OSPF commands Flashcards
how to configure RID
en- conf t- router ospf 1- router-id 192.168.255.254(ip-addr)
how to configure loop back address for routers
en-conf t- int loop 0- ip addr 192.196.255.254 (ipaddr)
how to show all ospf info (what does it all show)
sh ip protocol
- show Royer ID
loopback adds
connected ip’s in which aread
how to show neighbouring ospf
sh ip ospf neighbor
How to configure routes to connected networks
en-conf t- router ospf 1 - network 10.1.1.0 0.0.0.3 area 0
network 10.1.1.0 0.0.0.254 area 0
(network network-address wildcard-ask area area-id)
-ospf area is a group of routers that share link state info
What is all part of the OSPF packet heacder
- Router ID
- Area id
- type of code for ospf packet type
What is part of the IP packet header
-source ip addr, destination ip addr, protocol field set to 89
OSPF packet types (5)
LAP
OSPF interface priority command
what does that priority ave to be to ensure it is not a DR?
in config- if- ip ospf priority (0-255)
0- not able to be dr or bdr
1 deafult value
higher priority= DR
what is OSPF costs
used to determine best route
cost based on bandwidth- 10*8/ bandwidth
Router ID determined in the following order
- uses ip addr configured with the ospf router-id command
- if none configured- router chooses highest ip of any loopback interface
-if none- router chooses highest ctive ip addr of physical interfaces
(use sh ip protocol to see details)
5 important ospf route sources and administractive distance
Connected - 0
Static - 1
ospf - 110
rip - 120
Hello packets help to do what?
What is a DR
& BDR
Hello protocol packets contain info used to elect DR + BDR
DR- Designated router- responsable to update all other ospf routers
bdr- takes over is DR fails
** point to point links never have a DR****
Hello packet does what?
- discovers neighbours and builds adjacencies between them
b4- 2 routers can be adjacent they must have same values for : - Hello interval, dead interval and Network type
-HI_multicast=( 224.0.0.5) sent ever 30s
DI- default is 4x hello time
Database description (DBD) does?
checks database synchronization b/w routers
Link-state request (LSR)
Requests specific link state records from router to router
Link0state Update (LSU)
sends specifically requested link state records
Link state acknowledgement (LSAck)
acknowledges other packet types
The solution to LSA flooding is DR& DDR by?
routers are elected to send and receive LSA
- DRothers send LSA via multicast 244.0.0.6 to DR&BDR
- DR forwards LSA via multicast addr 244.0.0.5 to all other routers
What is adjacency?
relationship b/w 2 routers that permit direct exchange of router updates
only shared routing info to adjacent neighbours
Designated router
elected when OSPF routers are connected to the same broadcast network to minimize the number of adjacent networks & t publicize received routing info on a broadcast network or link
- elected the highest priority router
- all routers on the same network have synced routing tables
Neighborship database
list of ospf routers where hello packets are sent
router id + state maintained on each router in db
topological database
contains info from all the LSA Packets
computes the shortest path
how is Router ID - RID configured
the ip addr used to identify the router
- cisco chooses RID by using highest ip add of loopback interfaces
if none then the highest ip of a physical interface
neighbours
2 or more routers on a common network
must have same configurations: area id: stub area flag, hello and dead intervals
what is a Link
Network or router interface assigned to any given network
will have up or down state and ip addr
OSPF’s best features
- allows doe the creation of areas
- minimizes routing update traffic
- flexible, versatile, scalable
- supports vlsm/cidr
- offers an unlimited hopcount
- open + support multivendor deployment
OSPF helps to
- confine network instability to single areas
- reduce overhead
- speeds up convergence
OSPF must have?
- area 0 - the backbone
- Area border router (ABR)- router that connects other areas to the backbone
Autonomous system boundary router- connecting multiple autonomous systems together
Link State Advertisement LSA
OSPF data packet containing link state and routing info
ospf router exchanges LSA packets to adjacent routers
OSPF area
- groups of networks and routers
- routers in same area share area id
- area id associated w/ specific interfaces on router
- area id can help scalability
Broadcast/ multicast
allo multiple devices to connect or access same network
DR & BDR must be assigned
Non Broadcast multi access (NBMA)
- this type of network allows multi-access without broadcast ability
Point to mutipoint
network topology made up of a series of connection b/w single interface on one router and multiple destination router
OSPF operations (3)
- neighbor + adjacent initialization
_ LSA flooding
_SPF tree calculations
