type 5 LSA which you are talking for formaing a naighbor relationship.
I think the neighbor relationship is formed using hello packet, dd packet and LSU and LSR packets which you may name as type of LSA's. but these are not at all related to LSA's which are used to carry route information between the areas and within areas.
HTH
Ankur

Hi all, need advice on OSPF and private vlans

Hi all.
I have a project to complete and need some help on the possible solution I can use.
Basically we have ospf area 0 and the users in question are in ospf area 7 and is a stub.
I need to route the traffic from these users out through area 0 through 3 core devices, onto an external firewall interface to be placed onto the vpn that sits on it. The firewall is not included in the ospf domain.
My thinking was that the firewall has a default route back into the ospf domain so dont need to worry about traffic coming in, however my job is to segregate these users and take them out of our core network and place them onto an external network via this vpn.
Not sure how to achieve this apart from static routing redistributed but surely this does not seperate their traffic only points the route to ospf?!
I was thinking I might have to use private vlans or policy routing but when I try policy routing the policy gets ignored due to normal forwarding.
Any help and advice would be greatly appreciated.
Cheers
Steve

Steve
Thanks, that helps.
GRE is defintely out because apart from the 6500 GRE tunneling is not supported on the Cisco switches.
It's good that area 7 is only for these users and not mixed up with other users.
So if i understand correcty the 4500 interface connecting to the 6500 is in area 0 and the interface connecting to the 3550 is in area.
Or is the 3550 connected to both areas and the 4500 totally in area 0 ?
Can you confirm the above ?
In terms of keeping them separate there are 2 possible choices. You can either -
1) use VRF-LIte, although i'm not sure whether the HP switch would support this. With VRF-Lite you are in effect creating virtual devices on the same physical device. This means each virtual device has it's own routing and forwarding table so it is quite secure because you would only populate the routing table with the routes needed so there would be no way for users to jump to thes rest of your networks.
The downside is that is can become quite complex to configure. If the 4500 is only used to connect are 7 to area 0 then that would not be a problem but the connection from the 6500 to the HP could and i don't even know whether the HP supports VRF-Lite functionality let alone how to configure it on that switch.
But it would, at least from the 4500 to 6500 to HP provide complete separation in terms of routing and forwarding. Once it got to the HP it wouldn't but that might not be an issue.
2) Use PBR (possibly together with acls). This is easier to configure ie. you configure PBR on the 4500 and the 6500 to get the traffic to the HP switch. But you do not get the actual separation you get with VRF-Lite ie. the traffic simply overrides the existing routing tables.
The other thing to bear in mind with PBR is that you also have to configure the return traffic as well so each device would need multiple PBR configs.
Again i don't know whether the HP supports PBR but it may not be an issue depending on what the routing is on the HP.
You could also use a combination of the above ie VRF-Lite between the Cisco switches and then PBR for the last hop to the HP device.
I should say i don't have a huge amount of experience with VRF-Lite but that should not necessarily stop you using it if it is what you need. There are lots of other people on here so i'm sure there will be other people who can help if i can't.
It still depends on how much separation is required. VRF-Lite is definitely seen as a way to separate traffic running across a shared infrastructure, PBR is not really seen in the same way. So it may well be worth going back to find out exactly what "segregating" user traffic means.
I don't want to confuse the issue but it's still not entirely clear what the actual requirement is.
Jon

GRE over DSL with OSPF in an MPLS network

Hi guys,
we run 2 GRE tunnels in our network. The A end is a PE router while the B end are 2 different CPE DSL sites.
Both tunnels at the A end (PE) are using as a source a gig sub inteface which is in the same VRF
interface Tunnel40 (for branch office 1)
ip vrf forwarding example
ip address x.x.x.250 255.255.255.252
ip mtu 1476
ip tcp adjust-mss 1420
ip ospf dead-interval 60
ip ospf mtu-ignore
keepalive 10 6
tunnel source Gig x/x.z
tunnel destination x.x.x.x.
tunnel vrf example
interface Tunnel60 (for branch office 2)
the frame is as above
router ospf 1 vrf example
log-adjacency-changes
capability vrf-lite
passive-interface default
no passive-interface Tunnel40
no passive-interface Tunnel60
network x.x.x.250 0.0.0.0 area x.x.x.x
.network ......
CPE example
interface Tunnel1
ip address x.x.x.249 255.255.255.252
ip flow ingress
ip flow egress
ip ospf dead-interval 60
ip ospf mtu-ignore
keepalive 10 6
tunnel source Dialer1
tunnel destination z.z.z.1 ( this is the subinterafce Gig x/x.z on the PE router)
router ospf 1
router-id x.x.x.x
log-adjacency-changes
passive-interface default
no passive-interface Tunnel1
no passive-interface Vlan1
network x.x.x.x 0.0.0.0 area x.x.x.x
network x.x.x.249 0.0.0.0 area x.x.x.x
same is the config for CPE 2 ( just the frame of the commands no the ospf areas , IP s etc)
The problem is that when the tunnel fails for cpe 1 then it fails for CPE 2 exactly the same time.
Any advice.
Thanks

Hi my friend,
I didnt know about that command and the purpose you use that but I was searching a bit. Do you use that command for
normal GRE tunnels? This is not a point to multipoint topology and every tunnel is a point to point and I run ospf for the point to point link is is differnet area than the other tunnel. Do you beleive that its still could be related to the tunnel key?
Many thanks fo ryour advice. Please reply at your erliest convenience
I know it looks like hub and spoke or point to miltipoint but does it actually dehave like that?
Thank,
Spyros

Network Down for OSPF ????

Hi
My Network is as follows: Head office Connect to Brach Via Firewall to Firewall IPSEc VPN and Head office Router to Branch office router OSPF. Firewall and Router also OSPF. all the network are Layer 2 Connectivity.
Suddenly SOme days Ago one of my Core Router which are VRRP with Another Core Router. After That All the Branch are not up with the core Router where mentioned OSPF data base is update. after Static Router then Branch are Connected. Among 114 Branch 40 Branch are Up take time 4 Hours and 15 Branch manualy static connected. Now all branches are by two Core Router ( Repalce down Router)
The Router which is not down is not Responding at all in console.
My Question IS: This is any problem OSPF Table update 2. For Layer 2 , broadcast streeming and OSPF database full ? 3. VRRP is trouble ?
My ospf area just single for 114 Branch.
Regards
Iqbal

This includes all of
New England, apparently, as well as many other
states.
No it doesn't. My Edge service has been faster then it's ever been so far. CT works great.
Thanks for the update with billing though, that should be helpful for a lot of people who are experiencing a similar problem to you.

Ospf area

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