SDN Internet Router (sir)

Mike Hammett nanog at
Fri Jan 6 15:29:22 UTC 2023


I don't need any additional performance tests, though. Just watching which prefixes are the top talkers and leaving the rest to default. 

I'm not looking at this to do what a BGP optimizier would do and find the best tested path to the top talkers and then massage BGP to get it routed that way. Determine the top talkers, then let BGP do its thing for those top talkers. 

I don't want to manually say X traffic from Y POP manually goes here, but I don't want to just leave it to default routing either. Something in the middle. 

Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 

----- Original Message -----

From: "Tom Beecher" <beecher at> 
To: "Mike Hammett" <nanog at> 
Cc: "Mel Beckman" <mel at>, "NANOG" <nanog at> 
Sent: Friday, January 6, 2023 9:16:19 AM 
Subject: Re: SDN Internet Router (sir) 

Thanks for this example. 

It sounds like you are describing egress peer engineering, but kinda in reverse. 

In 'traditional' EPE, the routers have all the routes, and you are using the external controller to perform the performance tests that matter to you, and signal the network where to take the traffic based on those tests. 

It seems like you want to do the same thing , but instead of having the controller signal the network where to carry bits, you want the controller to signal the networks what routes are present, and direct the bits that way. 

Do I have this right? 

On Thu, Jan 5, 2023 at 4:12 PM Mike Hammett < nanog at > wrote: 

I hesitated to get too specific in examples because someone is going to drag the conversation into the weeds. 

Let's take the the Dallas - New Orleans - Atlanta example where I have a connection from New Orleans to Dallas and a connection from New Orleans to Atlanta. 

Let's say I peer with Netflix in both markets. Netflix chooses to serve me out of Atlanta, for whatever reason. Say my default route sends my traffic to Dallas. That's not where Netflix wanted it, so now I have to go from Dallas to Atlanta, whether that's my circuit or across the public Internet. Potentially, it's on MPLS and it rides back through the New Orleans router to get back to Atlanta. That's a long trip when I already had a better path, the less-than-full-fib router just didn't know about it. Given that Netflix is a sizable amount of traffic in an eyeball ISP, that's a lot of traffic to be going the wrong way. If the website for Viktor's Arctic Plunge in Siberia was hosted in Atlanta, I wouldn't give two craps that the traffic went the wrong way because A), I'll probably never go there and B) when someone does, it won't be meaningfully enough traffic to accommodate. 

Someone's going to tell me to put a full-table router in New Orleans. Maybe I should. Okay, so maybe I have a POP in Ashford, Alabama. It has transport to New Orleans and Atlanta. There aren't enough grains of sugar in Ashford, Alabama to justify a current-generation, full table router. Now I'm even closer to Atlanta, but default may point to New Orleans. 

Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 

From: "Mel Beckman" < mel at > 
To: "Mike Hammett" < nanog at > 
Cc: "Joe Maimon" < jmaimon at >, "NANOG" < nanog at > 
Sent: Thursday, January 5, 2023 2:54:27 PM 
Subject: Re: SDN Internet Router (sir) 


I’m not sure I understand what you mean by “suboptimal“ routing. Even though the Internet uses AS path length for routing, many of those path lengths are bogus, and don’t really represent any kind of path performance value. For example, a single AS might hide many hops in an MPLS network as a single hop, obscuring asymmetric routing and other uglies. Prepending also occurs when destinations are trying to enforce their own engineering policies, which often conflict with yours or mine. 

So what do you mean by “suboptimal“? Are you thinking that the “best” path in BGP tables actually meant you were getting a performance benefit? Because that’s definitely not the case in today’s Internet. Were were you thinking that you would be going along less congested paths? That’s really at the mercy of the traffic engineering of backbone providers over which we have no control. 

I generally populate local router FIBs to merel choose an exit point for purposes of load balancing, and nothing more. 


On Jan 5, 2023, at 12:38 PM, Mike Hammett < nanog at > wrote: 


I guess I wasn't around for those days. 

As far as running out, again, assuming the tooling works correctly, I'd think to target fewer routes than you could hold. Maybe 1k routes is all one would need to get a significant percent of the traffic. A lot of room to mess up if you can hold 100k, 500k routes. 

Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 

From: "Joe Maimon" < jmaimon at > 
To: "Mike Hammett" < nanog at >, "Christopher Morrow" < morrowc.lists at > 
Cc: "NANOG" < nanog at > 
Sent: Thursday, January 5, 2023 2:30:40 PM 
Subject: Re: SDN Internet Router (sir) 

Mike Hammett wrote: 
> I'm not concerned with which technology or buzzword gets the job done, 
> only that the job is done. 
> Looking briefly at the couple of things out there, they're evaluating 
> the top X prefixes in terms of traffic reported by s-flow, where X is 
> the number I define, and those get pushed into the FIB. One 
> recalculates every hour, one does so more quickly. How much is 
> appropriate? I'm not sure. I can't imagine it would *NEED* to be done 
> all of that often, given the traffic/prefix density an eyeball network 
> will have. Default routes carry the rest. Default routes could be 
> handled outside of this process, such that if this process fails, you 
> just get some sub-optimal routing until repaired. Maybe it doesn't 
> filter properly and sends a bunch of routes. Then just have a prefix 
> limit set on the box. Maybe it sends the wrong prefixes. No harm, no 
> foul. If you're routing sub-optimally internally, when it does hit a 
> real router with a full FIB, it gets handled appropriately. 

Unless it loops. 

The rest sounds nice. But flow caching got a bad rap back in the early 
worm days. But thats because the situation was a little worse back then. 
Cache the wrong routes or run out of cache, router dies. So long as 
thats not the case automating optimization is an extremely valuable goal. 

> I would just be looking for solutions that influence what's in the FIB 
> and let the rest of the router work as the rest of the router would. 

The problem comes when the router wont work at all without the FIB 
routes, like in the olden days. 
> ----- 
> Mike Hammett 
> Intelligent Computing Solutions < > 
> < >< >< >< > 
> Midwest Internet Exchange < > 
> < >< >< > 
> The Brothers WISP < > 
> < >< > 
> ------------------------------------------------------------------------ 
> *From: *"Christopher Morrow" < morrowc.lists at > 
> *To: *"Mike Hammett" < nanog at > 
> *Cc: *"Tom Beecher" < beecher at >, "NANOG" < nanog at > 
> *Sent: *Thursday, January 5, 2023 12:27:08 PM 
> *Subject: *Re: SDN Internet Router (sir) 
> On Thu, Jan 5, 2023 at 11:18 AM Mike Hammett < nanog at 
> <mailto: nanog at >> wrote: 
> Initially, my thought was to use community filtering to push just 
> IXes, customers, and defaults throughout the network, but that's 
> obviously still sub-optimal. 
> I'd be surprised if a last mile network had a ton of traffic going 
> to any more than a few hundred prefixes. 
> I think in a low-fib box at the edge of your network your choices are: 
> "the easy choice, get default, follow that" 
> "send some limited set of prefixes to the device, and default, so 
> you MAY choose better for the initial hop away" 
> you certainly can do the second with communities, or route-filters 
> (prefix-list) on the senders, or.... 
> you can choose what prefixes make the cut (get the community(ies)) 
> based on traffic volumes or expected destination locality: 
> "do not go east to go west!" 
> these things will introduce toil and SOME suboptimal routing in some 
> instances... perhaps it's better than per flow choosing left/right 
> though and the support calls related to that choice. 
> In your NOLA / DFW / ATL example it's totally possible that the 
> networks in question do something like: 
> "low fib box in tier-2 city (NOLA), dfz capable/core devices in 
> tier-1 city (DFW/ATL), and send default from left/right to NOLA" 
> Could they send more prefixes than default? sure... do they want to 
> deal with the toil that induces? (probably not says your example). 
> SDN isn't really an answer to this, though.. I don't think. Unless you 
> envision that to lower the toil ? 



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the NANOG mailing list