AI, ML, Development + Cisco Learning Blog Learning about Machine Learning, Artificial Intelligence, related devlopment topics and formerly Routing and Switching, Datacenter, Security and other topics, CCIE #23664, Frank Wagner

23. Februar 2009

OSPF authentication types

Filed under: IGP Routing,OSPF — ocsic @ 13:50

Just for rememberance, but might be important to know the type of authentication in the lab. OSPF know three different kind of authentications. Well to be honest, there are more, but only the first three are defined:

Type Authentication RFC

0        No Authentication                          [RFC1583]
1        Simple Password Authentication             [RFC1583]
2        Cryptographic authentication               [RFC2328]
3-65535  Unassigned

Important, OSPF know key rollover only for encrypted keys. If you have several neighbors with different key, rollover works on one interface, but only for encrypted keys. Wit EIGRP this is not possible. You will need a new interface for more than one neighbor with a different key.

Example for two neighbors with different encrypted keys each (sync can last up to 20 minutes, you have to be patient!):
int s1/0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 CISCO1
ip ospf message-digest-key 2 md5 CISCO2

To configure type „0“ authentication use:


ip ospf authentiation null


19. September 2008

ospf network definition for adding all interfaces / default route

Filed under: IGP Routing,OSPF — ocsic @ 14:30

What’s the difference?

router ospf 1

network area 0


router ospf 1

network area 0

Both add all existing interfaces into area 0 and all later added interfaces also. Both statements are valid.

For the default route it seems the same:

ip route f1/1


ip route f1/1

both work, sending traffic to the default gatewayf f1/1.

What IOS does not permit is a mixture for example.:


SW1(config)#ip route f1/1
%Inconsistent address and mask

Both statements are the same. Since both have the same logical „AND“ing result for the host part, namely „0“.

0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1


0 0 0 0 0 0 0 0


0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0


0 0 0 0 0 0 0 0

14. November 2006

LSA types in different areas

Filed under: OSPF — ocsic @ 14:08
  • Backbone Area: 1,2,3,4,5
  • Non-Backbone Area, non-stub: 1,2,3,5,
  • Stub: 1,2,3,4
  • Totally stubby: 1,2 (except also for type-3 default route)
  • Not-so-stubby: 1,2,3,4,7
  • stub: area number stub, 1,2,3,4
  • totally stubby: area number stub no-summary,1,2 def 3
  • no-so-stubby: area number nssa,1,2,3,4,7
  • not-so-totally-stubby: area 1 nssa no-summary ,1,2,def 3, 7

Source: TCP/IP Vol1, page 484

20. Juli 2006

OSPF packet header

Filed under: OSPF — ocsic @ 09:26

OSPF Packet header

Basic OSPF details

Filed under: OSPF — ocsic @ 09:10

For startup OSPF needs a process ID. This could be confusing. This is not at all an autonomous system number or anything else. It’s just the ID of the OSPF process running in the memory of the router.

router ospf [process id]

for example:

router ospf 1

Cisco allows more than one ospf process on the router. So you can define more than one OSPF process.

Most of the OSPF commands are configured under the „router“ command. Some are configured on the „interface“ itself. For example interface cost.

The basic network definition has three parameters:

network ip add wildcard-mask area area-number

19. Juli 2006

OSPF process clearing

Filed under: OSPF,Tips / Hints — ocsic @ 12:45

A very helpful command to reset the current ospf process is:

clear ip ospf process

This restarts the process and let OSPF re-establish adjacencies.

What i found out, ist that the router-id does not change, when you have set up another ip address for a loopback.

But then resetting the OSPF process with the „router-id“ command is successful.

So for example the current router-id is because of loopback0 with ip add and  you change the ip address of loopback0, the OSPF process does not update the router-id, even with „clear ip ospf proc“ not.

„router-id“ does reset the OSPF process too. So setting it and then removing with „no router-id“ would do the trick. Anyway, you can of course set the right id before. Just to mention that. Hope i made that clear. 🙂

OSPF area defintion with interfaces

Filed under: OSPF — ocsic @ 11:31

I have see this on some LAB examples. It looks like this:

interface serial0

ip add

router ospf 1

And then there are two possible solutions for the wildcard mask within the network definition.

1. network area 0

and i have also seen this:

2. network area 0
So both area definitions are possbile. Not that with the secound example, it’s not necessary to calculate a wildcard mask for OSPF.But for some reason i don’t feel like using it. But on the other side, this make sure you don’t misconfigure the OSPF network wildcard mask.

17. Juli 2006

ospf and area range

Filed under: OSPF — ocsic @ 16:22

If you don’t want to show up all interface from one area, you can summarize them with the „area area-id range ip-address mask [advertise | not-advertise] [cost cost]“ command.

For example to summarize the subnet for area 3:

area 3 range

So area 3 would just show up as one subnet to other ospf areas.


ospf and virtual-link

Filed under: OSPF — ocsic @ 16:07

Each area has to be connected to area 0. If this is not the case, there is the possibility to set up an virtual link.

OSPF Virtual Link

Then you could transit one area with „virtual-link“. This is done on router with ID under „router ospf“ like that:

area 1 virtual-link

And on router with area 3 like this:

area 1 virtual-link

Make sure that you use the router ID and not an IP address. Lookup the ID with „show ip protocols“.


23. Mai 2006

OSPF Route Types

Filed under: OSPF — ocsic @ 17:54

In the routing table you can see descriptions about the entries.

Here are some more explanations.

  • O – OSPF
  • IO – OSPF inter area
  • N1 – OSPF NSSA external type 1
  • N2 – OSPF NSSA external type 2
  • E1 – OSPF external type 1
  • E2 – OSPF external type 2
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