OSPF LSA-Type 3 Metric Value

[JohnTylerPearce]

I've always noticd in a LSA Type-3, there is a Metric value. What exactly is that used for?

Routing Bit Set on this LSA

  LS age: 721

  Options: (No TOS-capability, DC, Upward)

  LS Type: Summary Links(Network)

  Link State ID: 10.0.0.0 (summary Network Number)

  Advertising Router: 6.6.6.6

  LS Seq Number: 80000003

  Checksum: 0xC646

  Length: 28

  Network Mask: /24

        TOS: 0  Metric: 12

I understand that from an ABR's point of view, when it advertises Type-3 LSA,s into an area, it's distance vector. Which makes sense, since all its saying is "I promise I heard about these networks", which is not a Link State protocol trait

[Jan Hrnko · Accepted solution]

Hi John,

metric value included in LSA3 is the distance between ABR and the destination network.

It is used by other routers in area (to which the LSA3 is flooded) to calculate the best path for that inter-area destination network.

Best path = intra-area distance from router towards ABR + distance from ABR towards destination network (metric in LSA3).

Best regards,

Jan

[JohnTylerPearce]

Thanks Jan, for whatever reason I always forget that.

[Jan Hrnko]

John,

you're welcome. Don't worry, me too - but from now on, whenever one of us forget it, we can find it right here .

Best regards,

Jan