May 8, 2012

CCNP ROUTE - Opaque LSAs

Type 9, 10, 11 (Opaque LSAs) may be used for distributing application-specific information through an OSPF domain.

  • Type 9 LSAs are not flooded beyond the local network or subnetworks.
    • A link-local "opaque" LSA (defined by RFC2370) in OSPFv2 and the Intra-Area-Prefix LSA in OSPFv3. It is the OSPFv3 LSA that contains prefixes for stub and transit networks in the link-state ID.
  • Type 10 LSAs are not flooded beyond the borders of their associated area.
    • An area-local "opaque" LSA (defined by RFC2370). Opaque LSAs contain information which should be flooded by other routers even if the router is not able to understand the extended information itself. Typically type 10 LSAs are used for traffic engineering extensions to OSPF, flooding extra information about links beyond just their metric, such as link bandwidth and color.
  • Type 11 LSAs are not flooded through the AS.
    • An AS "opaque" LSA defined by RFC 5250which is flooded everywhere except stub areas. This is the opaque equivalent of the type 5 external LSA.

CCNP ROUTE - OSPF over NBMA 快速記憶法

第一次學習OSPF的同學遇到NBMA時總會覺得大腦不夠用,怎麼記都很容易搞混,到底什麼時候要設定Neighbor,什麼時候要選擇DR/BDR? (請參考下圖)


我在這邊提供兩個快速記憶法:

  1. 只要是OSPF Mode內含nonbroadcast字串(包含NBMA)皆需手動設定Neighbor
    • 因為不支持broadcast(multicast)無法傳送multicast hello,所以一定要設定Neighbor改用unicast
  2. 只要是OSPF Mode開頭為Point-to-XXX字串皆不須選擇DR or BDR
    • Point-to-XXX常見於WAN的環境,因此沒有DR/BDR這類代表multiaccess broadcast的需求
  3. 除了標準LAN(Broadcast)/WAN(Point-to-Point)之外的OSPF Mode Hello Timer皆為30 secs

希望對各位在學習過程中可以有些幫助!