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Webcast-Catalyst9k
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Why do ISP's not allow /24 address space advertising for companies

I'm a Junior network engineer working for a company who wants to announce our internet IP block /24 (using bgp) at two different sites to allow site redundancy. I've heard that some ISP's do not like advertising /24's. Does anyone know why this? Any help would be greatly appreciated.

3 ACCEPTED SOLUTIONS

Accepted Solutions

Why do ISP's not allow /24 address space advertising for compani

Hi Michael,

Simple answer is that it will complicate things like address aggregation at ISP end, if that address space is not be provided by same ISP.

HTH,

Smitesh

Why do ISP's not allow /24 address space advertising for compani

Hi Michael,

nowdays the local/regional ISP should accept your /24 ( doesn't metter if  PI or PA subnet ) without problem, the problem can arise at aggregation point at Tier1/2 if some of them use filter to filter the prefixes on thier length.

Why do ISP's not allow /24 address space advertising for compani

to add to the above posts

it depends if this is for the Internet or private IP range for WAN communications

if its internet then you need to have agreement with both ISP to allow you public range go via both of them

if its IP WAN then you should be able to advertise whatever you want if you use routing with the ISP like RIP or BGP for example

other than this it might a policy with some ISPs and you can discuss it with them in anyway

hope this help

if helpful Rate

4 REPLIES

Why do ISP's not allow /24 address space advertising for compani

Hi Michael,

Simple answer is that it will complicate things like address aggregation at ISP end, if that address space is not be provided by same ISP.

HTH,

Smitesh

New Member

Why do ISP's not allow /24 address space advertising for compani

thanks

Why do ISP's not allow /24 address space advertising for compani

Hi Michael,

nowdays the local/regional ISP should accept your /24 ( doesn't metter if  PI or PA subnet ) without problem, the problem can arise at aggregation point at Tier1/2 if some of them use filter to filter the prefixes on thier length.

Why do ISP's not allow /24 address space advertising for compani

to add to the above posts

it depends if this is for the Internet or private IP range for WAN communications

if its internet then you need to have agreement with both ISP to allow you public range go via both of them

if its IP WAN then you should be able to advertise whatever you want if you use routing with the ISP like RIP or BGP for example

other than this it might a policy with some ISPs and you can discuss it with them in anyway

hope this help

if helpful Rate

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