On Fri, Feb 22, 2008 at 9:58 AM, Robin Whittle <[EMAIL PROTECTED]> wrote: > http://bill.herrin.us/network/trrp-aapip.html > > In both your system and this use of ALT, ITRs are not involved and > no mapping information is required.
Hi Robin, Actually ITRs are involved for TRRP. The idea is that if an ETR for a packet isn't yet known but a highly aggregated waypoint for that block of address space (perhaps a /8) is already known then you can move the packet closer to its destination immediately. A waypoint is a combination ETR/ITR. It can accept packets with any encapsulation that it advertises and will if necessary re-encapsulate them in a manner that the next waypoint or final destination accepts. Because there are perhaps a couple hundred top-level waypoints (compared to millions of final destination ETRs) and because waypoint maps have a long timeout it's highly probable that the ITR has already cached a valid waypoint. If it hasn't, the ITR has a search algorithm that guarantees it quickly will. > Can you give a more concrete example of how these Waypoint Routers > would be structured? Sure. Lets say we have a source IP at 126.0.0.1 and he want's to talk to me in the swamp at 199.33.224.1. So, he sends the packet out. Call it packet A. There is no BGP route that covers 199.33.224.1, so packet A follows 0.0.0.0/0 to the nearest TRRP ITR. The ITR doesn't yet have a map for 199.33.224.1. However, he does have a waypoint map for 199.0.0.0/8: apparently the US Government has decided to be nice and offer an "initial" mode GRE waypoint as a public service at 148.129.75.8, which is within globally routable (BGP routed) space. So, the ITR immediately encapsulates packet A in GRE and sends it to 148.129.75.8. Then it initiates a lookup for 1.224.33.199.v4.trrp.arpa so that it'll be able to send subsequent packets directly. 148.129.75.8 doesn't have a MAP for 199.33.224.1 either. However, I have a private waypoint set up for all of 199.33.224.0/23 in "generous" mode at 71.246.241.146 (which is also within globally routeable space). It accepts GRE as one if its formats. I have made arrangements with 148.129.75.8 to keep this knowledge in his cache. Essentially, I push this knowledge to him. So, 148.129.75.8 keeps packet A in GRE and sends it on to my waypoint at 71.246.241.146. He doesn't bother trying to look up 1.224.33.199.v4.trrp.arpa because I've told him that my waypoint operates in "generous" mode. My waypoint at 71.246.241.146 receives packet A. He's directly attached to an authoritative DNS server that knows the current TRRP map for 1.224.33.199.v4.trrp.arpa and probably already has it in his cache. In this case, it happens to be directly available (the waypoint was also a final ETR) so 71.246.241.146 decapsulates packet A and delivers it to 199.33.224.1. Around the same time, the DNS request for 1.224.33.199.v4.trrp.arpa from the original ITR reaches the authoritative DNS server and the reply starts making its way back. Note that US Government could have been replaced with Money Grubbing Company and "initial" mode could have been replaced with "limited" mode. The differences would have been: 1. The first ITR would have held a copy of packet A and would have sent a second copy once the map lookup for 1.224.33.199.v4.trrp.arpa succeeded. 2. If I didn't pay MGC to pass my packets to me, he would have dropped packet A instead of sending it on to my waypoint. I'd have had to wait for the ITR's second copy. Note also that 148.129.75.8 would likely announce 199.0.0.0/8 into the BGP table so that networks without TRRP ITRs could find their way to my TRRP ETR. How exactly we do this is an open issue, one of the unfinished things about the document... Any network which -does- have a TRRP ITR shouldn't insert that route into its FIB, or should locally override it from the ITR. How does it know to do so? It's my "holey routes" problem wrought large. > To what extent does your system resemble ALT, and to what extent > does my critique of ALT apply to your system? Without having reviewed ALT in any detail, my best guess is that it doesn't share much besides the notion of a highly aggregated alternate path. ALT sounds like it might work with static tunnels or private lines using something close to standard BGP. On the down side, it would require a complex dance between thousands of operators to get it going. With Waypoints, the complex dance is at the RIR public policy level getting authorization to announce for that supernet. Once authority is obtained, they hook up at any old place and announce the prefix. > By your own description, the Waypoint Router path is "long" - > compared to going direct in a tunnel to the ETR (the address of > which is not known at this time). Presumably this "long" path will > be faster than waiting for the mapping information to arrive. > > Do you have estimates for the delay times? My SWAG is that the initial round trip will be 1.5 to 2 times the normal round trip with some single-digit percentage taking long enough to recognize no gain versus bare TRRP. Regards, Bill Herrin -- William D. Herrin [EMAIL PROTECTED] [EMAIL PROTECTED] 3005 Crane Dr. Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004 -- to unsubscribe send a message to [EMAIL PROTECTED] with the word 'unsubscribe' in a single line as the message text body. archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg
