OSPF LSA type

LSA type 1 – Router LSAs are sent from a router to other routers in the same area. It contains information regarding the routers interfaces in the same area, relevant interfaces IPs, its adjacent routers on those interfaces and sub networks

LSA type 2 – Network LSAs are generated by the DR on a multi access segment, and provides similar information to an LSA type 1 for the multi access segment and subnet which it belongs
LSA type 3 – Network Summary LSAs are generated by ABRs and contain the subnets & costs but omit the topological data from all subnets in one area and sent to another area via the ABR
LSA type 4 -ASBR summary LSAs are from ASBRs and are identical in structure to a type 3 LSA and sent when crossing an AS boundary
LSA type 5 -Are AS external LSAs which are originated by ASBRs and describe external networks
LSA type 6 – Is defined as a Group Membership LSA but not used in Cisco devices
LSA type 7 -NSSA External LSAs are generated by the ASBR in an NSSA area
LSA type 8 – Is defined as a External Attribute LSA but not used in Cisco devices
LSA types 9 to 11 – Defined as Opaque LSAs and are reserved for future expansion

ref.: http://communitystring.com/2008/07/ospf-lsa-types/

Area Type	Type 1 & 2 (within area)	Type 3 (from other areas)	Type 4	Type 5	Type 7
Standard & backbone	Yes	Yes	Yes	Yes	No
Stub	Yes	Yes	No	No	No
Totally stubby	Yes	No	No	No	No
NSSA	Yes	Yes	No	No	Yes
Totally stubby NSSA	Yes	No	No	No	Yes

ref.: https://learningnetwork.cisco.com/docs/DOC-7924

OSPF - Normal, Stub, Totally Stub and NSSA Area Differences

ref.: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094aaa.shtml#definestub

Normal	None
Stub	No Type 5 AS-external LSA allowed
Totally Stub	No Type 3, 4 or 5 LSAs allowed except the default summary route
NSSA	No Type 5 AS-external LSAs allowed, but Type 7 LSAs that convert to Type 5 at the NSSA ABR can traverse
NSSA Totally Stub	No Type 3, 4 or 5 LSAs except the default summary route, but Type 7 LSAs that convert to Type 5 at the NSSA ABR are allowed

more information about LSA type:

http://raycheang.blogspot.com/2012/03/ospf-lsa-type.html

OSPF

1. Hello - Hello packets are used to establish and maintain adjacency with other OSPF routers. The hello protocol is discussed in detail in the next topic.

2. DBD - The Database Description (DBD) packet contains an abbreviated list of the sending router's link-state database and is used by receiving routers to check against the local link-state database.

3. LSR - Receiving routers can then request more information about any entry in the DBD by sending a Link-State Request (LSR).

4. LSU - Link-State Update (LSU) packets are used to reply to LSRs as well as to announce new information. LSUs contain seven different types of Link-State Advertisements (LSAs). LSUs and LSAs are briefly discussed in a later topic.

5. LSAck - When an LSU is received, the router sends a Link-State Acknowledgement (LSAck) to confirm receipt of the LSU.

OSPF router initial procedure

1. Sending Hello packets on all OSPF-enabled interfaces to determine if there are any neighbors on those links. OSPF Hello packets are sent as multicast to an address reserved for ALLSPFRouters at 224.0.0.5 (By default, OSPF Hello packets are sent every 10 seconds on multiaccess and point-to-point segments and every 30 seconds on non-broadcast multiaccess (NBMA) segments (Frame Relay, X.25, ATM). )
   
2. Before two routers can form an OSPF neighbor adjacency, they must agree on three values: Hello interval, Dead interval, and network type.
3. Send Link-state updates (LSUs) to advertise routing information. An LSU packet can contain 11 different types of Link-State Advertisements (LSAs).
•  LSA type: 1    Router LSAs
• type 2             Network LSAs
• type 3 or 4      Summary LSAs
• type 5             Autonomous System Extrenal LSAs
• type 6             Multicast OSPF LSAs
• type 7             Defined for Not-So-Stubby Areas
• type 8             External Attributes LSA for BGP
• type 9,10,11   Opaque LSAs
  
4. Each OSPF router maintains a link-state database containing the LSAs received from all other routers. Once a router has received all of LSAs and built its local link-state database.
   
5. OSPF uses Dijkstra's shortest path first (SPF) algorithm to create an SPF tree. 
6. The SPF tree is then used to populate the IP routing table with the best paths to each network.
   

Eigrp - what happens after network command is issued

Here is EIGRP message

As soon as you configure network command on eigrp, following things happen in the given order:

Step 1. Hellos are sent.

Step 2. Receive Update.

Step 3. Run the dual and install the best route for the network learned in 2nd step.

Step 4. Send update about that interface.

An important observation here is that first of all, the above 4 steps are executed for directly connected networks.

You must be knowing this..i guess..

But notice their order..

Suppose there are two routers R1 and R2 connected via a serial link

Suppose there is a fast ethernet on each of the router R1 and R2..

Let the serial interfaces be named as R1S and R2S.

Let the fast ethernet interfaces be named as R1F and R2F

So R1 and R2 are connected via R1S and R2S...

As soon as u configure the network command, following things happen on Router R1..

a) Hello sent to R1F

b) Received update from R1F about that network

c) Run Dual and calculate the best path with the available data and feasible successor for the network learnt in step b. Enter the successor in routing table.

So you see, although local networks are already in the routing table, yet DUAL recalculates the best path and recreate the routing table with that network ..

d) Send update about network of R1F

"" At this stage ROUTING TABLE IS CREATED ( With one fastethernet network )...although Hellos are YET TO BESENT TO serial interface R1S. """

e) Hello sent to R1S

f) Received update from R1S about that network

g) Run Dual and calculate the best path and feasible successor for the network learnt in step f. Enter the successor in routing table.

h) Send update about network of R1S

After the above steps, neighbour adjancency is established with R2 if all the parameters are okay..

SO IT MEANS HELLOS ARE NOT IMMEDIATELY SENT ON ALL THE APPROPRIATE INTERFACES..

It is sent on one interface and then above 4 steps get executed in the above order.

Then hello is sent on 2nd interface and then again above 4 steps get executed in the given order.

Similar process goes on for the other interfaces that are enabled for receiving and sending EIGRP updates.

So routing table is created (though it is not complete) BEFORE hellos are sent out all the appropriate interfaces.

ref.:https://cisco.hosted.jivesoftware.com/message/5596

RIP Timers

RIP uses four different kinds of timers to regulate its performance:

Route update timer   Sets the interval (typically 30 seconds) between periodic routing updates
in which the router sends a complete copy of its routing table out to all neighbors.

Route invalid timer   Determines the length of time that must elapse (180 seconds) before a
router determines that a route has become invalid. It will come to this conclusion if it hasn’t
heard any updates about a particular route for that period. When that happens, the router will
send out updates to all its neighbors letting them know that the route is invalid.

Holddown timer   This sets the amount of time during which routing information is sup-
pressed. Routes will enter into the holddown state when an update packet is received that indi-
cated the route is unreachable. This continues either until an update packet is received with a
better metric or until the holddown timer expires. The default is 180 seconds.

Route flush timer   Sets the time between a route becoming invalid and its removal from the
routing table (240 seconds). Before it’s removed from the table, the router notifies its neigh-
bors of that route’s impending demise. The value of the route invalid timer must be less than
that of the route flush timer. This gives the router enough time to tell its neighbors about the
invalid route before the local routing table is updated.

ref.: Cisco Certified Network Associate Study Guide

Cisco router password recovery

step 1: press Ctrl+Break once the router boot up

step 2:
rommon 1>confreg 0x2142
rommon 2>reset

======================================================
remark:
0x2000 is boot default ROM software
0x0040 is ignore NVRAM
the last 2 is to specifies default boot file name

Router default register is 0x2102, you can check it by "sh version"