difference between interior and exterior gateway protocols

[aprocfu]

Hi, my question is about the difference between interior and exterior gateway protocols. So is it safe to say that RIP2, EIGRP, OSPF, AND ISIS are for interior gateway management which means to manage routers in different geographical area but managed by the same company. And that BGP is for exterior gateway protocol which means to manage the internet.

Thanks

 

[Minue]

Yes!!That's more ore less correct.Another way of explaining it is IGP's are use to route within an AS and BGP is use to between AS.
Your'e company "A" running OSPF and I am company "B" running EIGRP.How can I let you know about my routes to my

http://WWW,FTP

servers?Do route distribution or run the same protocol with same routing proccess.NO!!!! I use BGP.
This is a basic idea,but in the real world it's a bit more behind how it really works.
Regards

 

[burtsbees]

IS-IS can be considered to be both, though...

Burt

 

[aprocfu]

Thanks for the reply. I would like to know then if a company codes its own interior gateways, who codes for the exterior gateways?

Thanks

 

[Minue]

Hello
As I said it's more it than is normally explained.Here the picture:You company "A" has your internal network,you can use any IGP of your choice.As said before you want people to know about your website or online ordering service etc.(Note this case is for a company that want's to host their own services.)So you get a block of public ip addresses and an registered "AS" from the "powers that be".
You then ask your ISP to become BGP peer with you.Your address block and "AS" is then pass on to the rest of the world.As for your inside network setup,your router will be running OSPF or EIGRP and redistributing your public ip address into BGP.
The big companies use this method but there are other method for small companies can use.
For any more question feel free to ask.

Regards

 

[jneiberger]

As for who configures the routing, that completely depends on the organization. One company might have an employee configure the interior stuff (IS-IS, OSPF, EIGRP, etc.) and have a consultant configure the exterior stuff (BGP). Other have consultants configure the whole thing. I was lucky enough to work somewhere where I was in control of both the interior and exterior stuff.

To simplify the terms, interior protocols are for maintaining a consistent topology within an autonomous system. Very fast convergence is usually a design goal.

BGP (the only exterior protocol in use on the Internet) has different design goals. Very fast convergence isn't as important as enforcing policy and maintaining order and consistency on the Internet. The hardest thing to learn about BGP is what you're trying to accomplish in the first place. You need to understand routing policy on the Internet. You have to know quite a bit about it before you ever attempt to configure it.

 

[Belushi]

BGP is both used internally and externally. Many, many companies use BGP internally in conjunction with their IGPs. Examples include:

1. BGP is the best protocol to redistribute between IGPs (OSPF/EIGRP/RIP/etc.)
2. BGP can handle many more routes than IGPs.
3. BGP can be tuned to converge quickly like IGPs.
4. BGP must be used (variation called MP-IBGP) to run your own MPLS VPNs internally.
5. BGP is often used to peer with a service proivder handling MPLS VPNs on your behalf.
6. Possibly the best reason, the criteria for making routing decisions is much more granular than what you'll get with an IGP.

That being said, I regularly use EIGRP, OSPF, static routing, policy based routing, Multicast routing, and yes BGP.

 

[Minue]

Hi Belushi
I have already scared "aprocf" off this post.You will make him go crazy with these advance concept ;-))

Regards

 

[aprocfu]

Thanks all you guys, including Belushi who is true has shaken me a little. I have taken a CISCO Router course in a short period where what was emphisised was only the coding part, and I did not have prior experience in networking. So I had big holes in the concept after the course ended. But with your help guys I am closing in those holes.

And this is another question I have. I know the router can have different number of ports and different kind of ports. Is it safe to say that on the same router I can code some ports for interior gateway and one port for exterior gateway. And if so is there a preference of the type of ports (serial, ethernet and so on) to assign to interior gateways and exterior gateways.

Thanks again

 

[jneiberger]

There is no preference, exactly. You can configure whatever you want on whatever interface you want. It just depends on what you need the router to do and what it's connected to. How you configure it is up to you. You configure whichever protocol on whichever interface is appropriate for the situation.

 

[Belushi]

Not only that, you can configure multiple protocols on the same ports.

 

[jneiberger]

Yep, exactly. The configuration can get really complex if you need it to be. It just depends on what you need the router to do. A very common configuration is eBGP (external) on an external interface, iBGP (internal) on an internal face for sharing BGP-learned information, and an IGP like OSPF or IS-IS on the same internal interface to handle internal routing information.

 

[Minue]

Hello
This is the way I see it.If the question is related to the former topic.You will have normally a serial interface as your WAN.(Can change because of a heavy use of new protocols like Metro Intenet and SHDSL).So you would peer with your BGP neighbor here.Ethernet is normally use to interconnect devices on the same site.So IGP would be run here.
What's important to understand is that serial interface to connect to your remote branch offices using frame relay or T1/fracional.In this case you will use a IGP.But the moment you want to use BGP,you use it on the interface that connects to your ISP.
Feel free to ask any question or clarify any doubts.
Regards

 

[aprocfu]

Thanks, I am getting out of the cloud of CISCO Routers because of your tips. I think this time my questions would be getting more specific because I see somehow the big picture. So my question is if I have a router where one port connects to the Internet, I should write a code saying route all IP address to the port configured for the Internet except those I IPs I use for interior gateway?

Sory if I cannot several questions together because I might need answer to another question.

Thanks as usual

 

[jneiberger]

Yes, that's basically the idea. More specifically, you'd use an IGP to let your routers dynamically handle your internal traffic then you could (and probably would) just have a default route pointing to the Internet.

 

[Minue]

Always following the concept of big Companies.(Note: as I said before for small companies things are a bit different).You would write a code telling BGP to advertise your public address block to world. Then you will have your public Servers address with the same addresses that BGP is announcing.Then with the IGP protocol you will write another code telling BGP of those addresses this is done with "route redistribution "( making two different protocols talk to each other)Note,that the BGP router will be running,also the IGP that you are using on your inside routers).
So your IGP route's to your "IGP/BGP" router and then BGP route's to other autonomous systems.
Regards
ps I hope I was clear,if you don't understand I will try to re-word it for you

 

[aprocfu]

Hey guys, frankly, I learned much more than I would if I delved into 3-4 books. I am going somewhere, but I wanted to thank you at least. I will be posting other questions soon.

Thanks