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#31 Routraxx

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Posted 04 August 2009 - 04:29 PM

You forgot:

7) K-values



Hi Jamalus,

K-values matching is a mandatory condition in EIGRP and not in OSPF.
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#32 Migael

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Posted 05 August 2009 - 12:13 AM

If I don't want an interface advertising it's IPs, how do I do that? Here's an excerpt from my lab, I don't want anyone on 10.x.x.x to get to 172.x.x.x.

Gateway#sho run inter fa0/2
interface FastEthernet0/2
description Management
ip address 172.18.3.1 255.255.252.0

Gateway#sho run | begin router ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
redistribute static subnets
passive-interface GigabitEthernet1/0
network 10.1.0.0 0.0.255.255 area 0
network 10.2.0.0 0.0.255.255 area 0
network 10.3.0.0 0.0.255.255 area 0
default-information originate always

Gateway#sho ip route 172.18.0.0
Routing entry for 172.18.0.0/16, 2 known subnets
Attached (2 connections)
Variably subnetted with 2 masks
Redistributing via ospf 1
C 172.18.0.0/22 is directly connected, FastEthernet0/2
L 172.18.3.1/32 is directly connected, FastEthernet0/2


Thanks!
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#33 laf_c

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Posted 16 August 2009 - 01:53 AM

Hy,

Here are two routers directly connected and one router has a loopback interface defined:
interface Lo 20
ip address 172.16.20.1 255.255.255.0


Then for the OSPF process
router ospf 1
network 172.16.20.0 0.0.0.255 area 0


Why the neighbor router(which also runs OSPF) see the route
O 172.16.20.1/32 [110/1] .... with /32 prefix instead of /24 ?

Thanks !
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#34 laf_c

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Posted 17 August 2009 - 10:48 PM

Meanwhile I did some search and here the answer:
Loopbacks are considered host routes in OSPF, and they're advertised as /32. It is all wrote down at section 9.1 of RFC 2328.

Now I have another question on OSPF:
I have an ASBR and I want to redistribute some static routes to other areas this way:
32.0.0.0 I want to redistribute it as an E2 route
the rest of static routes I want to be redistributed as E1 routes.

I tried with a route-map doing this, but no luck until now:

route-map STATIC_32 permit 10
match ip address 25
set metric-type type-2

and then on the OSPF process here's what I get

ASBR(config-router)#redistribute route-map STATIC_32
Unknown routing protocol - "redistribute route-map STATIC_32"
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#35 Son_Kazama

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Posted 27 August 2009 - 09:27 PM

Thanks, DF, for such a wonderful post!
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#36 DarkFiber

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Posted 30 August 2009 - 06:22 AM

Hy,

Here are two routers directly connected and one router has a loopback interface defined:
interface Lo 20
ip address 172.16.20.1 255.255.255.0


Then for the OSPF process
router ospf 1
network 172.16.20.0 0.0.0.255 area 0


Why the neighbor router(which also runs OSPF) see the route
O 172.16.20.1/32 [110/1] .... with /32 prefix instead of /24 ?

Thanks !


interface Lo 20
ip address 172.16.20.1 255.255.255.0
ip ospf network point-to-point
end
wr mem

this will give you the result that u need, by default ospf set all loopabcks to /32 when sending its updates.
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#37 DarkFiber

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Posted 30 August 2009 - 06:23 AM

Meanwhile I did some search and here the answer:
Loopbacks are considered host routes in OSPF, and they're advertised as /32. It is all wrote down at section 9.1 of RFC 2328.

Now I have another question on OSPF:
I have an ASBR and I want to redistribute some static routes to other areas this way:
32.0.0.0 I want to redistribute it as an E2 route
the rest of static routes I want to be redistributed as E1 routes.

I tried with a route-map doing this, but no luck until now:

route-map STATIC_32 permit 10
match ip address 25
set metric-type type-2

and then on the OSPF process here's what I get

ASBR(config-router)#redistribute route-map STATIC_32
Unknown routing protocol - "redistribute route-map STATIC_32"




ASBR(config-router)#redistribute static subnets route-map STATIC_32
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#38 laf_c

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Posted 24 September 2009 - 10:29 PM

Hi Friends,

Good to know that ppl are diving into concepts rather than braindumping them....awesome...Now for the OSPF neighbor relationships...

Following are the parameters i feel, must match for a neighbor relationship to form in OSPF:-

5) Subnet mask

And remember there's a logical AND between above parameters..... ;)



Subnet mask ! Does this means each neighbor has to have the same mask value in order to establish adjacencies? I mean I had a router with 100.0.0.1/16 and 100.0.0.2/24 and couldn't figure it why doesn't work!!
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#39 Brian McGahan

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Posted 25 September 2009 - 01:35 AM

Subnet mask ! Does this means each neighbor has to have the same mask value in order to establish adjacencies? I mean I had a router with 100.0.0.1/16 and 100.0.0.2/24 and couldn't figure it why doesn't work!!


Normally yes. The exceptions would be with unnumbered or PPP encapsulated links. Per RFC 2328, OSPF Version 2:


9.5. Sending Hello packets

Hello packets are sent out each functioning router interface.
They are used to discover and maintain neighbor
relationships.[6] On broadcast and NBMA networks, Hello Packets
are also used to elect the Designated Router and Backup
Designated Router.

The format of an Hello packet is detailed in Section A.3.2. The
Hello Packet contains the router's Router Priority (used in
choosing the Designated Router), and the interval between Hello
Packets sent out the interface (HelloInterval). The Hello
Packet also indicates how often a neighbor must be heard from to
remain active (RouterDeadInterval). Both HelloInterval and
RouterDeadInterval must be the same for all routers attached to
a common network. The Hello packet also contains the IP address
mask of the attached network (Network Mask). On unnumbered
point-to-point networks and on virtual links this field should
be set to 0.0.0.0.


HTH,
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#40 DarkFiber

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Posted 08 October 2009 - 07:13 PM

Any more questions guys :)

Hi Brian, Glad your here
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#41 koolpep

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Posted 08 October 2009 - 08:14 PM

[quote name='DarkFiber' date='30 April 2009 - 08:20 AM' timestamp='1241043655' post='833888']
Hello Guys , any questions regarding this Topic : )Hello Sir Can I get lab for the OSPF
[/quot
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#42 DarkFiber

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Posted 09 October 2009 - 08:08 PM

[quote name='koolpep' date='08 October 2009 - 12:14 PM' timestamp='1254996870' post='860980']
[quote name='DarkFiber' date='30 April 2009 - 08:20 AM' timestamp='1241043655' post='833888']
Hello Guys , any questions regarding this Topic : )Hello Sir Can I get lab for the OSPF
[/quot
[/quote]

Hmmm, man check cisco press book & sybext, they got full OSPF labs, just lab them on dynamips and start config.
tot be honest im not good @ dynamips
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#43 heera4all

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Posted 22 October 2009 - 03:48 AM

hello,
my question is how many routes an ospf lsu packet can contain.
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#44 DarkFiber

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Posted 25 October 2009 - 11:22 PM

hello,
my question is how many routes an ospf lsu packet can contain.


You mean how many LSA will be in the OSPF packet type LSU, i think it depends on the MTU of the interface, i didn't find a specific document for a number, when i quicked searched on it, Its not like RIP which got 24 routes in case of MD5 is being used.

Also it depends, if its a new update, it will only contain 1 LSA for this update, if its a new neighbor it will contain as much LSAs as possible.
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#45 MaliKue

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Posted 26 October 2009 - 07:06 PM

what is the defference between type3 LSA and type 4 LSA
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#46 laf_c

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Posted 26 October 2009 - 07:10 PM

what is the defference between type3 LSA and type 4 LSA


LSA 3 – Summary net link entry – originated by ABRs. It describes links between ABR and Internal routers of the local area. These entries are flooded throughout the backbone area to other ABRs. LSA 1 are sent as LSA 3 into other areas by the ABRs.
When a link in one area changes, the adjacent routers originate in LSA 1 and flood them within the area, causing intra-area routers to re-run the SPF and update the routing table. But ABRs do not announce topological information between areas. ABRs only inject routing information into other areas, which is basically a distance-vector technique.
OSPF specification states that ABRs are restricted to considering LSA 3 only from the backbone are to avoid routing loops.
show ip ospf database  should see networks in other areas and the ABR that advertise them.
Routes learned via LSA 3 are denoted by an IA (Inter-Area Routes) in the routing table.

LSA 4 – ASBR summary link entry – originated by ABRs. It describes reach ability to ASBRs. Flooded throughout the backbone area to the other ABRs. Advertises the ASBR (Router ID) and not a network.
Same as LSA 3, except the network mask field is always 0.
Not flooded to Stub or Totally Stubby networks.
Routers in non-area 0, should see Router ID of ASBR and its ABR to get there
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#47 laf_c

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Posted 12 November 2009 - 08:26 PM

Hi guys,

Me again with a funny OSPF scenario.

R1 R2 R3 R4 all connected through a a central switch. I attached the whole scenario. Here's a resumee:

R1: L0 - 141.85.37.1, E0 - 199.1.1.4
R2: E0 - 199.1.1.5, E1 - 199.2.1.1
R3: L0 - 172.17.1.1, E0 - 199.1.1.6
R4: E0 - 199.1.1.7

Which router will be elected as DR and which one will be elected as BDR?
At first glance I would say R3 as DR and R1 as BDR. The result in lab was ?@$!; OSPF choose R2 as DR and R4 as BDR.

What are your thoughts?

Attached Files


Edited by laf_c, 12 November 2009 - 08:29 PM.

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#48 Haidar

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Posted 14 November 2009 - 01:57 AM

Hi guys,

Me again with a funny OSPF scenario.

R1 R2 R3 R4 all connected through a a central switch. I attached the whole scenario. Here's a resumee:

R1: L0 - 141.85.37.1, E0 - 199.1.1.4
R2: E0 - 199.1.1.5, E1 - 199.2.1.1
R3: L0 - 172.17.1.1, E0 - 199.1.1.6
R4: E0 - 199.1.1.7

Which router will be elected as DR and which one will be elected as BDR?
At first glance I would say R3 as DR and R1 as BDR. The result in lab was ?@$!; OSPF choose R2 as DR and R4 as BDR.

What are your thoughts?


Strange!

I would've thought that it's R4 as DR.

Priorities all defaulted? what about the sequence when they were powered up?

I couldn't open the zipped document.
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#49 DarkFiber

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Posted 14 November 2009 - 05:41 AM

Strange!

I would've thought that it's R4 as DR.

Priorities all defaulted? what about the sequence when they were powered up?

I couldn't open the zipped document.


1- priority
2- if priorities are equal choose the highest RID between all routers.

RID = highest logical IP, if no logical interfaces it will be highest physical IP.

R1: L0 - 141.85.37.1, E0 - 199.1.1.4, R1 RID = 141.85.37.1
R2: E0 - 199.1.1.5, E1 - 199.2.1.1 R2 RID = 199.2.1.1
R3: L0 - 172.17.1.1, E0 - 199.1.1.6 R3 RID = 172.17.1.1
R4: E0 - 199.1.1.7 R4 RID = 199.1.1.7

its clear that DR will be R2 & BDR will be R4

Its just tricky

Edited by DarkFiber, 14 November 2009 - 05:42 AM.

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#50 khamel

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Posted 03 January 2010 - 09:02 PM

Thanks for the summary! Had one of my own but it lacked specific technical details which you added and overwhelmed even. Switched to using your.
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#51 DarkFiber

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Posted 04 January 2010 - 03:55 AM

Thanks for the summary! Had one of my own but it lacked specific technical details which you added and overwhelmed even. Switched to using your.



Thanks :)
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#52 king kong

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Posted 02 September 2010 - 01:05 PM

thanks dude.
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#53 Ahmed Ashfaque

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Posted 04 October 2010 - 05:40 PM

Hello Every One,
Any have good idea about sham-link, I tried so many articles, they are with configurations with no explanation like what Sham-link is basically for?

kindly refer any good article or your comments. Regards,
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#54 vgbest

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Posted 15 June 2011 - 08:58 PM

GREAT POST ..

though I'm reading to understand. :)
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#55 Mayur_Maxx

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Posted 17 June 2011 - 07:28 PM

Thanks Friends

This will be very useful for Us
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#56 Ken_masters

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Posted 09 July 2011 - 06:44 AM

Hello,

I read that on NBMA networks OSPF packets use unicast transmissions, so we need to put manual neighbors.
So I don't understand why we must use the "broadcast" word on frame-relay command if packets use unicast ??
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#57 teekash

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Posted 21 October 2012 - 08:44 PM

Hi All this is my first post everPosted Image , i would like to know, what is the advantage of adding networks with a wildcard mask instead of using classful network addresses??
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#58 rahul.sawant85

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Posted 13 February 2013 - 02:55 PM

hello darkfiber i am new in cisco and i dont have hands on experience on so pls guide me .i am ccna certified


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