# BGP route Advertisement(https://networklessons.com/bgp/introduction-to-bgp)

**URL:** https://forum.networklessons.com/t/bgp-route-advertisement-https-networklessons-com-bgp-introduction-to-bgp/10637
**Category:** BGP
**Created:** [April 8, 2020, 3:49pm UTC](https://forum.networklessons.com/t/bgp-route-advertisement-https-networklessons-com-bgp-introduction-to-bgp/10637 "2020-04-08T15:49:52Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![michael3.chung](https://cdn-forum.networklessons.com/letter_avatar_proxy/v4/letter/m/ecd19e/32.png) [@michael3.chung](https://forum.networklessons.com/u/michael3.chung)
#### Post date: [April 8, 2020, 3:49pm UTC](https://forum.networklessons.com/t/bgp-route-advertisement-https-networklessons-com-bgp-introduction-to-bgp/10637/1 "2020-04-08T15:49:52Z")

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Hi  
I have some question about how many routes(network prefix) should an AS learn or advertise.

\<We can use BGP to advertise our address space to the ISPs but what are the ISPS going to advertise to our customer through BGP? There are a number of options:

They advertise only a default route.  
They advertise a default route and a partial routing table.  
They advertise the full Internet routing table.\>

q1) How many network prefixes does an AS advertise ? I mean the prefixes made by IGP intra AS.  
I guess it can be only one prefix if the AS has one aggregated network(supernet) such as 10.0.0.0/8  
q2) Are there about 500,000 bgp prefixes(full routing table) in spite of supernetting ?  
q3) Advertising method : ‘network’ command or Redistribute  
a) Why we use Redistribute?  
b) case study: OSPF table has 1,000 routes. Redistribute OSPF into BGP  
I think this redisribution does not make sense because 1,000 routes is useless. These route should be aggregated and then advertised.

Thanks  
Michael

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### Author: ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis)
#### Post date: [April 9, 2020, 5:20am UTC](https://forum.networklessons.com/t/bgp-route-advertisement-https-networklessons-com-bgp-introduction-to-bgp/10637/2 "2020-04-09T05:20:38Z")

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A post was merged into an existing topic: [Introduction to BGP](https://forum.networklessons.com/t/introduction-to-bgp/1227)

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### Author: ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis)
#### Post date: [April 9, 2020, 5:20am UTC](https://forum.networklessons.com/t/bgp-route-advertisement-https-networklessons-com-bgp-introduction-to-bgp/10637/3 "2020-04-09T05:20:38Z")

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