LSA 5和LSA 7的区别

LSA 5 和LSA 7的区别

LSA 5 和LSA 7的区别

To provide the ability of carrying external routes originated in the NSSA, a new LSA type was defined, Type 7 LSA.  It has the structure and semantics of a Type 5 (External) LSA, witha two differences:

1.Type 7 LSAs can be originated and propagated within the NSSA, they do not cross area borders like Type 5 LSAs do.
2.Type 5 LSAs are not supported in NSSA; they can be neither originated nor propagated in NSSA. 

Translation of Type 7 to Type 5 LSA at the ABR

An ASBR in a NSSA injects its external routes as Type 7 LSAs (The NSSA does not support Type 5 Externals).  The ABR can (optionally) translate those to regular Type 5 LSAs and inject them into the backbone as Type 5 Externals.  At this point the these LSAs are indistinguishable from other Type 5 LSAs that may have come from other source.  As shown on the figure below, these Type 5 LSAs, along with those from other sources, are flooded on all other non-stub areas.

When the NSSA is connected to the backbone via more than one ABR, the ABR with the highest Router ID is selected to perform the Type 7 à Type 5 translation.  If that ABR fails, the ABR with next-highest Router ID is selected.

TYPE 7-->TYPE 5

应该举一个例子,把show ip ospf data里面的信息显示出来啦~
这个是在nssa区域上的abr上show的数据库信息

r2#sh ip ospf data

OSPF Router with ID ( 2.2.2 .2) (Process ID 1)                 Router Link States (Area 0) Link ID         ADV Router      Age         Seq#       Checksum Link count 1.1.1 .1         1.1.1.1         1247        0x80000006 0xAFDD   3 2.2.2.2         2.2.2.2         437         0x80000003 0x3668   2                 Summary Net Link States (Area 0) Link ID         ADV Router      Age         Seq#       Checksum 3.3.3 .3         1.1.1.1         1473        0x80000001 0x6D7E  4.4.4.4         2.2.2.2         674         0x80000001 0x 21C 2  4.4.4.4         151.1.1.1       1440        0x80000001 0xF35D  5.5.5.5         2.2.2.2         232         0x80000001 0xD441  5.5.5.5         151.1.1.1       1397        0x80000001 0xA7DB  192.168.13.0    1.1.1.1         1639        0x80000001 0xACD5  192.168.24.0    2.2.2.2         988         0x80000004 0xF61   192.168.24.0    151.1.1.1       1435        0x80000004 0xE1FB  192.168.25.0    2.2.2.2         236         0x80000007 0xDFC2  192.168.25.0    151.1.1.1       1401        0x80000003 0xBA59                  Router Link States (Area 1) Link ID         ADV Router      Age         Seq#       Checksum Link count 2.2.2 .2         2.2.2.2         684         0x80000008 0x4435   2 4.4.4.4         4.4.4.4         679         0x80000009 0x4FFE   3                 Summary Net Link States (Area 1) Link ID         ADV Router      Age         Seq#       Checksum 0.0.0 .0         2.2.2.2         812         0x80000002 0x 73C 1  3.3.3.3         151.1.1.1       1474        0x80000001 0xA470  5.5.5.5         151.1.1.1       1398        0x80000001 0xA7DB  192.168.13.0    151.1.1.1       1541        0x80000001 0xE 3C 7  192.168.25.0    151.1.1.1       1408        0x80000001 0xBE57                  Router Link States (Area 3) Link ID         ADV Router      Age         Seq#       Checksum Link count 2.2.2 .2         2.2.2.2         245         0x80000005 0xAF54   1 5.5.5.5         5.5.5.5         241         0x80000008 0x 15AC    2                 Net Link States (Area 3) Link ID         ADV Router      Age         Seq#       Checksum 192.168.25.2    2.2.2 .2         245         0x80000001 0x6E1D                  Summary Net Link States (Area 3) Link ID         ADV Router      Age         Seq#       Checksum 1.1.1 .1         2.2.2.2         440         0x80000002 0x 4F 99  3.3.3.3         2.2.2.2         440         0x80000002 0x752B  3.3.3.3         151.1.1.1       1475        0x80000001 0xA470  4.4.4.4         2.2.2.2         440         0x80000002 0xC418  4.4.4.4         151.1.1.1       1441        0x80000001 0xF35D  192.168.12.0    2.2.2.2         440         0x80000005 0x373E  192.168.13.0    2.2.2.2         440         0x80000002 0xB482  192.168.13.0    151.1.1.1       1573        0x80000001 0xE 3C 7  192.168.24.0    2.2.2.2         440         0x80000005 0xB2B6  192.168.24.0    151.1.1.1       1436        0x80000004 0xE1FB                  Type-7 AS External Link States (Area 3) Link ID         ADV Router      Age         Seq#       Checksum Tag 25.25.24.0      5.5.5 .5         159         0x80000001 0x7CA4   0 55.55.55.0      5.5.5.5         238         0x80000003 0x5468   0                 Type-5 AS External Link States Link ID         ADV Router      Age         Seq#       Checksum Tag 25.25.24.0      2.2.2 .2         160         0x80000001 0x6BCB   0 55.55.55.0      2.2.2.2         234         0x80000001 0x478D   0

注：在工程里面,通常为了减少路由表的深度,我们经常要在ABR上抑止LSA7到LSA5的转换,在以前有个小窍门,现在12.0 ios以后,直接就有命令可以抑止了。