Questions[ospf](server)

I have never worked on the customer premises, but my assumption is that one service provider runs IGP services internally - For example - OSPF or IS-IS. Now, when one service provider has to reach another service provider to communicate server on the third service provider, it will pass/transit through another ISP.

In my example - ISP-2. My question is -

Apart from multiple OSPF area's, which is to limit 50 routers per area, is it really the way internet works. You can ignore the fact that it can be IS-IS or other igp protocols within AS. In simple words, is this a kind of real topology of internet.

Next, my context based question is if this is the typical scenario, then how I can ping 11.11.11.11 from R2.

I am saying this because -

1. AS-100 has all their internal route information -- OSPF 1 -- it doesn't know how to reach 11.11.11.11

2. AS -200 has all their internal route information - OSPF 2

3. AS -300 has all their internal route information - OSPF 3

I have connected AS 100 with AS 200 using EBGP. Similarly, AS 200 with AS-300 . This I have done using neighbor command.

Questions -

Do I need to advertise each and every network information of ISP-2 to ISP1 and ISP-3 so that they all can communicate? If so, is it done in the same way in the real network. This will be such a tiring job to advertise each and every network information of ISPs. How can I do this automatically? I am using CISCO - GNS3 any cisco commands will help. I have explored re-distribute but I haven't understood much. Also, in the real network - if you advertise each and every routing information to other ISPs then the routing table will become so large. Do we normally do this? But, I believe if we don't do so then how can I communicate to internal network of other ISPs. So, I believe we have to do so. This means routing table will be very large. Am I correct here?

I have Cisco 1800 series router (running C181X-ADVIPSERVICESK9-M) with lots of IPSec tunnels. I want to add this router to OSPF and configure it to advertise routes to remote subnets accessible via IPSec tunnels (e.g. if I have tunnel VPN1 with access list that allows all traffic from my network to 10.20.30.0/24 go through that tunnel, I want router to advertise route to 10.20.30.0/24 in OSPF). Can this be achieved on Cisco IOS without explicitly adding routes to those remote subnets?

What is the difference between OSPF and RIP? Could someone explain the advantages and disadvantage？ Also when I should use one or the other.

We have 4 offices in different countries. They are all connected via VPN to each other (i.e. at least one VPN tunnel from each office to all other three). Each office has between 1 and 4 separate subnets, and each office has an OpenVPN server. Two of the offices have a DMZ (because they host public services) and each office has direct routing to the Internet. Plus there is one "virtual" office, which is physically at the same place as one of the others, but logically completely separate and connected via a VPN tunnel. In total there are 16 subnets and at the moment this is all done with static routes, complete with failover routes. There are 12 main routers involved.

It all works fine, but I am beginning to wonder whether I should look into using OSPF. Everytime I need to add a subnet, I have quite a job on hand to make sure that all the routing tables are updated correctly.

So I was wondering whether anybody could offer advice on when to start using OSPF for this?

EDIT: If anybody can provide any pointers to a good tutorial or design guide for OSPF areas, I would be greatful.

I want to setup a dynamic routing network， I want to know, What is the difference between BGP and OSPF ? Does both two need to be used together commonly ?