I agree that IXPs could be connected. Let me explain the problem more clear. Suppose the following example. ISP A has a router A1 in IXP1 and a router A2 in IXP2; and ISP B has a routers B1 in IXP1 and a router B2 in IXP2. It is possible that we have DIRECT link A1A2 and B1B2 to connnect two IXPs, but I don't think there may be DIRECT link like A1B2 or A2B1. Since it should be much cheaper and easier for ISP A and ISP B to be connnected in the same IXP using links like A1B1 or A2B2. Am I right? So in your case, all the suppliers and peers DIRECTLY connected to any one of your routers are located in the same IXP? ------------------------------------------------------------- From: Tuc at T-B-O-H.NET Data: 2007-11-29 19:29:12 To: huc@ieee.org CC: Subject: [nanog] Connections among ASes (fwd)
Hi,
I am not sure about whether the following two conditions are true or not:
1) there is no such a direct link between two routers located in two Internet eXchange Points-IXPs (even in same city) if they are from different ASes. For example, a router A belongs to AS x located in IXP1, and router B belongs to AS y located in IXP2, there is no link between A and B. 2) small AS will not use one router to connect to 2 different providers in differnet IXPs. It is much cheaper using one router to connect with different ASes in a same IXP.
Hi, REPLY IS OFFLIST.......... Not quite sure I understand this... But, giving the old college try (Even though I didn't go to college)... Just because someone is at an IX, doesn't mean they peer with EVERYONE on the IX. IX's can also be interconnected, so even though ISP1 is at IX1 in 1 place, and ISP2 is at IX2 in place #2, they potentially COULD be interconnected but don't HAVE to be. IX's inherently aren't interconnected, but there are some places where they are. NYIIX has 2 sites. NYCX has 3. NYIIX and LAIX were supposed to be tied together, but not sure if it ever happened. As for small ISP with 1 router... When we were at the NYIIX, we had 1 router (Cisco 6509) and connected to 3 bandwidth suppliers AND ~40 peers at the NYIIX. We also had 2 routers, both were connected to each other, as well as both to our suppliers + our Peers at the NYIIX peered at 2 addresses with us. We had redundant routers, so never saw the need to split functionality apart. Tuc
On Thu, 29 Nov 2007 20:49:13 CST, Chengchen Hu said:
Suppose the following example. ISP A has a router A1 in IXP1 and a router A2 in IXP2; and ISP B has a routers B1 in IXP1 and a router B2 in IXP2. It is possible that we have DIRECT link A1A2 and B1B2 to connnect two IXPs, but I don't think there may be DIRECT link like A1B2 or A2B1. Since it should be much cheaper and easier for ISP A and ISP B to be connnected in the same IXP using links like A1B1 or A2B2. Am I right?
You're quite possibly wrong - for instance, if I'm ISB B, I *might* want to have a direct peering session between A1 and B1 - but *also* have a connection from B1 over to the *other* router A2, for several reasons: 1) I may know that the *next* router hop after A1 has questionable reliability, and thus I want a fall-over to A2, which has better connectivity upstream. 2) I may be able to get a second link over to A2 for "essentially free" because I have a connection to IXP2 because I peer with *another* provider C (who I have to connect at IXP2 because C has no presence in IXP1). At that point, I may be able to get B1-C2 for some cost - and then B1-A2 as a backup to the B1-A1 is almost free at some IXPs - just one interconnect across the room. 3) Due to traffic balance quirks (maybe I'm content-heavy at IXP1 and eyeball-heavy at IXP2), I may qualify for peering at one IXP but not the other - so if my only peering is at IXP2, I have to haul traffic from IXP1 to IXP2 and peer there. (Yes, that *would* be odd - but I've seen stranger stuff happen with peering.. ;) 4) Traffic engineering may indicate that doing a cross-connect may be faster/better - if you have a lot of traffic from your AS hitting router A1, but the *other* end is just upstream of B2, you have 2 choices: a) dump the traffic from A1 to B1 and let them haul it to B2 (hot potato routing). This can suck if B1-B2 is congested... b) Put in your own link from A1 to A2/B2 - this can win if your A1-B2 is less loaded than B1-B2 is. I'm sure that the guys who do the traffic engineering thing for a living can come up with even more examples why it may be different...
So in your case, all the suppliers and peers DIRECTLY connected to any one of your routers are located in the same IXP?
In our case, we have routers inside our AS1312 - and our two main next-hops (Level3 and NetworkVirginia) are both at the other end of many miles of fiber.
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Chengchen Hu -
Valdis.Kletnieks＠vt.edu