nanog mailing list archives
Re: Long AS Path
From: Stephen Satchell <list () satchell net>
Date: Thu, 22 Jun 2017 06:29:33 -0700
On 06/22/2017 04:27 AM, Jon Lewis wrote:
You do have to wonder, what was the thought process that resulted in 35 being the right number of prepends "accomplish" whatever TE they were shooting for? AS path: 10026 9498 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 55644 45271 I don't mean to single out 55644. It's just the first/most obnoxiously long as-path I found when looking for long ones. I seriously doubt provider/customer/customer-of-customer relationships ever get much deeper than a handful or so of ASNs...so if prepending a few times doesn't get it done, 10-20-30 prepends are unlikely to help. In the above case, that long path is actually our best path. We localpref peering above transit. So, it doesn't matter how many prepends, they add, we're never going to not use this path if its available. We have transit paths to these routes that are only a single handful of ASNs long.
I think I understand the problem, and now I understand why prepends didn't do much for me. Over the years, I tended two multi-homed sites. In both cases, the two uplinks had different speeds. When I used prepend to try to get the outside world to prefer the faster link, some traffic was stubborn about coming in the slow one. Difference in speeds? In the first network it was 45 mbps and 10 mbps. In the second network it was 16 mbps and 1.5 mbps. Both network owners were too stingy at the time to opt for harmonized rates. Question: how could communities be used to "force" preference for one uplink over another by the peers? I'm long past needing this, but others might benefit. (And when you stop learning, you're dead.)
Current thread:
- Re: Long AS Path, (continued)
- Re: Long AS Path Stephen Satchell (Jun 21)
- Re: Long AS Path sthaug (Jun 21)
- Re: Long AS Path Mel Beckman (Jun 21)
- Re: Long AS Path Pierfrancesco Caci (Jun 21)
- Re: Long AS Path jim deleskie (Jun 22)
- Re: Long AS Path Mel Beckman (Jun 22)
- Re: Long AS Path Stephen Satchell (Jun 21)
- Re: Long AS Path Bob Evans (Jun 21)
- Re: Long AS Path Saku Ytti (Jun 21)
- Re: Long AS Path Jon Lewis (Jun 22)
- Re: Long AS Path Stephen Satchell (Jun 22)
- Re: Long AS Path Ryan L (Jun 23)