Okay, I missed that point before -- this is with an ASBR in a NSSA. In that case, there ARE no T4 LSAs. T4 LSAs are only used for a non-stubby area where the T5 LSAs have a forwarding address of 0.0.0.0. With NSSA, the interface IP is used, which is learned via T3 LSAs.
Keller Giacomarro [email protected] On Wed, Aug 15, 2012 at 5:48 AM, <[email protected]> wrote: > 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 >> _______________________________________________ >> 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 _______________________________________________ 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
