1. LSA Types
    1. 1. Router LSA
      1. routers within the area flood type 1 lsa's containing directly connected links
        1. Link Identification:
          1. 1. IP Prefix
          2. 2. Link Type:
          3. Point To Point
          4. Link ID: Neighbor RID
          5. Transit Network
          6. Link ID: IP Address of DR
          7. Stub Network
          8. Link ID: IP Network
          9. Virtual Link
          10. Link ID: Neighbor RID
      2. these lsa's always stay within an area
    2. 2. Network LSA
      1. created for each multi-access network
      2. for broadcast/non-broadcast the DR generates these lsa's
      3. includes connected routers to the multi-access network, the DR, prefix & subnet mask
    3. 3. Summary LSA
      1. created by ABR
      2. flooded into other areas
    4. 4. Summary ASBR LSA
      1. ABR generates
      2. includes RID of the ASBR in the link state ID field
    5. 5. Autonomous System External LSA
      1. generated by the ASBR
      2. contains information about external prefixes redistributed into OSPF
    6. 6. Multicast OSPF LSA
      1. not used anymore
      2. not supported by Cisco
    7. 7. Not So Stubby Area LSA
      1. in NSSA areas Type 5 LSA's are not allowed. Type 7 LSA's are created to get around this to show redestributed prefixes
      2. Created by ABR
    8. 8. External Attribute LSA For BGP
  2. Commands:
    1. sh ip ospf data
      1. shows OSPF LSDB
    2. (under router config) #redistribute connected subnets
      1. redistribute subnets on a router without the network command
    3. (under router config) #area <0-65000> nssa
      1. configure not so stubby area
    4. (under router config) #redistribute <rip,eigrp,bgp> <as #> <subnets>
      1. "subnets" keyword included for addresses that are not classful
      2. redistributes routes from other routing protocols into OSPF
  3. Summarization
    1. impossible to summarize within an area
    2. must configure summarization on a ABR or ASBR
    3. OSPF can only summarize LSA Type 3 and 5
    4. must configure summarization manually
    5. Nothing will change in other areas if an interarea summarization is configured
    6. summary route will only be advertised if you have at least one subnet that is within the summary range
      1. if links to all subnets in the summary fail then the summary is withdrawn
    7. summary route will have the cost of the subnet with the lowest cost that falls within the summary range
    8. ABR that creates a summary route will create a null0 interface to prevent loops
    9. OSPF is classless so any subnet mask can be used for prefixes
    10. Command to summarize on ABR/ASBR:
      1. (under router config) #area <0-65000> range <ip address subnet> <subnet mask>
    11. External Summarization (Type 5 LSA'S)
      1. use "summary address <ip address/mask>" (under router config)
      2. configure on ASBR
  4. OSPF Special Area Types
    1. Stub Area
      1. No ASBR's
      2. No Type 5 external LSA's
      3. must have at least one ABR in area
      4. all routers in area must be configured as stub
      5. Command:
        1. (router config) #area <1-65000> stub
    2. Totally Stub Area
      1. No ASBR's allowed
      2. No Type 3 Summary LSA
      3. No Type 5 external LSA
      4. must have at least one ABR in area
      5. all routers in area must be configured as stub
      6. Commands:
        1. (router config) #area <1-65000> stub no-summary
    3. NSSA
      1. ASBR's allowed
        1. Type 7 LSA's replace Type 5
      2. No Type 5 external LSA's
      3. Default routes must be installed manually on ABR
        1. Commands:
          1. (router-config) #area <1-65000> nssa default-information-originate
      4. Commands:
        1. (router config) #area <1-65000> nssa
    4. Totally Not So Stubby Area
      1. ASBR's allowed
      2. No Type 3 Summary LSA
      3. No Type 5 External LSA
      4. Commands:
        1. (router config) #area <1-65000> nssa no-summary
    5. Special area types are used to insert default routes into an area and replace Type 3 Summary LSA's and Type 5 External LSA's
      1. keeps LSA flooding to a minimum
      2. Smaller LSDB
      3. Less SPF calculations
      4. Smaller routing table
    6. configuring an area as stub blocks ALL Type 5 External LSA's
    7. No ASBR's allowed in stub area
      1. to reach other networks in other areas a default route is setup
  5. OSPF Authentication
    1. Methods:
      1. Plain Text
      2. MD5
    2. Interface Authentication: Plain Text
      1. (router-interface) #ip ospf authentication
      2. (router-interface) #ip ospf authentication-key <key>
    3. Interface Authentication: MD5
      1. (router-interface) #ip ospf message-digest-key <key#> md5 <password>
      2. (router-interface) #ip ospf authentication message-digest
    4. Area Authentication:
      1. Plain Text
        1. (router-config) #area <0-65000> authentication
      2. MD5
        1. (router-config) #area <0-65000> authentication message-digest
    5. Packet Debugging Codes:
      1. Aut:0 = no authentication
      2. Aut:1 = plaintext authentication
      3. Aut:2 = MD5