I absolutely concur that a block smaller than a /24 will not work for a
bgp setup. This is why some providers will give you a /24 if you are
going to do bgp. The filtering of routes into the bgp table is somewhat
complex. For example, at a former employer, If a route was out of what
used to be classful A space and mask greater than a /20, it'd get
chucked. Routes out of what used to be classful B space would get chucked
if the mask were greater than /21.
Brian
On Fri, 13 Oct 2000, Brian wrote:
> On Fri, 13 Oct 2000, John Neiberger wrote:
>
> > I have a question that I'm sure has been referenced before but I couldn't
> > find an answer in the archives, and it's more practical than technical.
> >
> > We have a single T-1 connection to an ISP for customer access to our
> > internal webservers so that our banking customers can do web-based
> > transactions and get account information. This is such an important aspect
> > of our business that we decided to get a second T-1 to another ISP for
> > redundancy. We aren't as concerned with being able to load-balance, which
> > is a dicey prospect in this arrangement anyway.
> >
> > Now, the problem: we have a tiny subnet assigned to us from ISP-1, it's a
> > /27. Now let's say we get a connection to ISP-2 and we start running BGP.
> > Is ISP-2 probably going to have a problem letting us advertise such a small
> > set of routes? I've been hearing that big ISPs tend not to want to
>
> most definitly.........it would be hard to get them to do it, and everyone
> is going to filter a /27 announcement, if someone leaked a /27 into the
> global table, they would get jumped on fast :)
>
> > advertise subnets smaller than a /18. If that's the case, our plan is in
> > trouble.
>
> thats a bunch of BS for the most part. their are plenty of /24's being
> announced just fine, with lots of connectivity........the few sticklers
> out there generally are even more liberal than the /18.....more like /20,
> /21....
>
> >
> > Now, problem #2: even if we can advertise a /27 through ISP-2, ISP-1 is
> > going to have to agree to advertise our /27 along with their aggregate
> > advertisement. If they don't, and they only advertise their aggregate, this
> > will cause return traffic to our network to come through ISP-2 because it
> > will be advertising a more specific route, correct? If that's correct, do
> > ISPs tend to have a problem with this arrangement?
>
> you are going to have problems with a /27. You could run multiple
> redundant local loops to a single ISP that is multi-homed real well.
>
> >
> > Basically, are we setting ourselves up for disappointment? Are there any
> > other factors that I should be aware of that I'm not considering? Should I
> > become a yak herder and move to Nepal?
>
> You have some options. How large is your company? Could they possibly
> justify a larger block assignment from either ARIN or the ISP?
>
> Brian
>
>
>
>
> >
> > Thanks, as usual...
> > John Neiberger
> >
> >
> >
> >
> >
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>
> -----------------------------------------------
> Brian Feeny, CCNP, CCDP [EMAIL PROTECTED]
> Network Administrator
> ShreveNet Inc. (ASN 11881)
>
> _________________________________
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