Tag Archives: OSPF

OSPF Process in Packet Tracer

January 01, 2012   Bogdan   No comments

When clearing the OSPF process in Packet Tracer instead of using the command clear ip ospf process, because it is not supported by Packet Tracer, save your config using copy ru sta and then reload, wait for the router to reload and the use sh ip o n.

And be patient because the DR election will take more time in Packet Tracer than in real life.

Read More

OSPF Network Types

January 01, 2012   Bogdan   No comments
  • Non-Broadcast (NBMA) – RFC Standard
  • Point-to-Multipoint – RFC Standard
  • Point-to-Point – CISCO Proprietary
  • Broadcast – CISCO Proprietary (you don’t have to statically configure the neighbs)
  • Point-to-Multipoint, Non-Broadcast – CISCO Proprietary (same as P-M, but you have to statically configure the neighbs)
Read More

OSPF in Single Area

January 01, 2012   Bogdan   No comments

A router is a DR until it is rebooted.

Default OSPF net type for

  • ethernet interface – broadcast
  • serial interface – non broadcast
Read More

OSPF in Multi Areas

January 01, 2012   Bogdan   No comments

Internal Router – all interfaces are confined in the same area
ABR – Area Border Router – one interface in Area 0 (backbone) and another one in nonbackbone area
ASBR – Autonomous System Boundary Router – A router that connects to outside world

LSA Types

  1. Type 1 – O – R link LSA – flooded into an area
  2. Type 2 – O – net link LSA – flooded to whole area
  3. Type 3 – O IA – net summary link LSA – generated by ABR – sent between areas
  4. Type 4 – O IA – AS external ASBR summary link LSA – sent from ABR to ASBR
  5. Type 5 – [O E1|O E2] – external link LSA – flooded throught the AS by ASBRs
  6. Type 7 – NSSA external LSA – by ASBR residing in NSSA

How to remember what type is used by ABR or ASBR ?

  • ABR – 3 letters => LSA Type 3
  • ASBR – 4 letters => LSA Type 4

and the other you know them.

Areas

  • Ordinary or Standard Area – this area connects to backbone
  • Stub Area
    • NO EXT SUMMARY Routes = NO Type 5 LSAs
    • use of default route
    • used in Hub-and-Spoke design
  • Totally Stubby Area (or Total Stub Area)
    • NO SUMMARY LSAs and NO EXT SUMMARY Routes = NO 3,4,5
    • use of default route (network is 0.0.0.0)
    • totally Cisco shop
  • NSSA
    • used when conn to ISPs or when redi is reqed
    • NO 4 or 5 LSA, YES for LSA 7
    • @NSSA ABR LSA 7 is translated in LSA 5
    • RFC 1587 “The OSPF NSSA Option”
  • Backbone Area (Area 0)
    • can propagate all LSAs except LSA 7

Limitations

  • 50 Rs per area;
  • 60 Neighbs per R;
  • 3 areas per R;
  • a R may NOT be a DR or BDR for more than 1 LAN.

STUB and Totally Stubby Areas limitations

  • NO EXT routes are allowed;
  • NO virtual links are allowed;
  • NO redi is allowed;
  • NO ASBR Rs are allowed;
  • the area is NOT the backbone area;
  • All Rs are configed to be STUB Rs.

Commands
default-information originate //+ use of a default route
area range //only on ABRs
summary-address //only on ASBRs

//ASBR performs route redi

I kinda understood what is all about with ABR or ASBR, LSA Types, NSSA, stub and stuff. But it will take me some OSPF configs to understand how it works.

Read More
Stop ACTAStop censorship