Why do ISP's use BGP.
Hi
Can some one tell me why do ISP's use BGP. Do they have to have Autonomous System number and BGP running on their routers. If yes then what purpose does it serve. Can an ISP not use a default route to its core connection instead of learning 90,000 routes.
Can some one tell me why do ISP's use BGP. Do they have to have Autonomous System number and BGP running on their routers. If yes then what purpose does it serve. Can an ISP not use a default route to its core connection instead of learning 90,000 routes.
ASKER
Is it not sufficient to peer with one isp and use a default route to that isp. Why would I want to peer up with more than one isp, does it matter if they are in different countries after all wer are all on the internet. Sorry for being so dum but I really need to understand the concept of internet.
Tell me if this is true, because this is what i understand of ISP. When some one registers with them they allocate the client with a static/dynamic public IP address with which the client can communicate with the rest of the internet. For the client to browse the internet they use the isp's ip as gateway and isp's dns as their forward lookup dns. On the other hand`when some one tries to contact the client from internet they must to client via its public ip address which is advertise by the isp's router using bgp.
If what ever I said is all nonsense then please tell me how the two way communication works, I can understand the default route used to go out but how does some one contact from outside to inside .
Tell me if this is true, because this is what i understand of ISP. When some one registers with them they allocate the client with a static/dynamic public IP address with which the client can communicate with the rest of the internet. For the client to browse the internet they use the isp's ip as gateway and isp's dns as their forward lookup dns. On the other hand`when some one tries to contact the client from internet they must to client via its public ip address which is advertise by the isp's router using bgp.
If what ever I said is all nonsense then please tell me how the two way communication works, I can understand the default route used to go out but how does some one contact from outside to inside .
BGP is designed to efficiently manage a large, multi-organisation routing table, such as the global Internet routing table. This provides the level of control to manage a heterogeneous environment where there is no single organisation managing all parts of the network (it's a network of autonomous systems).
None of the interior routing protocols were designed to perform this task nor can they efficiently manage the large number of routes on the Internet. RIP (and other interior routing protocols) will send out updates listing all the networks it knows about every few minutes (depending on protocol). This consumes valuable bandwidth.
BGP uses TCP as a reliable transport medium and so it needs only to send out updates when necessary rather than continuously. BGP also has many features to manage routing announcements which are not needed in an interior routing protocol.
BGP is an exterior routing protocol and as such is concerned with routing between networks rather than within them (this is the domain of the interior routing protocols such as RIP, OSPF, IS-IS).
Simply defined, BGP enables groups of routers or autonomous systems to share routing information in order to establish efficient, loop-free routes.
In order to use BGP you must have a globally unique Autonomous System Number (ASN). The number uniquely identifies the networks originated by you. An ASN can be obtained from the Asia Pacific Network Information Center using their form. Note you must be a member of the APNIC to use this service. If you are not a member of the APNIC (and do not wish to join just to get an ASN) Connect can arrange to obtain one on your behalf (for a fee). Contact your account manager for details.
The protocol is further defined in RFC1771:
http://www.cse.ohio-state.edu/cgi-bin/rfc/rfc1771.html
Othre info regarding BGP:
http://info.connect.com.au/docs/routing/general/multi-faq.shtml#moreinfo
None of the interior routing protocols were designed to perform this task nor can they efficiently manage the large number of routes on the Internet. RIP (and other interior routing protocols) will send out updates listing all the networks it knows about every few minutes (depending on protocol). This consumes valuable bandwidth.
BGP uses TCP as a reliable transport medium and so it needs only to send out updates when necessary rather than continuously. BGP also has many features to manage routing announcements which are not needed in an interior routing protocol.
BGP is an exterior routing protocol and as such is concerned with routing between networks rather than within them (this is the domain of the interior routing protocols such as RIP, OSPF, IS-IS).
Simply defined, BGP enables groups of routers or autonomous systems to share routing information in order to establish efficient, loop-free routes.
In order to use BGP you must have a globally unique Autonomous System Number (ASN). The number uniquely identifies the networks originated by you. An ASN can be obtained from the Asia Pacific Network Information Center using their form. Note you must be a member of the APNIC to use this service. If you are not a member of the APNIC (and do not wish to join just to get an ASN) Connect can arrange to obtain one on your behalf (for a fee). Contact your account manager for details.
The protocol is further defined in RFC1771:
http://www.cse.ohio-state.edu/cgi-bin/rfc/rfc1771.html
Othre info regarding BGP:
http://info.connect.com.au/docs/routing/general/multi-faq.shtml#moreinfo
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And a single ISP may 'peer' with many other ISP's, especially at places like public internet exchanges such as PAIX, LINX or HKIX. Or with different providers for redundancy.
I would want to received full routing tables, because I may peer with different ASes in different parts of the world and I can better manage my traffic.
This can be done with many of the various attributes that are available when you use BGP. It gives you very granular control over how your traffic flows, in ways that no IGP can. You can tag routes with communities, local pref, meds, and use those to filter your routing advertisements, based on performance or perhaps cost. i.e. I see a slightly better route to AS1 through my peering session with AS701, but AS7012 charges less, or perhaps I have settlement-free peering arrangements with someone else who will transit that traffic for me for free.
It's a big subject...