I set the RID of the ASBR to 127.0.0.1, but it didn't change the Type-5
LSA (I didn't mention that the route in question was redistributed into
an NSSA area)
So I changed set it back, and changed RID of the ABR that is doing the
7-to-5 conversion to 127.0.0.1.
Here is the resulting Type5 LSA:
Berta#sh ip ospf database external 1.1.1.0
OSPF Router with ID (192.168.24.4) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 8
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 1.1.1.0 (External Network Number )
Advertising Router: 127.0.0.1
LS Seq Number: 80000001
Checksum: 0x465D
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 192.168.13.3
External Route Tag: 0
The "Advertising Router" changed, but the "Forward Address" is still the
same, and reach-ability for this address is provided by the Type3 LSA.
So there still doesn't seem to be a need for a Type4.
However, on the 7-to-5 translator, I added "area 1 nssa translate type7
suppress-fa" to the OSPF config. Now the external LSA looks like this:
Berta#sh ip ospf database external 1.1.1.0
OSPF Router with ID (192.168.24.4) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 10
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 1.1.1.0 (External Network Number )
Advertising Router: 127.0.0.1
LS Seq Number: 80000002
Checksum: 0x40DB
Length: 36
Network Mask: /24
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 20
Forward Address: 0.0.0.0
External Route Tag: 0
So now I see the need for type 4 LSA - when the forward address is
0.0.0.0.
Other than when suppress-fa is enabled, when would the forward address
ne set to 0?
Doug
-------- Original Message --------
Subject: Re: [OSL | CCIE_RS] OSPF LSA Type 3 and Type 4 Confusion ?
From: Keller Giacomarro <[email protected]>
Date: Tue, August 14, 2012 11:02 pm
To: [email protected]
Cc: MANISH <[email protected]>, [email protected]
Set the router ID of the ASBR to 127.0.0.1. The router ID of the ASBR
does not have to be routable. Or is there something else in your
question I'm not understanding?
Keller Giacomarro
[email protected]
On Tue, Aug 14, 2012 at 8:26 PM, <[email protected]> wrote:
> After some thought, I labbed this up and now have the same doubts
> again... Here's a type 5 LSA:
>
> Berta#sh ip ospf database external 1.1.1.0
>
> OSPF Router with ID (192.168.24.4) (Process ID 1)
>
> Type-5 AS External Link States
>
> Routing Bit Set on this LSA
> LS age: 20
> Options: (No TOS-capability, DC)
> LS Type: AS External Link
> Link State ID: 1.1.1.0 (External Network Number )
> Advertising Router: 192.168.13.1
> LS Seq Number: 80000001
> Checksum: 0x5A52
> Length: 36
> Network Mask: /24
> Metric Type: 2 (Larger than any link state path)
> TOS: 0
> Metric: 20
>>>>>>>>>Forward Address: 192.168.13.3 <<<<<<<<<<<<<<<<<<<<<<<<<<
> External Route Tag: 0
>
> Notice the forward address above, 192.168.13.3. On the same router:
>
> Berta#sh ip ospf database summary 192.168.13.0
>
> OSPF Router with ID (192.168.24.4) (Process ID 1)
>
> Summary Net Link States (Area 2)
>
> Routing Bit Set on this LSA
> LS age: 1660
> Options: (No TOS-capability, DC, Upward)
> LS Type: Summary Links(Network)
> Link State ID: 192.168.13.0 (summary Network Number)
> Advertising Router: 192.168.24.2
> LS Seq Number: 80000001
> Checksum: 0x9BA5
> Length: 28
> Network Mask: /24
> TOS: 0 Metric: 2
>
> So this Type 3 LSA has all the reach-ability information needed to
> forward this packet to the ASBR without a Type4 LSA. Speaking of the
> Type 4 LSA, here it is:
>
> Berta#sh ip ospf database asbr-summary
>
> OSPF Router with ID (192.168.24.4) (Process ID 1)
>
> Summary ASB Link States (Area 2)
>
> Routing Bit Set on this LSA
> LS age: 1902
> Options: (No TOS-capability, DC, Upward)
> LS Type: Summary Links(AS Boundary Router)
> Link State ID: 192.168.13.1 (AS Boundary Router address)
> Advertising Router: 192.168.24.2
> LS Seq Number: 80000001
> Checksum: 0x79C6
> Length: 28
> Network Mask: /0
> TOS: 0 Metric: 1
>
> This type 4 LSA doesn't have any information that we don't already have
> with the type 3. So now I'm back to where Manish began... When/why do we
> need the type 4?
>
> Thanks!
>
> Doug
>
>
> -------- Original Message --------
> Subject: [OSL | CCIE_RS] OSPF LSA Type 3 and Type 4 Confusion ?
> From: MANISH <[email protected]>
> Date: Tue, August 14, 2012 9:40 am
> To: [email protected]
>
> Hi All,
>
> can some one please explain me the difference in LSA Type 3 and LSA Type
> 4
>
> as per my understanding
>
> LSA Type 3 is used for inter area routes ........meaning all the Type
> 1/2
> inside an area when crosses in to other area will be advertised using
> type
> 3
>
> LSA Type 4 is the IP address of ASBR.
>
> my confusion is if we already know about ip add of ASBR through Type 3
> since every thing gets flooded in to other areas why do we need type 4
> explicitly to define ip add of ASBR.
>
>
> I read many blogs and other sources but still could not undersdtand.
>
> take a look at this blog explanation, will fa0/0 of R6 not be known to
> other areas using type 3 lsa ?
>
> http://blog.ipexpert.com/2009/11/04/ospf-type-4-lsa-the-forward-address-part-1/
>
>
>
> Thank You.
> Manish
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> _______________________________________________
> For more information regarding industry leading CCIE Lab training, please
> visit www.ipexpert.com
>
> Are you a CCNP or CCIE and looking for a job? Check out
> www.PlatinumPlacement.com
>
> http://onlinestudylist.com/mailman/listinfo/ccie_rs
_______________________________________________
For more information regarding industry leading CCIE Lab training, please visit
www.ipexpert.com
Are you a CCNP or CCIE and looking for a job? Check out
www.PlatinumPlacement.com
http://onlinestudylist.com/mailman/listinfo/ccie_rs
