Web Hosting Talk : Web Hosting Main Forums : Colocation and Data Centers : BGP filtering - How to avoid?

[shaggybear]

How large an IP block would I need in order to not be filtered out by other networks?

Are there considerations other than size, and objectionable traffic like spam, that are important ?

[media-hosts_com]

/24 would be the minimal...

Although, if you want to run BGP and use your ISP's ip addresses which are smaller than /24 they will most likely aggregate the advertisement into a larger block anyways.

But if you want to multihome you will need a /24.

[Spudstr]

Originally Posted by shaggybear

How large an IP block would I need in order to not be filtered out by other networks?

Are there considerations other than size, and objectionable traffic like spam, that are important ?

Filtered as in what way? As in prefix filters preventing you from announcing IP blocks that don't belong to you?

No one is going to blindly open a filter to anyone. Its the networks responsibility to maintain proper filtering on all links. Unless your a Tier1 or Tier2 network and even then on tier2 networks they still might filter you.

[shaggybear]

Hi Spudstr, that is a good point, I need to own the block in question.

http://en.wikipedia.org/wiki/Multiho...v4_multihoming says:

"Another problem to look out for is that multihoming too small a network may not be effective since route filtering is very common among BGP users and smaller prefixes may be filtered out. This will make multihoming fail."

This is why I'm asking the question.

[cooldude919]

we do this with 2 /24's out of a /22 that we have from arin and i havent seen any issues.

[Spudstr]

Originally Posted by shaggybear

Hi Spudstr, that is a good point, I need to own the block in question.

http://en.wikipedia.org/wiki/Multiho...v4_multihoming says:

"Another problem to look out for is that multihoming too small a network may not be effective since route filtering is very common among BGP users and smaller prefixes may be filtered out. This will make multihoming fail."

This is why I'm asking the question.

Everyone filters out blocks smaller than a /24. There for you need to aggretate your announcements into the biggest blocks possible. i.e a /24. As long as you have one router and not announcing a /24 here or a /22 there you can just announce the whole /20 and aggregate everything to it and be on your mary way.

[shaggybear]

Thanks guys, much appreciated!