OSPF Open Shortest Path First
OSPF chasto primenyaemyj protokol marshrutizacii vnutri
avtonomnoj sistemy.
Router hranit topologicheskuyu bazu opisyvayushchuyu polnuyu
strukturu seti. Po baze router vychislyaet shortest-path tree, s
soboj v kachestve kornya. Obrashcheniem dereva vychislyaetsya tablica
marshrutizaci. Pri izmeneniii sostoyaniya linkov routery
rassylaet sosedyam Link State Advertise(LSA)-soobshcheniya s
informaciej o sostoyanii linkov. LSA tak zhe rassylayutsya kazhdye
30 minut. Posle polucheniya LSA router perestraivaet
topologicheskuyu bazu.
Konkurenty protokola OSPF
RIP (routed) - ne podderzhivaet setevye maski, rassylaet
polnuyu tablicu routinga kazhdye 30 sek. Schitaet optimal'nost'
puti tol'ko po chislu hopov.
IGRP - podderzhivaet setevye maski, rabotaet po sobytiyu,
hranit "vesa" linkov, ne trebuet bol'shih resursov, no
realizovan tol'ko na CISCO-routerah.
Link-state protokol.
VLSM - Variable Length Subnet Mask. Klassy - otmenyayutsya.
Prostaya shema s setyami klassa A,B,C nedostatochno gibka,
trebuetsya chtoby protokoly routinga umeli podderzhivat' VSML.
OSPF eto delaet.
Raschitan dlya raboty v ierarhicheskih setyah.
Areas - gruppirovka podsetej v "areas" - neperesekayushchiesya
zony.
Umeet summarizovat' routing s pogloshcheniem.
Podderzhivaetsya routerami bol'shinstva proizvoditelej.
OSPF router ID.
LSA - Link State Advertisment.
Hello protocol
Raspredelenie obyazannostej mezhdu routerami v multicast-seti
Types LSAs
Summarizaciya routinga
LSM
Dialekty raznyh proizvoditelej
Poryadkovyj nomer, pod kotorym router izvesten v OSPF.
Ispol'zuetsya pri rabote protokola mezhdu routerami dlya
koordinacii.
Po umolchaniyu - starshij IP-adres na aktivnom interfejse.
LSA - Link State Advertisment
LSA - opoveshchayushchee soobshchenie, posylaetsya routerom na
aktivnyj interfejs. Soderzhit vsyu informaciyu o vyzvannom
izmenenii routinga.
Esli LSA prines izmeneniya, to oni vnosyatsya v
topologicheskuyu bazu, po SFP-algoritmu perestraivaetsya tablica
routinga i LSA rassylaetsya dal'she.
Inache LSA dal'she ne rassylaetsya.
Poslannyj paket rasprostranyaetsya dalee vsemi routerami
(esli v etom est' neobhodimost')
Posylaetsya tol'ko pri izmenenii sostoyaniya linka
A tak zhe posylaetsya kazhdye 30 minut. (Na vsyakij sluchaj)
Primer:
---------------------------------------------------------------
Router# show ip ospf database
OSPF Router with id(192.168.239.66) (Autonomous system 300)
Displaying Router Link States(Area 0.0.0.0)
Link ID ADV Router Age Seq# Checksum Link count
172.18.21.6 172.18.21.6 1731 0x80002CFB 0x69BC 8
172.18.21.5 172.18.21.5 1112 0x800009D2 0xA2B8 5
172.18.1.2 172.18.1.2 1662 0x80000A98 0x4CB6 9
172.18.1.1 172.18.1.1 1115 0x800009B6 0x5F2C 1
172.18.1.5 172.18.1.5 1691 0x80002BC 0x2A1A 5
Displaying Net Link States(Area 0.0.0.0)
Link ID ADV Router Age Seq# Checksum
172.18.1.3 192.20.239.66 1245 0x800000EC 0x82E
Displaying Summary Net Link States(Area 0.0.0.0)
Link ID ADV Router Age Seq# Checksum
172.18.240.0 172.18.241.5 1152 0x80000077 0x7A05
172.18.241.0 172.18.241.5 1152 0x80000070 0xAEB7
172.18.244.0 172.18.241.5 1152 0x80000071 0x95CB
Vyvodit listing s vremenami poslednij obnovlenij LSA
paketov s sosednih routerov.
---------------------------------------------------------------
Point-to-Point - sosed opredelyaetsya odnoznachno - eto
"tot-konec"
Multiaccess - sosedi nahodyatsya po otkliku na Hello protocol
(napr. ethernet, vydelyaetsya Designate Router (za glavnogo)
FDDI)
Nonbroadcast - sosedej pridetsya zadavat' yavno pri
Multiaccess konfiguracii OSPF
(napr. Frame relay,
X.25)
Vydelennye DR routery v Multiaccess-seti
Rassylat' v multicast-seti LSA-soobshcheniya ot kazhdogo k
kazhdomu - slishkom dorogoe udovol'stvie. "Sosedi" vse svoi LSA
shlyut tol'ko vydelennomu Designed Router'u(DR). DR rassylaet
akkumulirovannye LSA vsem "sosedyam".
DR vybiraetsya po protokolu Hello. Hello ispol'zuet
setevye multicast soobshcheniya po 224.0.0.5.
Vybiraetsya tak zhe Backup Designate Routera (BDR) -
zapasnoj. On avtomaticheski zamenit DR esli ot togo ne pridet
ni odnogo LSA dol'she opredelennogo vremeni. Stav DR on
proiniciiruet vybory novogo BDR.
Vnov' vklyuchennyj router otdaet svoj LSA DR'u (tochnee
DR+BDR) posylaya multicast po 224.0.0.6
DR rassylaet svoi LSA vsem "svoim" posylaya multicast po
224.0.0.5
Primer:
---------------------------------------------------------------
Router# debug ip osfp events
Router (config-if)# shutdown
! interfejs "upal"
Listing etoj komandy pokazhet spisok rassylaemyh LSA
Router (config-if)# no shutdown
! interfejs "ozhil"
Listing etoj komandy pokazhet spisok rassylaemyh LSA
---------------------------------------------------------------
Prostranstvo adresov v OSPF organizuesya po ierarhicheskomu
principu, raspadayas' na neperesekayushchiesya area (zony?)
Klassifikaciya OSPF routerov
Area Border Router (ABR) - imeet interfejsy, podklyuchennye
srazu k neskol'kim area. Dlya kazhdogo iz takih interfejsov
vypolnyaet svoyu kopiyu algoritma routinga.
Internal router - vse interfejsy podklyucheny k
setyam, raspolozhennym v odnoj i toj zhe area. Ispolnyaet odnu
kopiyu algoritma routinga.
Backbone router - imeet interfejs k bekbonu
Autonomous System Boundary router - obmenivaetsya
informaciej s routerami, prinadlezhashchimi raznym avtonomnym
sistemam
* Konfigurirovanie OSPF *
Zapusk processa routinga OSPF
---------------------------------------------------------------
Router# router ospf process-id
---------------------------------------------------------------
process-id Vnutrennij nomer - unikal'noe znachenie dlya
kazhdogo processa routinga. OSPF processy na
"druzhestvennyh" routerah zapuskayutsya s odnim i tem zhe
process-id
Opredelit', kakie interfejsy ispolnyayut OSPF
---------------------------------------------------------------
Router# network netaddress wildcard-mask area area-id
---------------------------------------------------------------
netaddress Adres napryamuyu podklyuchennyh setej ili podsetej
wildcard-mask Obrashchennaya maska dlya sravneniya zadannogo adresa
s adresami interfejsov (chtob vyyasnit' - ispolnyat'
li OSPF na dannom interfejse)
area-id Zadaet, kakoj area prinyadlezhat adresa
---------------------------------------------------------------
router ospf 63
network 1.0.0.0 0.255.255.255 area 0
---------------------------------------------------------------
Primer 2. Vnutrennij router
---------------------------------------------------------------
interface e 0
ip address 131.108.25.1 255.255.255.0
interface e 1
ip address 131.108.2.26 255.255.255.0
interface e 2
ip address 131.108.3.7 255.255.255.0
interface loopback 0
ip address 3.3.3.3 255.0.0.0
---------------------------------------------------------------
Variant 1
Razreshaem v OSPF tol'ko perechislennye interfejsy
router ospf 63
network 131.108.25.1 0.0.0.0 area 0
network 131.108.3.7 0.0.0.0 area 0
network 131.108.2.26 0.0.0.0 area 0
Variant 2
Razreshaem v OSPF vse, chto popadet v masku
router ospf 63
network 131.108.0.0 0.0.255.255 area 0
Variant 3
Razreshaem v OSPF vse, v t.ch. adresa na loopback-interfejse
router ospf 63
network 0.0.0.0 255.255.255.255 area 0
Primer 3. Konfigurirovanie Area Border Router
---------------------------------------------------------------
network 131.108.25.1 0.0.0.255 area 0
network 131.108.0.0 0.0.255.255 area 34
---------------------------------------------------------------
V primere interfejsy (e0) i (e1 + e3) "smotryat" v raznye
area. Hotya 131.108.25.1 popadaet vnutr' 131.108.0.0, no
preimushchestvo imeet bolee tochnyj routing.
Tipy Link State Andvertisement
Router LSA
Posylaetsya vnutri-area routerami
Vyzyvayut pereraschet SPF dereva
"O" (OSPF derived router)
Summary LSA
Posylaetsya Area Border routerom
"IA" (Inter Area routes)
---------------------------------------------------------------
Roter# show ip ospf
Routing Process "ospf 201" with ID 192.168.110.200
Supports only single TOS(TOS0) route
It is an area border and autonomous system boundary router
Summary Link update interval is 0:30:00 and the update due in 0:16:26
External Link update interval is 0:30:00 and the update due in 0:16:27
Redistributing External Routes from,
igrp 200 with metric mapped to 2, includes subnets in redistribution
rip with metric mapped to 2
igrp 2 with metric mapped to 100
igrp 32 with metric mapped to 1
Number of areas in this access server is 3
Area 192.168.110.0
Number of interfaces in this area is 1
Area has simple password authentication
SPF algorithm executed 6 times
Area ranges are
Link State Update Interval is 0:30:00 and due in 0:16:55
Link State Age Interval is 0:20:00 and due in 0:06:55
---------------------------------------------------------------
"O" - OSPF derived router (Router LSA)
"IA" - Inter Area routes (Summary LSA)
"E1" - Type-1 External Routes
"E2" - Type-2 External Routes
Metrika tipa E1 sumiruet vnutrennie i vneshnie metriki
Metrika tipa E2 sumiruet tol'ko vneshnie metriki
(t.e. ne uchityvaet metriku pri prohozhdenii
odnoj i toj zhe area
Konfigurirovanie v nonbroadcast setyah
Esli set' ne imeet broadcast'a (napr. frame-relay, X.25),
"sosedej" po OSPF pridetsya zadavat' v yavnom vide
Primer:
---------------------------------------------------------------
router ospf
neighbor 172.16.3.4 priority 1 poll-interval 180
---------------------------------------------------------------
* SUMMARIZACIYA ROUTINGA *
Tablicy routinga dlya B
---------------------------------------------------------------
131.108.4.0 255.255.252.0
131.108.8.0 255.255.252.0
131.108.12.0 255.255.252.0
~~~~~~~~~
131.108.16.0 255.255.252.0
. . .
131.108.28.0 255.255.252.0
~~~~~~~~~
||
\/
131.108.16.0 255.255.240.0
---------------------------------------------------------------
Summarizaciya routinga sokrashchaet kolichestvo strok v tablice
routinga, pri etom rasshiryaetsya (virtual'naya) setevaya maska -
vklyuchayushchaya v sebya nastoyashchie setevye maski.
Summarizaciya routinga mozhet porozhdat' fantomnyj routing
(nesushchestvuyushchih setej)
~~~~~~~~~
131.108.12.0 255.255.252.0
~~~~~~~~~
||
\/
131.108.12.0 255.255.240.0
Pri etom 131.108.8.0 255.255.252.0 vypadaet po takoj setevoj
maske v 0-yu podsetku.
Konfiguraciya summarizacii routinga
---------------------------------------------------------------
Route# area area-id range address mask
---------------------------------------------------------------
---------------------------------------------------------------
router ospf 63
network 1.0.0.0 0.255.255.255 area 0
network 2.0.0.0 0.255.255.255 area 2
area 0 range 1.0.0.0 255.0.0.0
area 2 range 2.0.0.0 255.0.0.0
router ospf 63
network 1.0.0.0 0.255.255.255 area 0
network 3.0.0.0 0.255.255.255 area 3
area 0 range 1.0.0.0 255.0.0.0
area 3 range 3.0.0.0 255.0.0.0
---------------------------------------------------------------
Dlya korrektnoj summarizacii routinga trebuetsya
raspredelenie adresov nepreryvnymi kuskami
---------------------------------------------------------------
Route# show ip protocols
. . .
Routing Protocol is "ospf 109"
Sending updates every ?? seconds, next due in ?? seconds
Invalid after ??? seconds, hold down 280, flushed after 630
. . .
---------------------------------------------------------------
Podderzhka variacij OSPF raznyh proizvoditelej
CISCO-router ----- > non-CISCO-router
---------------------------------------------------------------
Router (config-if)# ip ospf cost cost
---------------------------------------------------------------
Pri vychislenii puti Cisco-routery dlya ocenki stoimosti
interfejsa ispol'zuyut shirinu linka (bandwidth). Realizacii OSPF
drugih proizvoditele mogut ispol'zovat' dlya opredeleniya ceny
drugie algoritmy. Dlya soglasovaniya stoimost' linka v etom
sluchae pridetsya zadavat' vruchnuyu komandoj ip osf cost
* KRATKIJ SPISOK OSPF KOMAND *
area authentication
area virtual-link
default-information originate (OSPF)
default-metric (BGP, EGP, OSPF, and RIP)
ip ospf authentication-key
ip ospf cost
ip ospf dead-interval
ip ospf hello-interval
ip ospf message-digest-key
ip ospf network
ip ospf priority
ip ospf retransmit-interval
ip ospf transmit-delay
ip ospf-name-lookup
match route-type
network area
neighbor (OSPF)
ospf auto-cost-determination
router ospf
redistribute
set metric-type
show ip ospf
show ip ospf border-routers
show ip ospf database
show ip ospf interface
show ip ospf neighbor
show ip ospf virtual-links
Last-modified: Tue, 03 Mar 1998 21:31:29 GMT