I always like the powerpoint way ... i love it ... i was going through the internetwork expert blog today and found excellent article by mr.scott morris on some general trouble shooting techniques that can drive you insane if not observed ... i have made a power point ... its publicly available in their site if you want to visit it .. you can always do it on
Video 3 of the ospf lab has been released and it is based on ospf virtual link concept..... please feel free to see the topology and also some of the important points in the word doc which is also available ...
In order to make sure that spf is executed properly , area 0 is used as reference point for all other areas in the network
Hence all other areas must have a direct adjacency to area 0
So, the discontiguos area should be connceted to area 0 thorugh any transit area attached to it , through virtual links
Hence , after the configuration the entire set of ospf databases will be synced and full connectivity will be esatblished
DOC:
To define ospf virtual link, use the area virtual-link command in router
Usage Guidelines :
In ospf , all areas must be connected to a backbone router .If the connection to backbone is lost it can be repaired using virtual-links
For a virtual link to be properly configured , each virtual link neighbor must include transit area id and the corresponding virtual link neighbor router id
video 3 has been done and it is on eigrp convegence timers over frame relay ... a word document has also been attached for the reference of topology and points ...
All of the basic ip addressing and frame relay mappings are done and are not included in the video ... the word doc presents you with the topology and some of the important points
I dint wanted to sell the videos even for 5$ but i thought of buying few routers and switches for the switching labs ... but its against my self .. so decided that i would be giving my work to any one who requires for free ... i got 4 paid requests from 4 of the friends .. but i would returning the money back to them tonight .... hence from here on please feel free to download labs and word docs for free .. and if you like you and you have something to throw you can always consider me ... ;)
Also looking for some good team members who can study with me and share some work with me .. it's not impossible to do all the word docs and videos but it would be much easier if there is 'team' / 'we' rather than 'me'
The ospf network type loopback is a special case for loopback interfaces
Network type loopback is the default network type on loopback interfaces , and is not normally configurable with ospf network command
The loopback network type treats the interface as stub host and injects the ip address of the interface as host route into the ospf domain regardless of the actual subnet mask of the interface
setting the ospf network type to point-to-point disables this treatment and advertise the ip address of the interface with the subnet mask configured on that interface
ospf network type point-to-multipoint non-broadcast is similar to the network type point-to-multipoint except that ospf packets are sent as unicast instead of multicast
ospf network type point-to-multipoint , point-to-multipoint non-broadcast does not support the DR/BDR election, and possesses the same next-hop behaviour
hence layer 2 to layer 3 can be between directly connected devices on nbma network and that ip routing will be used to communicate between devices that are not adjacent to layer 2
ospf network type ponit-to-multipoint does not support DR and BDR election
point-to-multipoint sends hello packets to the multicast address 224.0.0.5
point-to-multipoint must be manually configured at the interface level using the command "ip ospf network point-to-multipoint"
There is a difference between point-to-multipoint and the other two broadcast and non-broadcast with the next-hop resolution on a nbma media .
ospf network type point-to-multipoint treats the network as a collection of point-to-point links instead of one broadcast network
In broadcast and non-broadcast , ospf does not deal with layer 2 topology and may not relate it with layer 3 network .
ospf network types broadcast and non-broadcast , next hop values are not modified when updates are sent on nbma
This implies the device on nbma cloud requires layer 3 to layer 2 resolution for any endpoint injecting into the network.
In ospf network type point-to-multipoint , next hop values are changed to the address of directly connceted neighbor when they are advertised across the NBMA cloud.
Routers on NBMA network only need layer 3 to layer 2 resolution for directly connected neighbors when running ospf network point-to-multipoint
ospf network type point-to-multipoint advertises the endpoints of the point-to-multipoint network as host routes instead of actual network itself
The default ospf network type for a multipoint frame relay interface is non-broadcast
The ospf network type non-broadcast generates unicast hello packets and like the broadcast network type supports the DR/BDR election
Hello packets are of unicast type so neighbours must be manually configured with neighbour statement under ospf process
DR in ospf is responsible for distributing lsa to other devices on the segement and hence dr must have a direct layer two connectivity to all devices on the segment
In hub-and-spoke NBMA networks , this implies that hub and only hub should be the DR because hub is the only device which has direct layer two connectivity] to all devices on the network
Commands
show ip ospf neigh show ip ospf inter show ip route
OSPF network statement uses a wildcard mask to identify which interface or interfaces are running the protocol.
The network statement determines which link-state area an interface belong to .
The wildcard mask of the network statement works like the wildcard mask option of an IP access-list , where '0' indicates to check the particular bit position, binary one indicates to ignore the particular bit position
Wild card mask doesnot relate to the IP subnet mask of an interface . It is simply used to determine which interface/interfaces belong to the area of ospf process .
When multiple network statements are configured with overlapping matches , as in the above case , the most specific network statement determines which are the interface will exist in .
commands used :
show ip ospf int
show ip ospf int brief
show ip ospf int | in (Loopback [0-9] | Area)
DOC CD / command reference
NETWORK AREA :
To define the interface on which ospf runs and to define the area id for thos interfaces , use the "network area" command in router confi mode .
wildcard-mask :
ip-address-type mask that include "dont care" bits . Area-id :
Area that is to be associated with ospf address range . It can be specified as either a decimal value or an "IP ADDRESS".
if you intend to associate areas with IP subnets , you can specify a subnet address as the value of the area-id argument. Usage Guidelines:
Using the wildcard-mask argument allows you to define one or multiple interfaces to be associated with a specific ospf area using a single command
For ospf to operate on the interface , the primary address of the interface must be covered by the network area command.
If the network area command covers only the secondary address, it will not enable ospf over that interface
IOS evaluation sequence :
The wildcard-mask argument is logically 'OR' ed with the interface IP address
The wildcard-mask argument is logically 'OR' ed with the ip-address argument in the network command
The software compares the two resulting values. If they match ospf is enabled on the associated interface and this interface is attached to the ospf area specified