OSPF doubt

lAwBoY

Hi all, anyone can exlpain what to type when using

network command during ospf.

when do they sometimes use the exact ip address of the interface and some use the network id to take part in the ospf.

johnnynodough

Im no expert on OSPF/EIGRP, but here is what I have taken from using wildcard masks with these RPs. Lets say your router has three interfaces, 10.1.2.1, 10.1.3.1, and 10.1.4.1. You can make all three interfaces particpate in the exchange of routing information with one fell swoop command, 10.0.0.0 0.255.255.255. But you can use the three individual commands, to remove any ambiguity as to which interfaces are exchanging router updates, by using the three interface commands 10.1.2.1 0.0.0.0, etc.

Another example would be if you had three interfaces on a router, ips 10.1.2.1, 10.1.3.1 and 10.1.4.1, and you dont want 10.1.4.1 included in the routing updates. If you used the 10.0.0.0 0.255.255.255 net command then that 10.1.4.1 interface would participate in routing. So individual net commands would eliminate that. You could also issue a 10.1.0.0 0.0.3.255 net command, and it would only put the 10.1.2.1 and 10.1.3.1 interfaces in the routing exchanges.

lAwBoY

johnnynodough wrote:

Im no expert on OSPF/EIGRP, but here is what I have taken from using wildcard masks with these RPs. Lets say your router has three interfaces, 10.1.2.1, 10.1.3.1, and 10.1.4.1. You can make all three interfaces particpate in the exchange of routing information with one fell swoop command, 10.0.0.0 0.255.255.255. But you can use the three individual commands, to remove any ambiguity as to which interfaces are exchanging router updates, by using the three interface commands 10.1.2.1 0.0.0.0, etc.

Another example would be if you had three interfaces on a router, ips 10.1.2.1, 10.1.3.1 and 10.1.4.1, and you dont want 10.1.4.1 included in the routing updates. If you used the 10.0.0.0 0.255.255.255 net command then that 10.1.4.1 interface would participate in routing. So individual net commands would eliminate that. You could also issue a 10.1.0.0 0.0.3.255 net command, and it would only put the 10.1.2.1 and 10.1.3.1 interfaces in the routing exchanges.

thanks.. so it mean that i can just enter in the exctal ip address of the interface of the router to ensure that it is exchanging router update with other router right?

so that mean if i got 3 network
10.2.1.4 /30 ip address of e0 is 10.2.1.5
10.3.8.0 /12 ip address of s1 is 10.3.8.1
10.1.0.0 /8 ip address of s2 is 10.1.0.1

and i want all interface to take part in exhanging router update, i can just enter

router ospf 2
network 10.2.1.5 0.0.0.0 area 0
network 10.3.8.1 0.0.0.0 area 0
network 10.1.0.1 0.0.0.0 area 0

---

can i do this as well

router ospf 2
network 10.2.1.4 0.0.0.3 area 0
network 10.3.8.0 0.0.7.255 area 0
network 10.1.0.0 0.255.255.255 area 0

does the two above perform the same result?

QUIX0TIC

router ospf 2
network 10.2.1.5 0.0.0.0 area 0
network 10.3.8.1 0.0.0.0 area 0
network 10.1.0.1 0.0.0.0 area 0

---

can i do this as well?

You can do this and it is a common practice in the field. But, I dont know if this will work to pass the test. Usually, in CCNA... they are looking for the reverse mask answer.

router ospf 2
network 10.2.1.4 0.0.0.3 area 0
network 10.3.8.0 0.0.7.255 area 0 I think you meant to put 0.15.255.255 since it is a /12 network.
network 10.1.0.0 0.255.255.255 area 0

does the two above perform the same result?
They will both have the same result but the later one just adds so many other adxs that may not be wanted or needed. You can usually lower the number down since they are asking for three interfaces. But since they are from 3 differnet networks... it would be appropriate.[/b]

lAwBoY

so which method am i suppose to use during exam

QUIX0TIC

I personally think it is the reverse mask wildcard that is the "more correct" answer. But, this question has been asked multiple times and I am personally sticking with the reverse mask. Its worked for me so far. Ill be taking the test pretty soon... in a couple of weeks or so and if I get a similar question... I can tell you then.

lAwBoY

QUIX0TIC wrote:

I personally think it is the reverse mask wildcard that is the "more correct" answer. But, this question has been asked multiple times and I am personally sticking with the reverse mask. Its worked for me so far. Ill be taking the test pretty soon... in a couple of weeks or so and if I get a similar question... I can tell you then.

Reverse mask meaning ???

thanks bro... let me noe when u take the exam...

johnnynodough

Im going to ask my channel partner training administrator at Cisco, if anyone should know it should be him.

There was a reply by Darkuser in another thread stating that the interface address and fully wild mask was the correct answer, so Im not sure either. Most CCNA books I have read taught the reverse mask, but I dont care for that approach. On the CCO they use the interface address and fully wild mask, but this is just a associate level test.

It also may not matter, as long as it works, of course that is dangerously assuming that Vue and promertics sims are that intelligent, unlike the Boson NetSim

QUIX0TIC

Johnny... I will agree with you 100% and twice on Sunday when Im sitting in front of my laptop with www.XX.... oh nvm. At work or in my own lab... I would put the "full mask" or single ospf entry everytime and I know it would work. Plus, it limits me to insure that I have the correct interface instead of a group of interfaces.

But for the test... NA usually promotes the reverse mask. But at least we are on the same page.