\nint fa0\/0<\/span><\/span><\/span>
\nip ospf hello-interval <sec><\/span><\/span><\/span>
\nip ospf dead-interval <sec><\/span><\/span><\/span><\/p>\n
sh ip ospf interface<\/span><\/span><\/span><\/p>\n int fa0\/0<\/span><\/span><\/span> -> Hello -> e.g. – 4 times a second, every 250 ms<\/p>\n – Passive interface router ospf 1<\/span><\/span><\/span> sh ip protocols<\/span><\/span><\/span><\/p>\n Manual Neighborship<\/b><\/p>\n – Only allowed on non-broadcast multi-access (NBMA) networks neighbor<\/p>\n OSPF Authentication<\/b><\/p>\n – 3 types -> type 1 – plain text<\/p>\n -> type 2 – MD5<\/p>\n – Configuration -> Area-wide – all routers in the area must be configured<\/p>\n Interface level configuration<\/p>\n – Plain text (type 1) – MD5 (type 2) Area Wide Authentication<\/p>\n Scenario -> Configure area wide authentication on R1 for area 0, but R2 is not configured for authentication, so skip s0\/0 of R1.<\/p>\n R1(config)# router ospf 1<\/span><\/span><\/span> int s0\/1<\/span><\/span><\/span> Interface configuration is preferred over area wide authentication<\/p>\n Virtual-links are a special case with authentication and commonly comes up in the lab<\/p>\n DR \/ BDR Election on multi-access networks<\/b><\/p>\n – One router is elected the DR -> highest router-id<\/p>\n -> any manual router-id config<\/p>\n -> highest loopback address<\/p>\n -> highest physical interface address<\/p>\n – Another router which is second best is elected the BDR<\/p>\n – All routers for a fully adjacent neighborship with the DR and BDR SPF is a point-to-point protocol<\/p>\n – It doesn’t work on multi-access networks<\/p>\n – DR becomes a pseudo node to create a logical point-to-point network<\/p>\n Transit network means you have to go through the pseudo node<\/p>\n R3# sh ip ospf ne<\/span><\/span><\/span>i R2\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2-way \/ DROTHERS<\/p>\n R4\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Full \/ BDR<\/p>\n R5\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Full \/ DR<\/p>\n Changing Priority<\/p>\n int fa0\/0<\/span><\/span><\/span> -> 0 – no participation in election<\/p>\n -> 1 – default priority<\/p>\n OSPF Network Types<\/b><\/p>\n – Depending on the interface OSPF is activated on, it decides some properties to be used -> DR \/ BDR<\/p>\n -> Type of neighborship<\/p>\n 1. Broadcast Multi-access<\/p>\n 2. Point-to-point<\/p>\n 3. Non-broadcast Multi-access (NBMA)<\/p>\n 4. Point-to-multipoint<\/p>\n 5. Point-to-multipoint Non-broadcast<\/p>\n Frame-relay default to NBMA<\/p>\n – When it is setup as a hub and spoke int s0\/0<\/span><\/span><\/span> sh ip ospf database<\/span><\/span><\/span> Link State Update (LSU)<\/b><\/p>\n – A set of LSAs (Link State Advertisements) -> LSA-ID – router-id<\/p>\n -> neighbors connected to a router<\/p>\n -> networks connected to a router<\/p>\n -> LSA 2 – Network LSA<\/p>\n -> LSA-ID – IP address of DR<\/p>\n -> Information about transit network ( DR \/ BDR \/ DROTHERS )<\/p>\n -> Originated by DR<\/p>\n -> LSA 3 – Summary LSA<\/p>\n -> LSA-ID – for every network in the other area<\/p>\n -> Created by ABR<\/p>\n -> Cost to reach network from the ABR<\/p>\n -> LSA 4 – ASBR Summary<\/p>\n -> LSA-ID – router-id of ASBR<\/p>\n -> Contains cost of ABR to reach ASBR<\/p>\n -> LSA 5 – AS-External<\/p>\n -> LSA-ID – external networks<\/p>\n -> Created by ASBR<\/p>\n -> Cost of ASBR to reach external networks<\/p>\n -> LSA 7 – Not-so-stubby-area (NSSA)<\/p>\n -> LSA-ID – external network<\/p>\n -> Created by ASBR<\/p>\n -> Cost of ASBR to reach external networks<\/p>\n sh ip ospf database <LSA type><\/span><\/span><\/span> – network<\/p>\n – summary<\/p>\n – asbr-summary<\/p>\n – as-external<\/p>\n – nsaa-external<\/p>\n OSPF Cost Calculation<\/b><\/p>\n – Cumulative cost of all exit interfaces towards destination<\/p>\n Cost of serial ethernet = 100 \/ 1.544 = 64<\/p>\n Cost of fast ethernet = 100 \/ 100 = 1<\/p>\n Cost of gigabit ethernet = 100 \/ 1000 = 1<\/p>\n Fast ethernet and Gigabit ethernet having the same cost is not a good thing<\/p>\n On the exam, if you see Gigabit ethernet interfaces, you may need to change the formula<\/p>\n router ospf 1<\/span><\/span><\/span> R3# sh ip ospf database route 4.4.4.4<\/span><\/span><\/span> The change cost int s0\/0<\/span><\/span><\/span> int s0\/0<\/span><\/span><\/span> R1 to 50.0.0.0<\/p>\n – Route #1 – R1 -> R2 -> R4 -> 50.0.0.0 = cost of 66<\/p>\n – Route #2 – R1 -> R3 -> R5 -> 50.0.0.0 = cost of 66<\/p>\n Scenario -> Change the cost in this diagram in such a way that R1 goes to 50.0.0.0 by following the route R1 -> R2 -> R3 -> R5 -> 50.0.0.0<\/p>\n When asked a question about traffic engineering, always start at the end OSPF Summarization<\/b><\/p>\n – Can be done on Area Border (ABR)<\/p>\n – Can be done on Domain Border (ASBR) -You cannot summarize within an area R2(config)# router ospf 1<\/span><\/span><\/span> router ospf 1<\/span><\/span><\/span> R3(config)# router ospf 1<\/span><\/span><\/span> Default Route<\/b><\/p>\n router ospf 1<\/span><\/span><\/span> ->without this keyword, the local router needs a default route in the routing table<\/p>\n -> with this keyword, the default route is injected regardless of a default route being represent in the local routing table<\/p>\n -> metric – default is 1<\/p>\n OSPF Filtering<\/b><\/p>\n – Filtering is only possible on Area Borders<\/p>\n router ospf 1<\/span><\/span><\/span><\/p>\n area <number> filter-list prefix <name> in | out<\/span><\/span><\/span><\/p>\n Scenario -> Filter lo0 of R3 from Area 0<\/p>\n R2(config)# ip prefix-list ABC deny 3.3.3.3 255.255.255.255<\/span><\/span><\/span> router ospf 1<\/span><\/span><\/span> It’s preferable to filter out of an area when multiple areas are present<\/p>\n – Filtering coming into an area does not stop the router from entering the database table R1(config)# access-list 1 deny 3.3.3.3<\/span><\/span><\/span> router ospf 1<\/span><\/span><\/span> Not a good method;\u00a0\u00a0 it can cause problems, but will likely come up in the exam<\/p>\n – A static route pointing to NULL0 is much better, but static routes are heavily frowned upon in the exam<\/p>\n Filtering by Distance<\/b><\/p>\n router ospf 1<\/span><\/span><\/span>
\nip ospf dead-interval minimal hello-multiplier <number of hellos><\/span><\/span><\/span>
\n-> dead interval set to 1 sec<\/p>\n
\n-> multicast hello processing is disabled<\/p>\n
\npassive-interface { default | <int> }<\/span><\/span><\/span><\/p>\n
\nrouter ospf 1<\/p>\n
\n-> type 0 – NULL<\/p>\n
\n-> Interface – connected neighbor must be configured<\/p>\n
\nint s0\/0<\/span><\/span><\/span>
\nip ospf authentication<\/span><\/span><\/span>
\nip ospf authentication-key <password><\/span><\/span><\/span><\/p>\n
\nint s0\/0<\/span><\/span><\/span>
\nip ospf authentication<\/span><\/span><\/span>
\nip ospf message-digest-key <id> md5 <password><\/span><\/span><\/span><\/p>\n![\"20140929_194106\"](\"https:\/\/feralpacket.org\/wp-content\/uploads\/2015\/01\/20140929_194106.jpeg\")
<\/a><\/p>\n
\narea 0 authentication<\/span><\/span><\/span>
\n-> all interfaces must now use authentication<\/p>\n
\nip ospf authentication-key <password><\/span><\/span><\/span>
\nint s0\/2<\/span><\/span><\/span>
\nip ospf authentication-key <password><\/span><\/span><\/span>
\nint s0\/0<\/span><\/span><\/span>
\nip ospf authentication NULL<\/span><\/span><\/span><\/p>\n
\n-> highest priority<\/p>\n
\n-> 2-WAY neighborship is formed with all other routers<\/p>\n<\/a><\/p>\n<\/a><\/p>\n
\nR1\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2-way \/ DROTHERS<\/p>\n
\nip ospf priority <number><\/span><\/span><\/span>
\n-> 0 – 255 (higher is better)<\/p>\n
\n-> Timers<\/p>\n<\/a><\/p>\n
\n-> If a spoke is elected DR, the other spokes will not be able to communicate with the DR<\/p>\n
\nip ospf network <options><\/span><\/span><\/span><\/p>\n
\n-> shows database header information<\/p>\n
\n-> LSA 1 – Router LSA<\/p>\n
\n– router<\/p>\n
\nauto-cost reference-bandwidth <Mbps><\/span><\/span><\/span><\/p>\n<\/a><\/p>\n
\n-> shows the cost to R4’s connected network from R4’s point of view<\/p>\n
\n-> bandwidth manipulation<\/p>\n
\nbandwidth 2000<\/span><\/span><\/span><\/p>\n
\nip ospf cost < 1 – 65535 ><\/span><\/span><\/span><\/p>\n<\/a><\/p>\n
\n-> R2’s link to R4 –
\nip ospf cost 3<\/span><\/span><\/span>
\n-> R1’s link to R3 –
\nip ospf cost 67<\/span><\/span><\/span><\/p>\n
\n-> border between routing protocols<\/p>\n
\n-> That would defeat the point of SPF<\/p>\n<\/a><\/p>\n
\narea <source area> range <network> <subnet><\/span><\/span><\/span><\/p>\n
\narea 0 range 10.0.0.0 255.255.252.0<\/span><\/span><\/span><\/p>\n<\/a><\/p>\n
\nredistribute eigrp 1 subnets<\/span><\/span><\/span>
\nsummary-address 192.168.0.0 255.255.254.0<\/span><\/span><\/span><\/p>\n
\ndefault-information originate [always] [router-map <name>] [metric <value>] [metric-type [1|2]]<\/span><\/span><\/span>
\n-> always<\/p>\n<\/a><\/p>\n
\nip prefix-list ABC permit 0.0.0.0 0.0.0.0 le 32<\/span><\/span><\/span><\/p>\n
\narea 0 filter-list prefix ABC in<\/span><\/span><\/span><\/p>\n<\/a><\/p>\n
\n-> it can be filtered and prevented from entering the routing table<\/p>\n<\/a><\/p>\n
\naccess-list 1 permit any<\/span><\/span><\/span><\/p>\n
\ndistribute-list 1 in<\/span><\/span><\/span><\/p>\n
\ndistance 255 <source> <wildcard> <acl><\/span><\/span><\/span><\/p>\n