OSPF – NSSA LSA Type7-5 Translator Election

Forsätter nöta OSPF-labbar från GNS3 Vault. 🙂

ospfnssa7to5telect

GOAL:

  • All IP addresses have been preconfigured for you.
  • Configure OSPF Area 0.
  • Configure OSPF Area 1 as NSSA.
  • Redistribute the loopback0 interface on router Sam into OSPF Area 1.
  • Ensure router Tron is the router performing the translation from LSA Type 7 to Type 5 into area 0

Konfig:

Skippar all grundkonfig då det är väldigt basic. Använde redistribute connected för att få in 4.4.4.4/24-nätet in i OSPF.

Kontrollerar vi OSPF-databasen kan vi ses att det just nu är Quorra som utför Type 7->5 translations.

Kevin#sh ip ospf database external
OSPF Router with ID (192.168.13.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
 LS age: 53
 Options: (No TOS-capability, DC)
 LS Type: AS External Link
 Link State ID: 4.4.4.0 (External Network Number )
 Advertising Router: 192.168.34.3
 LS Seq Number: 80000001
 Checksum: 0x6E08
 Length: 36
 Network Mask: /24
 Metric Type: 2 (Larger than any link state path)
 TOS: 0
 Metric: 20
 Forward Address: 192.168.34.4
 External Route Tag: 0

Hur kommer då detta sig? Om vi kontrollerar OSPF-databasen för både Quorra & Tron ser vi följande:

Quorra

Quorra#sh ip ospf database nssa-external
OSPF Router with ID (192.168.34.3) (Process ID 1)
Type-7 AS External Link States (Area 1)
Routing Bit Set on this LSA
 LS age: 1079
 Options: (No TOS-capability, Type 7/5 translation, DC)
 LS Type: AS External Link
 Link State ID: 4.4.4.0 (External Network Number )
 Advertising Router: 4.4.4.4
 LS Seq Number: 80000001
 Checksum: 0x6E7C
 Length: 36
 Network Mask: /24
 Metric Type: 2 (Larger than any link state path)
 TOS: 0
 Metric: 20
 Forward Address: 192.168.34.4
 External Route Tag: 0

Tron

Tron#sh ip ospf database nssa-external
OSPF Router with ID (192.168.24.2) (Process ID 1)
Type-7 AS External Link States (Area 1)
LS age: 1120
 Options: (No TOS-capability, Type 7/5 translation, DC)
 LS Type: AS External Link
 Link State ID: 4.4.4.0 (External Network Number )
 Advertising Router: 4.4.4.4
 LS Seq Number: 80000001
 Checksum: 0x6E7C
 Length: 36
 Network Mask: /24
 Metric Type: 2 (Larger than any link state path)
 TOS: 0
 Metric: 20
 Forward Address: 192.168.34.4
 External Route Tag: 0

Så båda routrarna tar emot 4.4.4.0/24-nätet med information att de ska utföra Type 7 -> 5 translation. Kontrollerar vi istället databasen för Type-5 ser vi att endast Quorra som annonserar detta.

Quorra

Quorra#sh ip ospf database external
OSPF Router with ID (192.168.34.3) (Process ID 1)
Type-5 AS External Link States
LS age: 1252
 Options: (No TOS-capability, DC)
 LS Type: AS External Link
 Link State ID: 4.4.4.0 (External Network Number )
 Advertising Router: 192.168.34.3
 LS Seq Number: 80000001
 Checksum: 0x6E08
 Length: 36
 Network Mask: /24
 Metric Type: 2 (Larger than any link state path)
 TOS: 0
 Metric: 20
 Forward Address: 192.168.34.4
 External Route Tag: 0

Tron

Tron#sh ip ospf database external
OSPF Router with ID (192.168.24.2) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
 LS age: 1316
 Options: (No TOS-capability, DC)
 LS Type: AS External Link
 Link State ID: 4.4.4.0 (External Network Number )
 Advertising Router: 192.168.34.3
 LS Seq Number: 80000001
 Checksum: 0x6E08
 Length: 36
 Network Mask: /24
 Metric Type: 2 (Larger than any link state path)
 TOS: 0
 Metric: 20
 Forward Address: 192.168.34.4
 External Route Tag: 0

Varför? Lite efterforskning visade att Ciscos IOS ej har något stöd för att definiera translator direkt i OSPF-processen utan använder sig istället av högst Router-ID. När Tron tar emot LSA Type 5-annonseringen från Quorra som har ett högre RID “flushade” den bort sin egen Type-5 LSA och började använda Quorras istället.

Vill vi ändra Translator måste vi således ändra Router-ID.

Tron(config)#int lo0
Tron(config-if)#ip add 10.10.10.10 255.255.255.255
Tron(config-if)#router ospf 1
Tron(config-router)#router-id 10.10.10.10
Reload or use "clear ip ospf process" command, for this to take effect
Tron(config-router)#do clear ip ospf process
Reset ALL OSPF processes? [no]: yes
Quorra(config)#int lo0
Quorra(config-if)#ip add 9.9.9.9 255.255.255.255
Quorra(config-if)#router ospf 1
Quorra(config-router)#router-id 9.9.9.9
Reload or use "clear ip ospf process" command, for this to take effect
Quorra(config-router)#do clear ip ospf process
Reset ALL OSPF processes? [no]: yes

Kollar vi återigen i Kevin nu kan vi se att Tron har tagit över som Type 7-5 Translator pga ett högre RID. 🙂

Kevin#sh ip ospf database external
OSPF Router with ID (192.168.13.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
 LS age: 11
 Options: (No TOS-capability, DC)
 LS Type: AS External Link
 Link State ID: 4.4.4.0 (External Network Number )
 Advertising Router: 10.10.10.10
 LS Seq Number: 80000001
 Checksum: 0x4E8E
 Length: 36
 Network Mask: /24
 Metric Type: 2 (Larger than any link state path)
 TOS: 0
 Metric: 20
 Forward Address: 192.168.34.4
 External Route Tag: 0

Sweet!

Lämna ett svar

Din e-postadress kommer inte publiceras.