Issue with filter generation with aggregate about bgpq3 HOT 4 CLOSED

from bgpq3.

This is an interesting situation. The -A flag (or a request to aggregate) could be interpreted in two different ways.

1. There's aggregation in the form of how the originating network decides it wants to aggregate.
2. There's aggregation where it means "I (the operator of the filters) want to aggregate, independent of the originating network, in how I create filters.

Both of you are right. Presently the code and it's -A flag means the first item above. However, there's a case to be made for a second/different flag to implement the second case.

In fact there's even a case when aggregation should always be used; both for router optimization and for terseness of filter output. It took a while to find a good example of this; but I think this ASN could show a valid case (just ignore the /24 for now).

$ bgpq3 -JE -l foo AS201890
policy-options {
 policy-statement foo { 
replace:
  from {
    route-filter 188.123.112.0/22 exact;
    route-filter 188.123.112.0/23 exact;
    route-filter 188.123.113.0/24 exact;
    route-filter 188.123.114.0/23 exact;
  }
 }
}
$

wth the -A aggregate flag you get less output:

$ bgpq3 -JEA -l foo AS201890
policy-options {
 policy-statement foo { 
replace:
  from {
    route-filter 188.123.112.0/22 upto /23;
    route-filter 188.123.113.0/24 exact;
  }
 }
}
$

What I'm trying to show, with this ASN, is that because there's two /23's and one /22 one can always aggregate into one line (the upto /23 part).

Back to the question in hand.

I also believe there's a case (as shown by @anuragbhatia above) where a set of (lets say, his four /24's) could be aggregated by bgpq3 into a single /22 and accept any route within any of the /22 space. This is very much up to the operator of the filters vs. the originator of the routes. The automatic aggregation is very specific to the filter operator.

If this was implemented; I would vote for a different command line flag than the existing -A flag.

BTW: There's a good example of complex filtering based on mask length in the real world. The INEX Internet Exchange in Dublin Ireland has very strict filtering on it's route server. However many other Internet Exchanges are less strict and accept upto /24 automatically. Either way - the request above is more about filter optimization.

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