BGP Question - CIDR /24

[rsommer]

We are thinking about using our public addresses - a class C. New to this, but after some reading, I have some concerns. We will advertise /24 - which our ISP will forward. I read that many BGP peers filter out the /24's to reduce routing overhead. This may introduce latency as peer defaults will be used until the route is found. True?

[Richard Burts]

Will you be connecting to a single ISP or multiple ISPs? (If connecting to a single ISP there may be options that would work for you that are less complex than running BGP.)

Is your class C address space part of your providers address space - and will they advertise your unique /24 or will they summarize your addresses into part of a larger block?

Considering answers to these questions may clarify your approach to routing with your ISP>

HTH

Rick

[rsommer]

Eventually be multihomed - but right now to a single ISP. Since we own that Class C (not a part of the ISP's space) - I don't BELIEVE they will be able to summarize. But I was going to ask. I'm trying to be proactive, the ISP(s) may look at this and say "go BGP, we will advertise" - done deal.

Are my concerns about the /24 getting filtered valid?

With the idea of eventually being multihomed - I want to know the pitfalls I face with the single ISP and/or our lack of potential route summarization.

**We are trying to add redundancy and control (traffic shaping and such) to our internet connectivity.** I believe that multi-homed border routers running BGP should help with that...

Thanks for responding,

Rick

[dwyerr]

Hello.

If it's a "true" class C, first three bits 110 or decimal range 192 - 223, you should have no issues. This space has to be accepted.

Where you have to worry about other peoples policy is when you are announcing a subnet of Class A or Class B space. In this case some providers may only accept /23 and larger as a rule.

-Rob

[rsommer]

Thanks Rob. It is true class c space - 198 first octet. I was concerned about people filtering CIDR /24's - and therefore additional hops taken to reach our destination (latency). Probably over-analyzing here...

[ashok_boin]

Hi,

You need to confirm with your ISP first to allow your Class C networks. Major ISPs don't allow them by default.

Coming to multihoming in future, you should talk with your ISPs to transparently advertise your class C networks to outside world.

A big problem which I used to face earlier is one ISP allows transparently our network to outside and another ISP allows only inside their AS but when advertising to outside world, he will do summarize.

The disadvantage with this is you will get inbound traffic only through only one provider always.

Thank you,

Regards...

-Ashok.