PRO-TIP: Don't treat this as a long list of items to memorize but rather a checklist of topics to lab up.
Default Behavior
- Won't start unless OSPF can determine a router-id
- Router-id determined:
- Configured router-id
- Highest loopback IP address
- Highest interface IP address
- Every router within an area must have the same OSPF database
- Filtering/Summaries happen at the ABR
- Default Priority = 1, highest priority becomes the DR (where applicable)
- A Priority of "0" means router will NOT participate in DR/BDR elections.
OSPF Network Types
Broadcast
- Default for Ethernet interfaces
- Elects DR/BDR
- Uses Multicast
- Allows more than 2 routers on a link
- Timers: Hello - 10, Dead - 40
Non-Broadcast
- Elects a DR/BDR
- Uses Unicast (neighbor statements)
- Allows more the 2 routers on a link
- Timers: Hello - 30, Dead - 120
Point-to-Point
- Default for Serial and Tunnel interfaces
- Does NOT elect DR/BDR
- Uses Multicast
- Only 2 routers allowed on a link
- Timers: Hello - 10, Dead - 40
Point-to-MultiPoint
- Does NOT elect DR/BDR
- Uses Multicast
- Allows more than 2 routers on a link
- Installs /32 host routes per neighbor
- Timers: Hello - 30, Dead - 120
Point-to-MultiPoint Non-Broadcast
- Does NOT elect DR/BDR
- Uses Unicast (neighbor statements)
- Allows more than 2 routers on a link
- Installs /32 host routes per neighbor
- Timers: Hello - 30, Dead - 120
Loopback
- Default for Loopback interfaces
- When included in OSPF, uses a /32
- To advertise with mask other-than /32, manually set network type to "point-to-point"
LSA Types
LSA Type-1: Router LSA's
- Originated from each router
- Flooded within an area
- Tells the area about all the links participating in OSPF and are associated with that area
LSA Type-2: Network LSA's
- Originated by the DR
- Only DR can originate Type-2 LSA's (If there is no DR their aren't any Type-2's)
- This LSA tells all the routers in an area about all the routers on a shared medium like Ethernet
LSA Type-3: Summary LSA's
- Originated by an ABR
- Carry the destination network prefixes from one area into another
From nonbackbone > backbone
- Connected Routes
- Intra-Area Routes
From backbone > nonbackbone
- Connected Routes
- Intra-Area Routes
- Inter-Area Routes
LSA Type-4: ASBR-Summary LSA's
- Originated by an ABR
- Tells all the other areas about the ASBR
- Tells all the other areas "to get to this Router-ID(ASBR) go through Me(ABR)!"
LSA Type-5: External LSA's
- Originated by an ASBR
- Flooded through out the OSPF domain, except into stubby areas
- Contains the Network prefix and subnet-mask for the external network
LSA Type-7: NSSA External LSA's
- Originated by ASBR
- Exist only in a Not-So-Stubby Area (NSSA)
- Are NOT flooded outside the area they were originated
Area Types
Backbone Area
- Area 0
- Act's as the HUB for all other areas
- Accepts all LSA Types
Normal Area
- All non-stub areas
- Allows LSA's Type: 1, 2, 3, 4, 5 & External Default
Stub Area
- Allows LSA Types: 1, 2, 3 & Summary Default Route ( No External Type-5's )
Totally Stubby Area
- Allows LSA Types: 1, 2 & Summary Default Route
Not-So-Stubby Area (NSSA)
- Allows LSA Types: 1, 2, 3, 7 ( No External Type-5's )
- NSSA's allow redistributing into an area but still maintain it's 'stub area' properties (not allowing External Type-5's)
- Redistributed routes are converted to Type-7 LSA's and advertised throughout the area by the ASBR
- The ABR converts Type-7 LSA's into Type-5's before advertising them into the backbone area.
- LSA Type-7's are only flooded within the area they originate
Totally Not-So-Stubby Area (NSSA)
- Allows LSA Types: 1, 2, 7 & Summary Default Route ( No External Type-5's )
- NO LSA Type-3's
Route Types
- O = Intra-area Route
- O IA = Inter-area Route (Generated by Type-3 LSA's)
- E1 = External Metric Type-1 (Generated by Type-5 LSA's)
- E2 = External Metric Type-2 (Generated by Type-5 LSA's)
- N1 = NSSA Metric Type-1
- N2 = NSSA Metric Type-2
Marvelous and accurate.
ReplyDeleteThank you.
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