CHAPTER 1
EIGRP will usually reconverge within two seconds, sometimes nearly instantaneously.
RIP will not reconverge until its hold-down timer expires after 180 seconds.
IGRP will not reconverge until its hold-down timer expires after 270 seconds.
OSPF will not reconverge for six or seven seconds.
It waits five seconds before it even starts to reconverge to make sure all routers
have heard about a change before it recalculates new routes.
Cisco routers support up to six lowest-cost paths to a destination
in the routing table. IP routing attempts to load share traffic across equal metric paths.
Rip 2, OSPF, IS-IS,EIGRP and BGP4 support VLSM
IGRP, EGP and ripv1 do not support VLSM
Summarization - enables a given routing protocol to minimize ip routing
tables by taking steps to advertise a smaller or lesser IP
Route destination for a large set of subnets or networks.
(Summarization limits or reduces Ip routing tables)
Benifits of Summarization
#1.Reduces Routing Table Sizes
#2.Allows for Network growth
#3.Simplifies routing algorithm recalculation when changes occur
#4.Reduces Requirements for memory and CPU usage on routers Significantly
RIPv2 and EIGRP have Auto Summarization
no auto-summary ( command disables auto summarization )
The routing protocols that automatically summarize on the classful network boundary
are RIPv1, RIPv2, IGRP, and EIGRP.
(conf-if)# ip summary-address eigrp 1 131.108.1.0 255.255.248.0
( this summarizies AS 1 131.108.1.1 - 131.108.1.7
Remember that the bits that are off it will summarizes)
OSPF Has manual Summarization
(config)#router ospf 1
(conf-router)#area 1 range 131.108.1.0 255.255.255.248.0
IP HELPER Address
used to change a broadcast into a more specific destination address
so not all devices must view the IP data.
RFC 1918 RESERVES 10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255 FOR PRIVATE USE
CHAPTER 2.
DEFAULT ADMINISTRATIVE DISTANCE VALUES
#1. Connected interface -- 0
#2. Static route address -- 1
#3. Enhanced IGRP Summary Route -- 5
#4. External BGP -- 20
#5. EIGRP -- 90
#6. IGRP --100
#5. OSPF --110
#6. IS-IS --115
#7. RIP --120
#8. EGP --140
#9. External EIGRP --170
#10. Internal BGP --200
#8. Unknown / Unbelievable --255
Distance Vector Protocols.
RIP broadcasts routing updates of routing tables every 30 sec by default.
RIP can load balance six equal cost paths(four paths is the default)
RIP HOLDOWN 180
RIP FLUSH TIMER 240
RIP 1 no triggerd updates or VLSMS
RIP-2 permits VLSMs and supports triggerd updates
RIP ipx updates every 60 secs default,default packet size is 576 bytes and can contain
up to 50 entries.
IGRP Max Default HOP COUNT 100, Max Configured HOP 255
IGRP ROUTING UPDATES SENT OUT EVERY 90 secs
IGRP FLUSH TIMER IS 630 secs
IGRP HOLD DOWN 280
IGRP performs triggerd updates
Linkstate protocols use SPF or also known as Dijkstra algo.
Ping OutPut Symbols.
! = Each Exclamation point indicates receipt of a reply
. = Each Period indicates the network server timed out while waiting for a reply
U = A destination unreachable error was recieved
C = A congestion experienced packet was recieved
I = user interrrupted test
? = unknown packet type
& = packet lifetime exceeded
CHAPTER 3
The router with the highest priority is elected as
the designated router (DR). If there is a tie,
the router with the highest router ID wins.
OSPF Default COst
* 56-kbps serial link - cost=1785
* T1 - cost=64
* Ethernet - cost=10
* 16-Mbps Token Ring - cost=6
CHAPTER 4 ROUTING PRINCIPLES
ROUTING PROTOCOL METRICS
-------------------------
RIPv1 - HOP COUNT
Ripv2 - HOP COUNT
IGRP - Bandwidth,Delay,Load, Realibility, MTU ( Bandwidth Delay Default )
EIGRP - Bandwidth,Delay,Load, Realibility, MTU ( Bandwidth Delay Default )
OSPF - COST ( Higher Bandwidth Lower Cost )
IS-IS - Cost
SHOW IP ROUTE Explain
----------------------
I - IGRP
R - RIP
O - OSPF
C - Connected
S - STATIC
E - EGP
B - BGP
i - IS-IS
D - EIGRP
CLASSLESS ROUTING PROTOCOLS
----------------------------
Rip 2, OSPF, IS-IS,EIGRP and BGP4 support VLSM
CLASSFULL ROUTING PROTOCOLS
----------------------------
IGRP, EGP and ripv1 do not support VLSM
DISTANCE VECTOR ROUTING LOOP PREVENTION
---------------------------------------
Split Horizon
Poison Reverse
Hold-Down
Triggerd Updates
Aging of routes from the routing table
Count to infinity
ROUTING PROTOCOL UPDATE TIMERS
-------------------------------
CHAPTER 5
OSPF Terms
Database descriptors - DDPs contain lsas which describe the links of ever router in the
neighbors topology (sent during the exchange state)
LSA a packet that contains all relevant information regarding
a routers links and the state of those links.
OSPF Network Topologies
#1. Broadcast Multiaccess - Lan / ethernet network, token ring or FDDI
OSPF sends out multicast traffic. DR and BDR
are elected
#2. Point-To-Point - Serial or when there is only one other router directly connected.
no DR or BDR.
#3. Point to Multipoint - treats the network as a series of point to point circuits
it replicates LSA packets for each circuit. OSPF traffic is sent
as multicast. There is no DR or BDR.uses one ip subnet for all
endpoints on the network.
#4.Non Broadcast Multi Access - Wan clouds x.25 and frame relay are examples of this technology
NBMA uses a fully meshed or partially meshed network.
OSPF sees it as a broadcast network and it will be represented
by one ip subnet.Requires manual configuration of neighbors
and DR && BDR selection
#5 Virtual Links - virtual connection to a remote area that does not have any
connections ro the backbone(area0)
OSPF Configured ROuter - Sends out a small hello packet every 10 secs default
THE HELLO PACKET.
Router ID - 32 bit number. Highest ip on the router is used as the ID.
if loopback configured this will be used even if its not the highest address.
if multiple loopbacks highest is chosen.
Hello/Dead - Dead interval=40 Hello=10 sec / broadcast or multiaccess
Dead interval=120 hello=30 sec / non broadcast
Neighbors - Router id of a neighbor is entered in the neighbor table when a
bidirectional communication is established within the deadrouterinterval.
the communication is established when the router sees itself listed as a
neighbor in the hello packet generated by another router on the same
physical segment.
Area Id - Area ID of the originating router interface.
RouterPriority - priority of the source router interface.the higher priority the higher
likelihood of the router being selected as a DR or BDR.
DR IP add - Address of the existing DR
BDR IP ADD - address of the existing BDR
Auth pass - specifies the authentication type and information. if set the password must
match the password stated on the router.
stub area flag - identifies which type of lsas will be transmitted and accepted.
Adjacent OSPF Neighbors
Adjacency - Formed by two neighbor routers that have exchanged information and have the
same topology table. the databases are syncronized and they both see the same networks
OSPF circulates through a number of states when a router starts running OSPF:
1. Down - the router has not exchanged information with any other router
2. Init - a hello packet is received and added to the router's list of neighbors
3. Two-Way - when the router adds the router to its neighborship database (in broadcast networks, it only proceeds beyond two-way state for connectivity to DR and BDR)
4. DR and BDR election - only on broadcast networks, and only if not already elected
5. Exstart - the DR and BDR exchange adjacencies with each router in the network
6. Exchange - the master and slave routers exchange at least one database description
7. Loading - when link-state requests (LSRs) are sent
8. Full - when all LSRs for a given router are received and the routers are synchronized