> Unless it's built at a lower layer than a piggy-back app, it's going to be a > scale monster (IMO, if you plan for success, then ultimately you have highly > connected NVEs - hello scale monster). Something like CFM for overlays > (logical ethernet, logical continuity check built into your header as a > special packet type, punt to momma NVE process ...not some cousin, etc?)? > =8^)
Definitely agree Ken. See LISP echo-noncing. I pulled some text out of RFC 6830 and pasted below. Dino ------ 6.3.1. Echo Nonce Algorithm When data flows bidirectionally between Locators from different sites, a data-plane mechanism called "nonce echoing" can be used to determine reachability between an ITR and ETR. When an ITR wants to solicit a nonce echo, it sets the N- and E-bits and places a 24-bit nonce [RFC4086] in the LISP header of the next encapsulated data packet. When this packet is received by the ETR, the encapsulated packet is forwarded as normal. When the ETR next sends a data packet to the ITR, it includes the nonce received earlier with the N-bit set and E-bit cleared. The ITR sees this "echoed nonce" and knows that the path to and from the ETR is up. The ITR will set the E-bit and N-bit for every packet it sends while in the echo-nonce-request state. The time the ITR waits to process the echoed nonce before it determines the path is unreachable is variable and is a choice left for the implementation. If the ITR is receiving packets from the ETR but does not see the nonce echoed while being in the echo-nonce-request state, then the path to the ETR is unreachable. This decision may be overridden by other Locator reachability algorithms. Once the ITR determines that the path to the ETR is down, it can switch to another Locator for that EID-Prefix. Note that "ITR" and "ETR" are relative terms here. Both devices MUST be implementing both ITR and ETR functionality for the echo nonce mechanism to operate. The ITR and ETR may both go into the echo-nonce-request state at the same time. The number of packets sent or the time during which echo nonce requests are sent is an implementation-specific setting. However, when an ITR is in the echo-nonce-request state, it can echo the ETR's nonce in the next set of packets that it encapsulates and subsequently continue sending echo-nonce-request packets. This mechanism does not completely solve the forward path reachability problem, as traffic may be unidirectional. That is, the ETR receiving traffic at a site may not be the same device as an ITR that transmits traffic from that site, or the site-to-site traffic is unidirectional so there is no ITR returning traffic. The echo-nonce algorithm is bilateral. That is, if one side sets the E-bit and the other side is not enabled for echo-noncing, then the echoing of the nonce does not occur and the requesting side may erroneously consider the Locator unreachable. An ITR SHOULD only set the E-bit in an encapsulated data packet when it knows the ETR is enabled for echo-noncing. This is conveyed by the E-bit in the Map-Reply message. Note that other Locator reachability mechanisms are being researched and can be used to compliment or even override the echo nonce algorithm. See the next section for an example of control-plane probing. ------ _______________________________________________ nvo3 mailing list [email protected] https://www.ietf.org/mailman/listinfo/nvo3
