OSPF Optimized Multipath (OSPF-OMP) Curtis Villamiza r < - - PowerPoint PPT Presentation

ospf optimized multipath ospf omp curtis villamiza r
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OSPF Optimized Multipath (OSPF-OMP) Curtis Villamiza r < - - PowerPoint PPT Presentation

OSPF Optimized Multipath (OSPF-OMP) Curtis Villamiza r < curtis@ans.net > URLs (including ea rlier simulations): http://engr.ans.net/mpls-omp { http://engr.ans.net/ospf-omp { http://engr.ans.net/isis-omp { Internet


slide-1
SLIDE 1 OSPF Optimized Multipath (OSPF-OMP) Curtis Villamiza r <curtis@ans.net>
  • URLs
(including ea rlier simulations): { http://engr.ans.net/mpls-omp { http://engr.ans.net/ospf-omp { http://engr.ans.net/isis-omp
  • Internet
Drafts: { draft-ietf-ospf-omp-01.txt,ps { draft-villamiza r-isis-omp-00.txt,ps { draft-villamiza r-mpls-omp-00.txt,ps
  • This
is {still{ \w
  • rk
in p rogress".
slide-2
SLIDE 2 Draft Status: draft-ietf-ospf-omp-01.txt,ps
  • Changes
since the
  • 00
version: { Do cument reo rganized fo r b etter readabilit y { Mino r changes to pa rameters from simulation exp erience { Option to relax SPF b est path criteria (Dave W a rd) { Pseudco de included in app endices to aid implemento rs
  • Up
coming changes: { Optimization
  • f
pa rtial paths
  • Multiple
vendo rs considering implementation. { Not sure if any have sta rted co ding.
slide-3
SLIDE 3 OMP Algo rithm Highlights
  • Flo
  • d
Loading Info rmation via OSPF
  • r
IS-IS { Router samples
  • wn
SNMP counters every 15 seconds { Filters and
  • ds
dep ending
  • n
load level and change
  • F
  • rw
a rding (OSPF-OMP , ISIS-OMP , MPLS-OMP at ingress) { Compute Hash
  • n
IP source/destination { Select from available paths based
  • n
hash value { 14-16 bit hash p rovides ne adjustment granula rit y
  • Load
Adjustment (OSPF-OMP , ISIS-OMP , MPLS-OMP) { load adjustment through change in hash b
  • unda
ry { small initial adjustment { exp
  • nential
increase in adjustment increment { increment is halved when adjustment reverses
  • P
ath Setup (MPLS-OMP
  • nly)
{ Setup new paths after p ersistent high utilization { Remove extra paths after p ersistent lo w utilization { TE do es not dep end
  • n
ca reful conguration
  • f
IGP link metrics
slide-4
SLIDE 4 Flo
  • d
Loading Info rmation via OSPF
  • r
IS-IS
  • Router
samples
  • wn
SNMP counters every 15 seconds { Counters a re iffIn,OutgfOctets,P ack et,Disca rdg
  • Filter
using a few compa re, shift, and add
  • p
erations
  • Compute
\equivalent load" as describ ed in OSPF-OMP
  • Check
fo r reo
  • ding
based
  • n:
{ Time elapsed since last
  • ding
{ Greater
  • f
current load and last
  • ded
value { P ercent change since last
  • ded
value
  • When
needed, reo
  • d
and reco rd time and value
slide-5
SLIDE 5 F
  • rw
a rding (OSPF-OMP , ISIS-OMP , MPLS-OMP at ingress)
  • After
SPF create \next hop" data structures
  • Compute
Hash
  • n
IP source/destination p er pack et { 14-16 bit hash p rovides ne adjustment granula rit y { CRC16 seems to w
  • rk
ne. Others ma y b e used.
  • Select
from available paths based
  • n
hash value { Compa re hash value to b
  • unda
ries in \next hop" struct { F
  • rw
  • rding
is lik e ECMP except load split is unequal { Adjustments to b
  • unda
ries will adjust load split
  • Cha
racteristics: { No transient routing lo
  • ps
  • r
drops { No microo w pack et reo rdering except during adjustment { Adjustments a re every few minutes (minimal reo rdering)
slide-6
SLIDE 6 Load Adjustment (OSPF-OMP , ISIS-OMP , MPLS-OMP)
  • Load
adjustment through change in hash b
  • unda
ry
  • Initial
adjustment a re very small (default is 1%)
  • Additional
adjustments a re made: { When loading
  • n
the most heavily loaded link is reo
  • ded
{ After timers expire and no change is rep
  • rted
  • The
adjustment increment increases exp
  • nentially
{ When signicant adjustment
  • ccurs,
  • ding
is fo rced { Flo
  • ding
will either accellerate
  • r
reverse adjustment
  • Some
  • versho
  • t
can
  • ccur
when trac rapidly ramps up
  • When
adjustment reverses, adjustment increment is halved { Halving the rate
  • n
reversal insures stabilit y { Stabilit y has not b een mathematically p roven, but simu- lation results strongly indicate stabilit y { When load stabilizes,
  • ding
rate also drops
slide-7
SLIDE 7 OSPF-OMP when used with MPLS-OMP
  • Besides
doing what OSPF no rmally do es, an interio r router in an MPLS-OMP domain do es the follo wing: { Sample its
  • wn
SNMP counters every 15 seconds. { Apply simple lter to SNMP sampled data. { Determine when to
  • d
itered result acco rding to guidelines in OSPF-OMP
  • Ingress
routers must also do the follo wing: { Setup MPLS LSP path sets acco rding to MPLS-OMP { Adjust loading
  • n
path sets acco rding to OSPF-OMP { Hash
  • n
src/dst and fo rw a rd acco rding to OSPF-OMP
slide-8
SLIDE 8 A Simple Example

F B D G E C A

2 2 2 2 2 2 3 6 2

  • Majo
r ingress and egress a re A, F and E, G
  • Majo
r
  • ws
a re A-E = F-G = F-E = 0.5, A-G = 1
  • Link
E-G is double capacit y
  • f
  • thers
  • Link
costs a re as sho wn in the circles
  • Utilizations:
Red = 1, Green = 0.5
slide-9
SLIDE 9 First Opp
  • rtunit
y fo r Load Adjustment

F B D G E C A

  • No
de B can move load from B-D-E to B-C-E
  • Utilizations
  • f
B-C, C-E, and D-E app roach 0.75
  • Utilizations
  • f
B-D drops to 0.25
slide-10
SLIDE 10 Second Opp
  • rtunit
y fo r Load Adjustment

F B D G E C A

  • No
de F can move load from F-G to F-D-E
  • No
de B will continue to move load from B-D-E to B-C-E
  • Utilizations
  • f
B-C, C-E, and D-E, F-G app roach 0.83
  • Utilizations
  • f
F-G and E-G app roach 0.67
  • No
de F will actually not w ait until D-E loading has reached 0.75, it will sta rt moving load when D-E loading is noticed to b e lo w er than F-G
slide-11
SLIDE 11 Second Opp
  • rtunit
y fo r Load Adjustment

F B D G E C A

  • No
de A can move load from A-B-fCDg-E-G to A-F-G
  • No
de F will continue to move load fro F-G to F-D-E
  • No
de B will continue to move load from B-D-E to B-C-E
  • Utilization
  • f
A-B will app roach 0.83
  • Utilizations
  • f
F-G and E-G also app roach 0.83
  • No
de A will sta rt moving load when F-G loading is noticed to b e lo w er than A-B
  • A-F
go es to 0.67, B-D app roaches zero
slide-12
SLIDE 12 The Need fo r P a rtial P ath Optimization

B D G E C A F

2 2 2 2 2 3 2 6 2

  • Consider
trac in the reverse direction
  • W
  • rst
loading
  • n
the E-C-B-A path load
  • f
1.0
  • n
D-A
  • W
  • rst
loading
  • n
the E-D-B-A path is
  • n
D-A and E-D
  • Moving
load from E-D-B-A to E-C-B-A do es not reduce load
  • n
the link D-A so it do es not reduce the load
  • n
E-D-B-A.
  • No
de E will not move load from E-D-B-A to E-C-B-A
slide-13
SLIDE 13 V alidating the Algo rithms
  • Simulations
a re at http://engr.ans.net/ospf-omp { tuto rial directo ry has simple examples { simulations directo ry has la rger top
  • logies
{ simulations directo ry has adverse conditions cases
  • link
failure
  • fast
rise in
  • erred
load
  • high
noise in
  • erred
load
  • la
rge drift
  • ver
time
  • Simulations
coverage: { OSPF-OMP is completely covered. { ISIS-OMP is not implemented at all. { MPLS-OMP LSP deletion is not implemented. { MPLS-OMP link failure is not implemented. { MPLS simulations a re not y et
  • n
the w eb page. { If UUNET simulations cannot b e made available, simula- tions using a complex hyp
  • thetical
top
  • logy
a re needed.
slide-14
SLIDE 14 Summa ry
  • Algo
rithms a re b eing validated through simulations. { Most a re available at http://engr.ans.net/ospf-omp
  • Status:
draft-ietf-ospf-omp-01.txt,ps { Little change to the algo rithms since
  • 00
version. { Substantial imp rovement to the do cument since
  • 00.
{ Optimization
  • f
pa rtial paths needs to b e added. { Another iteration
  • f
the draft is needed. { Comments w
  • uld
b e nice. Implementations nicer.