RE: Static routes in an AS vs BGP advertised routes
If the theoretical AS advertised its /19 itself to the ISPs, and then one of the /24 networks became inaccessible via the asteroid ISP, wouldn't withdrawing the /19 take all traffic off of the asteroid ISP? What if the outage was not an asteroid but something more common, like uncontrolled testing of the network while the stock market is in session? More specifically, what if there was reason to believe the affected ISP could still deliver service in the unaffected areas? I have examined the responses to my query thus far and it seems there are two options: 1) have both ISPs advertise both the /19 and /24s all the time 2) change nothing til the asteroid hits. call the unaffected ISP and have them send out the /24 for the affected site Option 1 creates larger route tables but automatically handles the asteroid situation. Option 2 respects the desire for smaller route tables but requires a manual process of phoning in a service request. In the meantime, the customers served by that connection may receive sub-optimal routing, ie, if the /19 is still advertised by the asteroid ISP, traffic reaches that AS and where does it go? Am I understanding this correctly? If so, this seems to be a case where being internet friendly conflicts with a theoretical entity's desire for uptime. Maybe I am missing something fundamental here though. Comments? Thanks much to those who responded! -----Original Message----- From: Brandon Ross [mailto:bross@netrail.net] Sent: Thursday, August 09, 2001 1:25 PM To: Greg Pendergrass Cc: 'Nanog@Merit. Edu' Subject: RE: Static routes in an AS vs BGP advertised routes On Wed, 8 Aug 2001, Greg Pendergrass wrote:
The problem is if they aggregate and advertise only a /19 instead of individual /24s In this case you could:
- Ask the pulverized ISP to withdraw the aggregate in favor of the specific /24s - Ask your second ISP to advertise your specific /24 in that city
Better yet, advertise your own /19 aggregate, mark your /24's with communities that mean to your provider that they shouldn't be propagated outside of their network and their customers (if they can't do this, fire them) to be a good neighbor by not polluting the global routing table with unnecessary routes. Then when the asteroid hits, just pull down the /19 advertisement (or if you're lucky, they are so destroyed they won't get the announcement out to the world anymore anyway). -- Brandon Ross 404-522-5400 EVP Engineering, NetRail http://www.netrail.net AIM: BrandonNR ICQ: 2269442 Read RFC 2644!
On Thu, 9 Aug 2001, Murphy, Brennan wrote:
If the theoretical AS advertised its /19 itself to the ISPs, and then one of the /24 networks became inaccessible via the asteroid ISP, wouldn't withdrawing the /19 take all traffic off of the asteroid ISP?
It sure would, but in the case of an asteroid strike, I'd assume that there wouldn't be too much reachable through it. In that case you could simply continue to advertise the /19, but of course the stuff in the /24's that are not reachable any longer will end up in the bit bucket. The real question here is, is there internal connectivity between the sites advertising the more specifics, or are they islands? If they are islands, your only real/good solution is to advertise the more specifics only. With a bit of planning, hopefully you can aggregate all the locations that are using a specific upstream into a single block to reduce the number of routes required in the global table. For example if you use 2 different upstreams, you might number all the sites on upstream A into the top /20 and the rest into the bottom /20. If there is internal connectivity, you might just depend on that to cover some backup routes.
What if the outage was not an asteroid but something more common, like uncontrolled testing of the network while the stock market is in session? More specifically, what if there was reason to believe the affected ISP could still deliver service in the unaffected areas?
See above, pretty much all of the possible cases are covered.
I have examined the responses to my query thus far and it seems there are two options: 1) have both ISPs advertise both the /19 and /24s all the time 2) change nothing til the asteroid hits. call the unaffected ISP and have them send out the /24 for the affected site
Option 1 creates larger route tables but automatically handles the asteroid situation. Option 2 respects the desire for smaller route tables but requires a manual process of phoning in a service request. In the meantime, the customers served by that connection may receive sub-optimal routing, ie, if the /19 is still advertised by the asteroid ISP, traffic reaches that AS and where does it go?
The bit bucket.
Am I understanding this correctly? If so, this seems to be a case where being internet friendly conflicts with a theoretical entity's desire for uptime.
That conflict is pretty typical. -- Brandon Ross 404-522-5400 EVP Engineering, NetRail http://www.netrail.net AIM: BrandonNR ICQ: 2269442 Read RFC 2644!
participants (2)
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Brandon Ross -
Murphy, Brennan