mohammedmahmoud Tue, 06/19/2007 - 01:34
User Badges:
  • Green, 3000 points or more

Hi,


There is no defined number, it can range from a couple of routes up to 500 routes and may be more, kindly elaborate around the reason of this question in order to help you better.



HTH,

Mohammed Mahmoud.

b.sams Wed, 06/20/2007 - 07:06
User Badges:

study for the ccna we must learn about interior routing protocols which can only be used within one AS. But when i study i design lab that doesnt really include to many routes. I would like to understand what a "typical" interior AS would like.

mohammedmahmoud Wed, 06/20/2007 - 13:32
User Badges:
  • Green, 3000 points or more

Hi,


Autonomous system (AS): a set of routers that are having a single routing policy and are running by a single technical administration.


A typical AS can start from a couple of routes upto 500 and maybe more routes.


One of the best definitions of an Autonomous System can be found in an IETF document, RFC 4271 that describes BGPv4:


"The classic definition of an Autonomous System is a set of routers under a single technical administration, using an interior gateway protocol (IGP) and common metrics to determine how to route packets within the AS, and using an inter-AS routing protocol to determine how to route packets to other ASs. Since this classic definition was developed, it has become common for a single AS to use several IGPs and sometimes several sets of metrics within an AS. The use of the term Autonomous System here stresses the fact that, even when multiple IGPs and metrics are used, the administration of an AS appears to other ASs to have a single coherent interior routing plan and presents a consistent picture of what destinations are reachable through it."



HTH,

Mohammed Mahmoud.

mheusing Thu, 06/21/2007 - 01:46
User Badges:
  • Cisco Employee,

Hi,


If your question is about the "size", i.e. number of routes of a typical IGP, there is no definate number to answer your question.

Generally speaking scalability of routing protocols depend on the protocol architecture and on the hardware ressources available (CPU, memory, bandwidth, number of interfaces, etc.). What I mean with protocol architecture is f.e. OSPF requires more memory and CPU ressources than RIP just because of the way it internally operates.

If you use an old 2500 router with only 8 MB memory it can only handle a few routes f.e. in RIP. If you take a CRS-1, a GSR or a Cat6500 with several hundred MB or even some GB of memory and considerably faster CPU(s) it might scale up to tens of thousands of routes with an IGP like OSPF. If you would have unlimited CPU, memory, bandwidth and so on, you could theoretically have as many IGP routes as you want.


There are networks with less than 100 routes and large SP or Enterprise IGPs with several thousand routes. The latter will typically use OSPF or ISIS.

Your home network will typically have less then 10 routes. As there are milions of home networks and only thousands of Enterprise/SP networks, a simple average would be less than 10. Finally you will have to deal with the specific network you are responsible for and will need to learn the odds and ends there.


So bottom line, what I would recommend to remember: IGP scalability depends on availabe ressources and on IGP protocol architecture.


Good luck for your CCNA!


Hope this helps!


Regards, Martin

b.sams Thu, 06/21/2007 - 14:04
User Badges:

thank u for your responses , they are being a great help but i am still unclear on a couple of issues if u could be so patient with me. Since i am studing for my CCNA i dont know to much about the world outside of the interior AS. BUt am i right in beliving that BGP allows interior Routing protocol to be routed thru it, i used thru for lac of a better word. BUt is that one of the gernal concepts of BGP. this is the only thing that i am not tottaly clear with


anyway thank u for time

brian

b.sams Thu, 06/21/2007 - 14:07
User Badges:

thank u for your responses , they are being a great help but i am still unclear on a couple of issues if u could be so patient with me. Since i am studing for my CCNA i dont know to much about the world outside of the interior AS. But am i right in beliving that BGP allows interior Routing protocol to be routed thru it, i used thru for lack of a better word. But is that one of the gernal concepts of BGP. This is the only thing that i am not tottaly clear with


anyway thank u for time

brian

nikhil.engineer Thu, 06/21/2007 - 17:37
User Badges:

Hi Brian,


BGP is a exterior gateway protocol.It is used in between different AS. AS is group of routers which are under single administration. BGP is divided in two parts ebgp and ibgp.

ebgp:when bgp is in between two different AS it is called ebgp

ibgp:when bgp is between same AS it is called ibgp.

To make ibgp work we require IGP.

To learn more about BGP go through below link:

http://cisco.com/en/US/tech/tk365/tk80/tsd_technology_support_sub-protocol_home.html


hope this helps

Cheers,

Nikhil

mohammedmahmoud Thu, 06/21/2007 - 23:02
User Badges:
  • Green, 3000 points or more

Hi Brian,


You are very welcomed, and we are here just to help posters resolve their issues, thus we are all very patient here for your questions.


A single AS runs an IGP (Interior Gateway Protocol),ex: RIP,EIGRP and OSPF, within its domain (between its interior router - Intra-AS routing), in the moment that AS needs to talk to the outside world (other ASs, meaning inter-AS routing) thus this AS needs to run an EGP (Exterior Gateway Protocol) with the outside world (outside ASs) the most commonly used EGP these days is BGP (actually there was another protocol called EGP but it is no more used), ok now a gateway router for our local AS will be responsible to run BGP with external ASs to do the Inter-AS routing (this router has already learned all the internal routes since it is running IGP with all the interior routers, and it can optional send what ever routes needs to be reachable to exterior ASs, and imports external routes to the local AS).


I hope that i've been informative, if you want to elaborate further on BGP the link provided by the previous poster is very useful, but i think that you should complete your CCNA first before sailing into this sea.


I really do wish you good luck in your exam :)



HTH, please do rate all helpful replies,

Mohammed Mahmoud.


Actions

This Discussion