[Sidrops] Re: Local AS in ASPA validation (draft-ietf-sidrops-aspa-verification-19)

["Sriram, Kotikalapudi (Fed)" <[e-mail]>]

Hi Maria,

>Looks correct overall.
Great! I think we have converged in this discussion. The only remaining thing perhaps is the following:

>>>In the original definition, the whole summation works because we are indexing from one to N, and we are taking the length of the up and down ramps inclusive of both ends, which is not described anywhere and the “one allowed lateral hop” is well hidden inside the formal definition.

>>[KS:] The draft has this statement in Sec. 6.1: “If there are no hops or just one hop between the apexes of the up-ramp and the down-ramp, then the AS_PATH is valid (valley free).”

>Would you expect an average network engineer, not speaking English daily, to understand this clearly? I have problems parsing the sentence myself.

OK, I have made the following text change in the forthcoming v-21 ( https://github.com/QratorLabs/ASPA/pull/30/commits ):



OLD text (2 paragraphs):



   The AS_PATH may in general have both an up-ramp (on the right

   starting at AS(1)) and a down-ramp (on the left starting at AS(N)).

   The up-ramp starts at AS(1) and each hop AS(i) to AS(i+1) represents

   Customer and Provider peering relationship.  The down-ramp runs

   backward from AS(N) to AS(L).  In the down-ramp, each pair AS(j) to

   AS(j-1) represents Customer and Provider peering relationship.  If

   there are no hops or just one hop between the apexes of the up-ramp

   and the down-ramp, then the AS_PATH is valid (valley free).



   If the sum of lengths of up-ramp and down-ramp is less than N, it is

   invalid: the prefix was leaked or AS_PATH was malformed.



NEW text (2 paragraphs):



   The AS_PATH may in general have both an up-ramp (on the right

   starting at AS(1)) and a down-ramp (on the left starting at AS(N)).

   The up-ramp starts at AS(1) and each hop AS(i) to AS(i+1) represents

   a customer-to-provider peering relationship.  The down-ramp runs

   backward from AS(N) to AS(L).  In the down-ramp, each pair AS(j) to

   AS(j-1) represents a customer-to-provider peering relationship.  If

   the AS_PATH has no up-ramp, it means that K = 1.  If the AS_PATH has

   no down-ramp, it means that L = N.  (Note: The ASPAs are not in

   consideration presently in this description.)  If there are no hops

   or just one hop between the apex AS(K) of the up-ramp and the apex

   AS(L) of the down-ramp, i.e., if L = K or L = K+1, then the AS_PATH

   is valid (valley free).  Otherwise, i.e., if L > K+1, then the

   AS_PATH is invalid (i.e., the prefix was leaked or AS_PATH was

   malformed).



   If one thinks in terms of the lengths of the up-ramp and down-ramp

   (instead of their positions in the AS path as discussed above), then

   it is observed that the up-ramp length is K and the down-ramp length

   is N-L+1 (in terms of number of ASes).  So, it can be alternately

   stated that the AS_PATH is invalid if the sum of the lengths of up-

   ramp and down-ramp is less than N.



Hopefully, this is satisfactory.

Sriram