Figyelte már valaki az LSA-knál a következő bejegyzést?
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 259
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
A magyarázatára kiolvastam az internetet, de nem találtam választ. Se cisco.com-on, se CiscoPress könyvekből, még a bibliának tartott Routing TCP/IP vol. I. is csak ennyit mond róla:
One line you will notice in Example 8-11and in several subsequent LSA displays is the statement “Routing Bit Set on this LSA.” The routing bit is not a part of the LSA itself; it is an internal maintenance bit used by IOS indicating that the route to the destination advertised by this LSA is valid. So when you see “Routing Bit Set on this LSA,” it means that the route to this destination is in the routing table.
Nekem ebből nem volt egyértelmű. Megjegyzem, sokaknak nem. INE, IPexpert, Cisco Learning Network, stb. fórumokon igazi válasz nélkül maradt a kérdés.
Feltettem az itcafe CCNA/CCNP/CCIE topicban, és crok-tól kaptam egy hasznos választ, átmásolom:
Legegyszerűbben így mondanám el:
Alaphelyzet: R1 Fa0/0<=>Fa0/0 R2
R1(config)#do sh run | s router|prefix|^int.*Fa.*0/0
interface FastEthernet0/0
ip address 10.0.0.1 255.255.255.0
duplex auto
speed auto
router ospf 1
network 10.0.0.0 0.0.0.255 area 0
R2(config)#do sh run | s router|prefix|^int.*Fa.*0/0
interface FastEthernet0/0
ip address 10.0.0.2 255.255.255.0
duplex auto
speed auto
router ospf 1
network 10.0.0.0 0.0.0.255 area 0
Ekkor ezt teszed:
R2
router ospf 1
redistribute static subnets
ip route 0.0.0.0 0.0.0.0 10.0.0.1
..akkor R1 megkapja a default route LSA-t, de nincs routing bit:
R1#sh ip ospf data external 0.0.0.0
OSPF Router with ID (10.0.0.1) (Process ID 1)
Type-5 AS External Link States
LS age: 8
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 10.0.0.2
LS Seq Number: 80000005
Checksum: 0xA3EA
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 10
Forward Address: 10.0.0.1
External Route Tag: 1
Azért nincs, mert az LSA-ban levő route nem tehető be a routing
táblába (saját maga lenne a next hop..).
Ám ha ezt teszem:
R2
router ospf 1
redistribute static subnets
no ip route 0.0.0.0 0.0.0.0 10.0.0.1
ip route 0.0.0.0 0.0.0.0 10.0.0.3
Akkor R1 megkapja az LSA-t és boldogan teszi be a routing bitet:
a route betehető a routing táblába (a next hop connected hálóban van).
R1#sh ip ospf data external 0.0.0.0
OSPF Router with ID (10.0.0.1) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 3
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 10.0.0.2
LS Seq Number: 80000001
Checksum: 0xC7C8
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 10
Forward Address: 10.0.0.3
External Route Tag: 1
Egyszóval: ha az OSFP processz szerint a route bekerülhetne a routing
táblába mert szabály szerint bekerülhet (“sanity check”) akkor megérdemli
a routing bit-et, így ezzel az LSA-val számol az SPF algoritmus. Ebbe a
szabályban még nincs benne az, hogy valamilyen eszközzel manupuláljuk
az LSA-kból a route-ok bekerülését a routing táblába (pl distribute-list), csak
a nyilvánvalóan OSPF-ben részt nem vehető LSA-kat szűrjük (mint a példa:
olyan LSA, amiben saját magunk vagyunk a next hop egy hálózathoz (ami
még csak nem is connected, teljesen ismeretlen számunkra..) ).
FIXME de én így tudom.
Ebből már azt hiszem értem, de ki kellett próbálnom. 3 routerrel csináltam, íme a topológia:
R1-en belehirdetem a default route-t az Area0-ba.
R1(config)#ip route 0.0.0.0 0.0.0.0 Lo1 R1(config)#router ospf 1 R1(config-router)#default-information originate R1(config-router)#^Z R1#
Nézzük, mit látunk a route táblában a többi routeren.
R2#sh ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is 10.0.12.1 to network 0.0.0.0 1.0.0.0/24 is subnetted, 1 subnets O 1.1.1.0 [110/11] via 10.0.12.1, 00:00:48, FastEthernet0/0 2.0.0.0/24 is subnetted, 1 subnets C 2.2.2.0 is directly connected, Loopback0 3.0.0.0/24 is subnetted, 1 subnets O 3.3.3.0 [110/11] via 10.0.23.3, 00:00:38, FastEthernet0/1 10.0.0.0/24 is subnetted, 2 subnets C 10.0.12.0 is directly connected, FastEthernet0/0 C 10.0.23.0 is directly connected, FastEthernet0/1 O*E2 0.0.0.0/0 [110/1] via 10.0.12.1, 00:00:51, FastEthernet0/0 R3#sh ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is 10.0.23.2 to network 0.0.0.0 1.0.0.0/24 is subnetted, 1 subnets O 1.1.1.0 [110/21] via 10.0.23.2, 00:01:01, FastEthernet0/0 2.0.0.0/24 is subnetted, 1 subnets O 2.2.2.0 [110/11] via 10.0.23.2, 00:01:01, FastEthernet0/0 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 10.0.0.0/24 is subnetted, 3 subnets O 10.0.12.0 [110/20] via 10.0.23.2, 00:01:01, FastEthernet0/0 C 10.10.10.0 is directly connected, Loopback1 C 10.0.23.0 is directly connected, FastEthernet0/0 O*E2 0.0.0.0/0 [110/1] via 10.0.23.2, 00:01:04, FastEthernet0/0
Ahogy várható volt, E2 route-ként ott van a default. Nézzük a database-t.
R1#sh ip ospf data ex 0.0.0.0 OSPF Router with ID (1.1.1.1) (Process ID 1) Type-5 AS External Link States LS age: 243 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x1D91 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1 R2#sh ip ospf data ex 0.0.0.0 OSPF Router with ID (2.2.2.2) (Process ID 1) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 259 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x1D91 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1 R3#sh ip ospf data ex 0.0.0.0 OSPF Router with ID (3.3.3.3) (Process ID 1) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 274 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x1D91 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1
R1-en nem tud bekerülni a route táblába OSPF-ből a route, ezért nincs routing bit. R2-n és R3-n van, hiszen R1-től kapják meg.
Csavarjunk rajta: hirdessünk be egy default-ot R3-n is, nézzük, mi történik.
R3(config)#ip route 0.0.0.0 0.0.0.0 Lo1 R3(config)#router ospf 1 R3(config-router)#default-inf origi R3(config-router)#^Z R3#
R1 és R3 nem tesz be a RIB-be default route-t. A lényeg, hogy ilyen esetben az OSPF database-ben ott van mindkét default route T5-ként, de a RIB-be nem kerülnek be. Mivel R1 R3-tól is hallja a route-t, nem csak saját magától, ezért a routing bit ott van.
R1#sh ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is 0.0.0.0 to network 0.0.0.0 1.0.0.0/24 is subnetted, 1 subnets C 1.1.1.0 is directly connected, Loopback0 2.0.0.0/24 is subnetted, 1 subnets O 2.2.2.0 [110/11] via 10.0.12.2, 00:06:11, FastEthernet0/0 3.0.0.0/24 is subnetted, 1 subnets O 3.3.3.0 [110/21] via 10.0.12.2, 00:06:01, FastEthernet0/0 8.0.0.0/24 is subnetted, 1 subnets C 8.8.8.0 is directly connected, Loopback1 10.0.0.0/24 is subnetted, 2 subnets C 10.0.12.0 is directly connected, FastEthernet0/0 O 10.0.23.0 [110/20] via 10.0.12.2, 00:06:04, FastEthernet0/0 S* 0.0.0.0/0 is directly connected, Loopback1 R1#sh ip ospf data ex 0.0.0.0 OSPF Router with ID (1.1.1.1) (Process ID 1) Type-5 AS External Link States LS age: 550 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x1D91 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1 Routing Bit Set on this LSA LS age: 82 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 3.3.3.3 LS Seq Number: 80000001 Checksum: 0xE0C5 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1
R2-n eddigi feltételezésünk szerint equal cost-tal látszódnia kell a default route-knak a RIB-ben, ennek megfelelően kell lennie routing bitnek.
R2#sh ip ospf data ex 0.0.0.0 OSPF Router with ID (2.2.2.2) (Process ID 1) Type-5 AS External Link States Routing Bit Set on this LSA LS age: 735 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x1D91 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1 Routing Bit Set on this LSA LS age: 266 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 3.3.3.3 LS Seq Number: 80000001 Checksum: 0xE0C5 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1
Ez így is van, equal cost, mindkét LSA-ra routing bit.
Na és mi van ha R3-on E1-gyel hirdetem be, ami ugye mindig preferált E2 felett, tekintet nélkül a costra? Feltételezhető, hogy kellene lennie routing bit-nek, hiszen bekerülhet a route táblába.
R2#sh ip route Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is 10.0.23.3 to network 0.0.0.0 1.0.0.0/24 is subnetted, 1 subnets O 1.1.1.0 [110/11] via 10.0.12.1, 00:22:03, FastEthernet0/0 2.0.0.0/24 is subnetted, 1 subnets C 2.2.2.0 is directly connected, Loopback0 3.0.0.0/24 is subnetted, 1 subnets O 3.3.3.0 [110/11] via 10.0.23.3, 00:21:53, FastEthernet0/1 10.0.0.0/24 is subnetted, 2 subnets C 10.0.12.0 is directly connected, FastEthernet0/0 C 10.0.23.0 is directly connected, FastEthernet0/1 O*E1 0.0.0.0/0 [110/11] via 10.0.23.3, 00:00:10, FastEthernet0/1 R2#sh ip ospf data ex 0.0.0.0 OSPF Router with ID (2.2.2.2) (Process ID 1) Type-5 AS External Link States LS age: 394 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x1D91 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1 Routing Bit Set on this LSA LS age: 20 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 3.3.3.3 LS Seq Number: 80000002 Checksum: 0x5BCA Length: 36 Network Mask: /0 Metric Type: 1 (Comparable directly to link state metric) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 1 R2#
Tehát a routing bit azt jelzi, hogy a candidate route-k közül mi kerül be a RIB-be. Ha ugyanaz az út más costtal/type-pal szerepel, a routing bit a legjobbat választja ki (vagy equal).
Nézzük T3 LSA-ra. Ehhez kicsit átalakítottam a topológiát, csináltam egy Area1-t, és visszaállítottam a default-information originate-t az eredeti állapotára.
Most ugyebár R2 ABR lett, így R1-en és R3-n látnunk kell IA route-kat.
R1#sh ip route ospf 2.0.0.0/24 is subnetted, 1 subnets O IA 2.2.2.0 [110/11] via 10.0.12.2, 00:01:25, FastEthernet0/0 3.0.0.0/24 is subnetted, 1 subnets O IA 3.3.3.0 [110/21] via 10.0.12.2, 00:01:25, FastEthernet0/0 10.0.0.0/24 is subnetted, 2 subnets O IA 10.0.23.0 [110/20] via 10.0.12.2, 00:01:25, FastEthernet0/0 R3#sh ip route ospf 1.0.0.0/24 is subnetted, 1 subnets O IA 1.1.1.0 [110/21] via 10.0.23.2, 00:01:56, FastEthernet0/0 2.0.0.0/24 is subnetted, 1 subnets O 2.2.2.0 [110/11] via 10.0.23.2, 00:31:08, FastEthernet0/0 10.0.0.0/24 is subnetted, 3 subnets O IA 10.0.12.0 [110/20] via 10.0.23.2, 00:02:37, FastEthernet0/0
Mivel R2 ABR, ezért ő hirdeti a T3 LSA-kat. Tehát eddigi feltételezésünk szerint R2 ospf database-ben a T3 LSA-khoz nincs routing bit, R1-n és R3-n pedig van. Remélem hasznos volt a bejegyzés. Köszi szépen crok!
R2#sh ip ospf data sum OSPF Router with ID (2.2.2.2) (Process ID 1) Summary Net Link States (Area 0) LS age: 212 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 1.1.1.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x978F Length: 28 Network Mask: /24 TOS: 0 Metric: 11 LS age: 252 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 10.0.12.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0xAA6A Length: 28 Network Mask: /24 TOS: 0 Metric: 10 Summary Net Link States (Area 1) LS age: 258 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 2.2.2.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0xF1F Length: 28 Network Mask: /24 TOS: 0 Metric: 1 LS age: 260 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 3.3.3.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x4FD1 Length: 28 Network Mask: /24 TOS: 0 Metric: 11 LS age: 262 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 10.0.23.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x31D8 Length: 28 Network Mask: /24 TOS: 0 Metric: 10 R1#sh ip ospf data sum OSPF Router with ID (1.1.1.1) (Process ID 1) Summary Net Link States (Area 1) Routing Bit Set on this LSA LS age: 293 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 2.2.2.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0xF1F Length: 28 Network Mask: /24 TOS: 0 Metric: 1 Routing Bit Set on this LSA LS age: 293 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 3.3.3.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x4FD1 Length: 28 Network Mask: /24 TOS: 0 Metric: 11 Routing Bit Set on this LSA LS age: 294 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 10.0.23.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x31D8 Length: 28 Network Mask: /24 TOS: 0 Metric: 10 R3#sh ip ospf data sum OSPF Router with ID (3.3.3.3) (Process ID 1) Summary Net Link States (Area 0) Routing Bit Set on this LSA LS age: 227 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 1.1.1.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x978F Length: 28 Network Mask: /24 TOS: 0 Metric: 11 Routing Bit Set on this LSA LS age: 267 Options: (No TOS-capability, DC, Upward) LS Type: Summary Links(Network) Link State ID: 10.0.12.0 (summary Network Number) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0xAA6A Length: 28 Network Mask: /24 TOS: 0 Metric: 10
