Florian: > Are the autonomous systems for the /19 and /24 connected directly?
Yes they are. > (1) can be better from B's perspective because it prevents certain routing > table optimizations (due to the lack of the covering prefix) What kind of routing table optimizations are possible if covering /19 prefix is also present in global routing table? > But (1) can also be worse for B and A's other customers if /24s (and slightly > shorter prefixes) in this part of the IPv4 address space are commonly > filtered. Based on my experience /24 is allowed in prefix-filters.. Longer IPv4 prefixes are not. Roy, Mel: Could you please elaborate on that option. What kind of advantages does this have compared to option 2? thanks, Martin On Tue, Sep 27, 2016 at 8:52 PM, Michael Hallgren <m...@xalto.net> wrote: > Hi Martin, > > What do you want to do? Move from A to B or add A to B? > > Cheers, > mh > > > > Le 27 sept. 2016 17:52, à 17:52, Mel Beckman <m...@beckman.org> a écrit: >>Precisely. This is how it's done by providers I've worked with. >> >> -mel beckman >> >>> On Sep 27, 2016, at 7:06 AM, Roy <r.engehau...@gmail.com> wrote: >>> >>> >>> >>> Option 3? >>> >>> ISP A announces the /19 and the /24 while ISP B does just the /24 >>> >>>> On 9/27/2016 4:20 AM, Martin T wrote: >>>> Hi, >>>> >>>> let's assume that there is an ISP "A" operating in Europe region who >>>> has /19 IPv4 allocation from RIPE. From this /19 they have leased >>/24 >>>> to ISP "B" who is multi-homed. This means that ISP "B" would like to >>>> announce this /24 prefix to ISP "A" and also to ISP "C". AFAIK this >>>> gives two possibilities: >>>> >>>> 1) Deaggregate /19 in ISP "A" network and create "inetnum" and >>"route" >>>> objects for all those networks to RIPE database. This means that ISP >>>> "A" announces around dozen IPv4 prefixes to Internet except this /24 >>>> and ISP "B" announces this specific /24 to Internet. >>>> >>>> 2) ISP "A" continues to announce this /19 to Internet and at the >>same >>>> time ISP "B" starts to announce /24 to Internet. As this /24 is >>>> more-specific than /19, then traffic to hosts in this /24 will end >>up >>>> in ISP "B" network. >>>> >>>> >>>> Which approach is better? To me the second one seems to be better >>>> because it keeps the IPv4 routing-table smaller and requires ISP "A" >>>> to make no deaggregation related configuration changes. Only bit >>weird >>>> behavior I can see with the second option is that if ISP "B" stops >>for >>>> some reason announcing this /24 network to Internet, then traffic to >>>> hosts in this /24 gets to ISP "A" network and is blackholed there. >>>> >>>> >>>> thanks, >>>> Martin >>>
