[RRG] Commetns about load split in LISP

["Damian Lezama" <damian.lezama@hotmail.com>]

Hello,

In draft-farinacci-lisp-08, section 6.4, there are two things that in my
opinion require improvement and/or clarification:

1)
In the load split algorithm proposed, a hash is used to select a RLOC and it
says "Either a source and destination address hash can be used or the
traditional 5-tuple...". This has important impact in the load split scheme:
if you use only the source IP you are eventually limiting the rate of a
source (and other unlucky hash collisions), if you use the destination IP
you will limit the rate to a destination (and unlucky collisioners), if you
use the 5-tuple (or at least both IPs and ports) you are adopting some kind
of flow (un)fairness... Maybe this requires clarification.

2)
About the selection of a random source UDP port for core routers with LGAs
to load balance (in the same section), as the draft says, if core routers
see a single flow they don't split-load. Random port selection would make
those routers to "break" flows, but they don't want to do that, is that
because they know it's not good?
I think the random selection could be changed for a hash as in the case
mentioned above (and maybe unify the criteria about which part of the
5-tuple to use). This may be a must if: there are core routers
load-splitting between links with different characteristics or there are
layer 3 load balancers choosing different paths (maybe even a recursive LISP
re-tunneling). In these cases the flows can get very damaged (poor RTT
estimation, serious reordering, etc.)

I hope my comments could be useful. All feedback is welcome. Thanks.

Regards,
Damian Lezama



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