1. Introduction to OSPF Route Summary
- ABR 및 ASBR만 OSPF route summary 가능
- ABR은 LSA type 3 route를 summary
- ASBR은 LSA type 5 route를 summary
- juniper는 ASBR 및 ABR에서 LSA type 7 route summary 가능
- summary route의 cost는 specific network address 중 가장 큰 cost 값을 사용
- route summary는 최소한의 specific network address 정보를 수신해야 가능
- ABR에서 network summary 시, specific network가 다운되었을 때, routing loop을 방지하기 위해 summary를 수행한 ABR routing table에 next-hop이 discard(null 0)인 route가 생성
- juniper는 ASBR에서 LSA type 5, type 7 route를 summary 하기 위해 "aggregate route"를 이용하여 "policy-options" 설정이 필요
- juniper는 "aggregate route"를 사용하여 external network summary 시, specific network가 다운되었을 때, routing loop을 방지하기 위해 summary를 수행한 장비의 routing table에 next-hop이 reject(null 0)인 route가 생성
- juniper는 "aggregate route"를 사용하여 external network summary 시, 기본적으로 external metric type 2, metric 0으로 전달
- cisco 및 nokia는 external network summary 시, ASBR routing table에 next-hop이 null 0인 route 미생성
2. OSPF Route Summary Configuration 구성도
1) OSPF Route Summary Configuration 구성도
- 본 글은 LSA type 3, type 5, type 7이 정상적으로 summary되고 summary를 설정한 장비의 routing table에 next-hop이 discard 및 reject인 route가 생성되는지 확인하는 것이 목표
- 실제로 OSPF route summary할 경우가 거의 없으므로 juniper configuration만 확인할 예정
2) 테스트 장비
- Emulator : EVE-NG
- OS : Juniper vMX 23.1R1.8
3. OSPF Route Summary Configuration
1) Interface and OSPF Configuration
더보기
< vMX1 : Interface 및 OSPF 설정 >
set interfaces ge-0/0/1 unit 0 family inet address 1.1.2.1/24
set interfaces lo0 unit 0 family inet address 1.1.1.1/32
set routing-options router-id 1.1.1.1
set protocols ospf area 0.0.0.2 interface lo0.0
set protocols ospf area 0.0.0.2 interface ge-0/0/1.0 interface-type p2p< vMX2 : Interface 및 OSPF 설정 >
set interfaces ge-0/0/0 unit 0 family inet address 1.1.2.2/24
set interfaces ge-0/0/1 unit 0 family inet address 1.2.3.2/24
set interfaces lo0 unit 0 family inet address 2.2.2.2/32
set routing-options router-id 2.2.2.2
set protocols ospf area 0.0.0.0 interface lo0.0
set protocols ospf area 0.0.0.0 interface ge-0/0/1.0 interface-type p2p
set protocols ospf area 0.0.0.2 interface ge-0/0/0.0 interface-type p2p< vMX3 : Interface 및 OSPF 설정 >
set interfaces ge-0/0/0 unit 0 family inet address 1.2.3.3/24
set interfaces lo0 unit 0 family inet address 3.3.3.3/32
set routing-options router-id 3.3.3.3
set protocols ospf area 0.0.0.0 interface lo0.0
set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 interface-type p2proot@vMX2> show ospf neighbor
Address Interface State ID Pri Dead
1.2.3.3 ge-0/0/1.0 Full 3.3.3.3 128 37
1.1.2.1 ge-0/0/0.0 Full 1.1.1.1 128 36
2) NSSA, Redistribution, Passive Configuration
< vMX1 : Redistribution 설정 >
set interfaces ge-0/0/9 unit 0 family inet address 10.1.1.1/24
set interfaces ge-0/0/9 unit 0 family inet address 10.1.2.1/24
set interfaces ge-0/0/9 unit 0 family inet address 10.1.3.1/24
set policy-options policy-statement EXPORT from protocol direct
set policy-options policy-statement EXPORT then accept
set protocols ospf export EXPORT< vMX2 : Passive 설정 >
set interfaces ge-0/0/5 unit 0 family inet address 10.2.1.1/24
set interfaces ge-0/0/6 unit 0 family inet address 10.2.2.1/24
set interfaces ge-0/0/7 unit 0 family inet address 10.2.3.1/24
set protocols ospf area 0.0.0.2 interface ge-0/0/5.0 passive
set protocols ospf area 0.0.0.2 interface ge-0/0/5.0 metric 10
set protocols ospf area 0.0.0.2 interface ge-0/0/6.0 passive
set protocols ospf area 0.0.0.2 interface ge-0/0/6.0 metric 20
set protocols ospf area 0.0.0.2 interface ge-0/0/7.0 passive
set protocols ospf area 0.0.0.2 interface ge-0/0/7.0 metric 30- OSPF route를 summary 하기 위해 네트워크 추가 생성
3) LSA Type 3 Route Summary Configuration
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000004 124 0x22 0xae2e 60
Router *3.3.3.3 3.3.3.3 0x80000003 577 0x22 0xcf06 60
Summary 1.1.1.1 2.2.2.2 0x80000002 124 0x22 0x2708 28
Summary 1.1.2.0 2.2.2.2 0x80000003 124 0x22 0x240a 28
Summary 10.2.1.0 2.2.2.2 0x80000002 43 0x22 0xa13 28
Summary 10.2.2.0 2.2.2.2 0x80000002 43 0x22 0x63ae 28
Summary 10.2.3.0 2.2.2.2 0x80000002 43 0x22 0xbc4a 28
ASBRSum 1.1.1.1 2.2.2.2 0x80000003 43 0x22 0x1716 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.1.0 1.1.1.1 0x80000001 60 0x22 0x4959 36
Extern 10.1.2.0 1.1.1.1 0x80000001 60 0x22 0x3e63 36
Extern 10.1.3.0 1.1.1.1 0x80000001 60 0x22 0x336d 36< vMX2 : LSA Type 3 Route Summary 설정>
set protocols ospf area 0.0.0.2 area-range 10.0.0.0/8- ABR인 vMX2에서 LSA type 3 route를 summary 할 네트워크를 설정
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000004 174 0x22 0xae2e 60
Router *3.3.3.3 3.3.3.3 0x80000003 627 0x22 0xcf06 60
Summary 1.1.1.1 2.2.2.2 0x80000002 174 0x22 0x2708 28
Summary 1.1.2.0 2.2.2.2 0x80000003 174 0x22 0x240a 28
Summary 10.0.0.0 2.2.2.2 0x80000001 12 0x22 0xf715 28
ASBRSum 1.1.1.1 2.2.2.2 0x80000004 12 0x22 0x1517 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.1.0 1.1.1.1 0x80000001 110 0x22 0x4959 36
Extern 10.1.2.0 1.1.1.1 0x80000001 110 0x22 0x3e63 36
Extern 10.1.3.0 1.1.1.1 0x80000001 110 0x22 0x336d 36root@vMX3> show ospf database netsummary extensive
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
~~~ 생략 ~~~
Summary 10.0.0.0 2.2.2.2 0x80000001 25 0x22 0xf715 28
mask 255.0.0.0
Topology default (ID 0) -> Metric: 30
Aging timer 00:59:35
Installed 00:00:24 ago, expires in 00:59:35
Last changed 00:00:24 ago, Change count: 1- LSA type 3 route는 설정한 network로 summary되었지만 해당 명령어로 LSA Type 5 route는 summary 불가
- LSA type 3 route summary 시, metric은 specific network 중에 가장 큰 metric 값으로 구성
root@vMX2> show route 10.0.0.0
inet.0: 18 destinations, 18 routes (18 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.0/8 *[OSPF/10] 00:00:34, metric 16777215
Discardroot@vMX3> show route 10.0.0.0
inet.0: 11 destinations, 11 routes (11 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.0/8 *[OSPF/10] 00:00:22, metric 31
> to 1.2.3.2 via ge-0/0/0.0- ABR에서 network summary 시, specific network가 다운되었을 때, routing loop을 방지하기 위해 summary를 수행한 ABR routing table에 next-hop이 discard(null 0)인 route가 생성
root@vMX2> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *2.2.2.2 2.2.2.2 0x80000004 349 0x22 0xae2e 60
Router 3.3.3.3 3.3.3.3 0x80000003 804 0x22 0xcf06 60
Summary *1.1.1.1 2.2.2.2 0x80000002 349 0x22 0x2708 28
Summary *1.1.2.0 2.2.2.2 0x80000003 349 0x22 0x240a 28
Summary *10.0.0.0 2.2.2.2 0x80000001 187 0x22 0xf715 28
ASBRSum *1.1.1.1 2.2.2.2 0x80000004 187 0x22 0x1517 28
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 1.1.1.1 1.1.1.1 0x80000004 285 0x22 0x9e7 60
Router *2.2.2.2 2.2.2.2 0x80000003 268 0x22 0x9dcd 84
Summary *1.2.3.0 2.2.2.2 0x80000001 349 0x22 0x111d 28
Summary *2.2.2.2 2.2.2.2 0x80000001 349 0x22 0xf03c 28
Summary *3.3.3.3 2.2.2.2 0x80000001 349 0x22 0xcc5b 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.1.0 1.1.1.1 0x80000001 285 0x22 0x4959 36
Extern 10.1.2.0 1.1.1.1 0x80000001 285 0x22 0x3e63 36
Extern 10.1.3.0 1.1.1.1 0x80000001 285 0x22 0x336d 36
4) LSA Type 5 Route Summary Configuration
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000004 379 0x22 0xae2e 60
Router *3.3.3.3 3.3.3.3 0x80000003 832 0x22 0xcf06 60
Summary 1.1.1.1 2.2.2.2 0x80000002 379 0x22 0x2708 28
Summary 1.1.2.0 2.2.2.2 0x80000003 379 0x22 0x240a 28
Summary 10.0.0.0 2.2.2.2 0x80000001 217 0x22 0xf715 28
ASBRSum 1.1.1.1 2.2.2.2 0x80000004 217 0x22 0x1517 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.1.0 1.1.1.1 0x80000001 315 0x22 0x4959 36
Extern 10.1.2.0 1.1.1.1 0x80000001 315 0x22 0x3e63 36
Extern 10.1.3.0 1.1.1.1 0x80000001 315 0x22 0x336d 36< vMX1 : LSA Type 5 Route Summary 설정>
set routing-options aggregate route 10.1.0.0/16
set policy-options prefix-list DROP 10.1.1.0/24
set policy-options prefix-list DROP 10.1.2.0/24
set policy-options prefix-list DROP 10.1.3.0/24
set policy-options policy-statement EXPORT term 5 from prefix-list DROP
set policy-options policy-statement EXPORT term 5 then reject
set policy-options policy-statement EXPORT term 10 from protocol direct
set policy-options policy-statement EXPORT term 10 then accept
set policy-options policy-statement EXPORT term 15 from protocol aggregate
set policy-options policy-statement EXPORT term 15 then accept- ASBR인 vMX1에서 LSA type 5 route를 summary 할 네트워크를 설정
- ASBR에서 기존에 재분배하던 network(10.1.1.0/24 ~ 10.1.3.0/24)를 더 이상 광고하지 않고 direct와 aggregate만 재분배하도록 policy-optios을 구성
- juniper는 aggregate route를 자체 프로토콜로 간주
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000004 1433 0x22 0xae2e 60
Router *3.3.3.3 3.3.3.3 0x80000003 1886 0x22 0xcf06 60
Summary 1.1.1.1 2.2.2.2 0x80000002 1433 0x22 0x2708 28
Summary 1.1.2.0 2.2.2.2 0x80000004 788 0x22 0x220b 28
Summary 10.0.0.0 2.2.2.2 0x80000001 1271 0x22 0xf715 28
ASBRSum 1.1.1.1 2.2.2.2 0x80000004 1271 0x22 0x1517 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.0.0 1.1.1.1 0x80000001 1009 0x22 0x544f 36root@vMX3> show ospf database external extensive
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.0.0 1.1.1.1 0x80000001 1021 0x22 0x544f 36
mask 255.255.0.0
Topology default (ID 0)
Type: 2, Metric: 0, Fwd addr: 0.0.0.0, Tag: 0.0.0.0
Aging timer 00:42:59
Installed 00:16:59 ago, expires in 00:42:59
Last changed 00:16:59 ago, Change count: 1- LSA type 5 route가 설정한 network로 summary
- "aggregate route"를 사용하여 external network summary 시, 기본적으로 external metric type 2, metric 0으로 전달
root@vMX1> show route 10.1.0.0
inet.0: 17 destinations, 17 routes (17 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.1.0.0/16 *[Aggregate/130] 00:18:45
Rejectroot@vMX3> show route 10.1.0.0
inet.0: 9 destinations, 9 routes (9 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.1.0.0/16 *[OSPF/150] 00:18:52, metric 0, tag 0
> to 1.2.3.2 via ge-0/0/0.0- "aggregate route"를 사용하여 external network summary 시, specific network가 다운되었을 때, routing loop을 방지하기 위해 summary를 수행한 장비의 routing table에 next-hop이 reject(null 0)인 route가 생성
root@vMX1> show ospf database
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *1.1.1.1 1.1.1.1 0x80000003 686 0x22 0xbe6 60
Router 2.2.2.2 2.2.2.2 0x80000002 684 0x22 0x9fcc 84
Summary 1.2.3.0 2.2.2.2 0x80000002 687 0x22 0xf1e 28
Summary 2.2.2.2 2.2.2.2 0x80000002 186 0x22 0xee3d 28
Summary 3.3.3.3 2.2.2.2 0x80000001 677 0x22 0xcc5b 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern *10.1.0.0 1.1.1.1 0x80000001 691 0x22 0x544f 36
5) LSA Type 7 Route Summary in ASBR Configuration
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000005 39 0x22 0xac2f 60
Router *3.3.3.3 3.3.3.3 0x80000003 2352 0x22 0xcf06 60
Summary 1.1.1.1 2.2.2.2 0x80000003 371 0x22 0x2509 28
Summary 1.1.2.0 2.2.2.2 0x80000004 1254 0x22 0x220b 28
Summary 10.0.0.0 2.2.2.2 0x80000001 1737 0x22 0xf715 28
ASBRSum 1.1.1.1 2.2.2.2 0x80000004 1737 0x22 0x1517 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.0.0 1.1.1.1 0x80000001 1475 0x22 0x544f 36< vMX1 : NSSA 설정 >
set protocols ospf area 0.0.0.2 nssa< vMX2 : NSSA 설정 >
set protocols ospf area 0.0.0.2 nssa- area 2를 NSSA로 구성
- 이전에 LSA type 5 route summary 진행 시, 설정한 policy-options이 존재하므로 추가적인 설정은 불필요
root@vMX2> show ospf database area 2
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 1.1.1.1 1.1.1.1 0x80000003 202 0x20 0x29ca 60
Router *2.2.2.2 2.2.2.2 0x80000002 231 0x20 0xc3a8 84
Summary *1.2.3.0 2.2.2.2 0x80000002 233 0x20 0x2d02 28
Summary *2.2.2.2 2.2.2.2 0x80000002 233 0x20 0xd21 28
Summary *3.3.3.3 2.2.2.2 0x80000001 215 0x20 0xea3f 28
NSSA 10.1.0.0 1.1.1.1 0x80000001 242 0x28 0x1087 36
~~~ 생략 ~~~root@vMX2> show ospf database area 2 nssa extensive
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
NSSA 10.1.0.0 1.1.1.1 0x80000001 299 0x28 0x1087 36
mask 255.255.0.0
Topology default (ID 0)
Type: 2, Metric: 0, Fwd addr: 1.1.1.1, Tag: 0.0.0.0
Aging timer 00:55:01
Installed 00:04:48 ago, expires in 00:55:01
Last changed 00:04:48 ago, Change count: 1- LSA type 7 route는 설정한 network로 summary
- "aggregate route"를 사용하여 external network summary 시, 기본적으로 external metric type 2, metric 0으로 전달
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000003 149 0x22 0xb625 60
Router *3.3.3.3 3.3.3.3 0x80000003 132 0x22 0xcf06 60
Summary 1.1.1.1 2.2.2.2 0x80000001 179 0x22 0x2907 28
Summary 1.1.2.0 2.2.2.2 0x80000002 184 0x22 0x2609 28
Summary 10.0.0.0 2.2.2.2 0x80000001 184 0x22 0xf715 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.0.0 2.2.2.2 0x80000001 179 0x22 0x6833 36- NSSA ABR이 LSA type 7 → type 5로 변경하므로 area 0에서 10.1.0.0 네트워크의 advertising router는 ABR인 vMX2
root@vMX1> show route 10.1.0.0
inet.0: 17 destinations, 17 routes (17 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.1.0.0/16 *[Aggregate/130] 00:36:35
Rejectroot@vMX2> show route 10.1.0.0
inet.0: 16 destinations, 16 routes (16 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.1.0.0/16 *[OSPF/150] 00:06:04, metric 0, tag 0
> to 1.1.2.1 via ge-0/0/0.0root@vMX3> show route 10.1.0.0
inet.0: 9 destinations, 9 routes (9 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.1.0.0/16 *[OSPF/150] 00:05:58, metric 0, tag 0
> to 1.2.3.2 via ge-0/0/0.0- "aggregate route"를 사용하여 external network summary 시, specific network가 다운되었을 때, routing loop을 방지하기 위해 summary를 수행한 장비의 routing table에 next-hop이 reject(null 0)인 route가 생성
root@vMX1> show ospf database
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *1.1.1.1 1.1.1.1 0x80000006 84 0x20 0x23cd 60
Router 2.2.2.2 2.2.2.2 0x80000004 82 0x20 0xbfaa 84
Summary 1.2.3.0 2.2.2.2 0x80000002 90 0x20 0x2d02 28
Summary 2.2.2.2 2.2.2.2 0x80000002 90 0x20 0xd21 28
Summary 3.3.3.3 2.2.2.2 0x80000002 80 0x20 0xe840 28
NSSA *10.1.0.0 1.1.1.1 0x80000001 436 0x28 0x1087 36
6) LSA Type 7 Route Summary in ABR Configuration
< vMX2 : LSA Type 3 Route Summary 설정 제거 >
delete protocols ospf area 0.0.0.2 area-range 10.0.0.0/8- LSA type 3 route summary를 진행하기 위해 설정한 명령어를 제거
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000005 141 0x22 0xb227 60
Router *3.3.3.3 3.3.3.3 0x80000004 2600 0x22 0xcd07 60
Summary 1.1.1.1 2.2.2.2 0x80000003 1232 0x22 0x2509 28
Summary 1.1.2.0 2.2.2.2 0x80000004 2053 0x22 0x220b 28
Summary 10.2.1.0 2.2.2.2 0x80000002 2854 0x22 0xa13 28
Summary 10.2.2.0 2.2.2.2 0x80000002 2582 0x22 0x63ae 28
Summary 10.2.3.0 2.2.2.2 0x80000002 2310 0x22 0xbc4a 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.1.0.0 2.2.2.2 0x80000003 959 0x22 0x6435 36< vMX2 : LSA Type 7 Summary Route 설정 >
set protocols ospf area 0.0.0.2 nssa area-range 10.0.0.0/8- ABR인 vMX2에서 LSA type 7 route를 summary 할 네트워크를 설정
root@vMX3> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 2.2.2.2 2.2.2.2 0x80000005 263 0x22 0xb227 60
Router *3.3.3.3 3.3.3.3 0x80000004 2722 0x22 0xcd07 60
Summary 1.1.1.1 2.2.2.2 0x80000003 1354 0x22 0x2509 28
Summary 1.1.2.0 2.2.2.2 0x80000004 2175 0x22 0x220b 28
Summary 10.2.1.0 2.2.2.2 0x80000002 2976 0x22 0xa13 28
Summary 10.2.2.0 2.2.2.2 0x80000002 2704 0x22 0x63ae 28
Summary 10.2.3.0 2.2.2.2 0x80000002 2432 0x22 0xbc4a 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.0.0.0 2.2.2.2 0x80000001 43 0x22 0x4c53 36root@vMX3> show ospf database external extensive
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.0.0.0 2.2.2.2 0x80000001 56 0x22 0x4c53 36
mask 255.0.0.0
Topology default (ID 0)
Type: 2, Metric: 1, Fwd addr: 0.0.0.0, Tag: 0.0.0.0
Aging timer 00:59:04
Installed 00:00:55 ago, expires in 00:59:04
Last changed 00:00:55 ago, Change count: 1- LSA type 7 route는 설정한 network로 summary
- "aggregate route"를 사용하여 external network summary 시, 기본적으로 external metric type 2, metric 0으로 전달
- 10.0.0.0/8에 대한 metric이 1인 이유는 "ABR인 vMX2에서 ASBR까지 도달하는데 필요한 cost + ASBR에서 destination networkd address까지 도달하는데 필요한 cost"
root@vMX2> show route 10.0.0.0
inet.0: 16 destinations, 16 routes (16 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.0/8 *[OSPF/150] 00:03:58, metric 16777215, tag 0
Discardroot@vMX3> show route 10.0.0.0
inet.0: 11 destinations, 11 routes (11 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.0/8 *[OSPF/150] 00:04:13, metric 1, tag 0
> to 1.2.3.2 via ge-0/0/0.0- ABR에서 network summary 시, specific network가 다운되었을 때, routing loop을 방지하기 위해 summary를 수행한 ABR routing table에 next-hop이 discard(null 0)인 route가 생성
root@vMX2> show ospf database
OSPF database, Area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *2.2.2.2 2.2.2.2 0x80000003 293 0x22 0xb625 60
Router 3.3.3.3 3.3.3.3 0x80000003 292 0x22 0xcf06 60
Summary *1.1.1.1 2.2.2.2 0x80000001 318 0x22 0x2907 28
Summary *1.1.2.0 2.2.2.2 0x80000002 328 0x22 0x2609 28
Summary *10.2.1.0 2.2.2.2 0x80000001 163 0x22 0xc12 28
Summary *10.2.2.0 2.2.2.2 0x80000001 163 0x22 0x65ad 28
Summary *10.2.3.0 2.2.2.2 0x80000001 163 0x22 0xbe49 28
OSPF database, Area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 1.1.1.1 1.1.1.1 0x80000006 324 0x20 0x23cd 60
Router *2.2.2.2 2.2.2.2 0x80000004 320 0x20 0xbfaa 84
Summary *1.2.3.0 2.2.2.2 0x80000002 328 0x20 0x2d02 28
Summary *2.2.2.2 2.2.2.2 0x80000002 328 0x20 0xd21 28
Summary *3.3.3.3 2.2.2.2 0x80000002 318 0x20 0xe840 28
NSSA 10.1.0.0 1.1.1.1 0x80000001 676 0x28 0x1087 36
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern *10.0.0.0 2.2.2.2 0x80000001 115 0x22 0x4c53 36
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