injecting a default-route by an ASBR into OSPF domain and reaching the ABR

[Mehdi.a.majid1]

What I want to do here is to generate a default-route on BR4 ( Totally NSSA ) which till this part it is simple

by

BR4(config-router)#area 4 nssa default-information-originate metric-type 1

and advertisement of this default-route reaches the HQ ( ABR & ASBR ) but the HQ does not consider it,

how can I make the HQ to consider it , what are the ways to do that ?

I appreciate any help that I can get.

[Georg Pauwen]

Weird indeed. Can you attach the GNS3 file ? I am using the same IOS, so I should be able to open it...

[Mehdi.a.majid1]

Hello,

I attached the zip file

Thanks.

[Georg Pauwen]

Hello,

I opened your project, as soon as I add a static default route on BR4, it shows up in the routing table of HQ. Keep in mind that the default route needs to exist in the routing table of BR4 in order for the 'default-information originate' to work:

BR4

ip route 0.0.0.0 0.0.0.0 null 0

HQ#sh ip route

O*N2 0.0.0.0/0 [110/1] via 10.4.4.4, 00:00:02, Tunnel4

[paul driver]

Hello @Georg Pauwen

Thats whats the default route from BGP is for, hence if that is in the rib of BR4 then there should be no requirement for any static default to null to be added.

I am getting to think as this is in GNS3 that the opsf process needs to removed and re-added just for clarity as this should work.

[Georg Pauwen]

Hello,

it doesn't matter where the default route comes from, I still see the N2 route, even if it is originated by the BGP neighbor:

BR4#sh ip bgp topology *
For address family: IPv4 Unicast

BGP table version is 3, local router ID is 44.0.0.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 172.16.1.2 0 65001 i
*> 3.3.3.3/32 172.16.1.2 0 0 65001 i

HQ# sh ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - 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
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.4.4.2 to network 0.0.0.0

O*N2 0.0.0.0/0 [110/1] via 10.4.4.2, 00:00:06, Tunnel4
8.0.0.0/32 is subnetted, 1 subnets
C 8.8.8.8 is directly connected, Loopback4
9.0.0.0/32 is subnetted, 1 subnets
S 9.9.9.9 [1/0] via 44.44.44.2
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.4.4.0/24 is directly connected, Tunnel4
L 10.4.4.1/32 is directly connected, Tunnel4
44.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 44.44.44.0/29 is directly connected, GigabitEthernet0/0
L 44.44.44.1/32 is directly connected, GigabitEthernet0/0

[paul driver]

Hello

Correct Georg - hence why you dont need to add a static default route to null to the N default advertised in ospf

[Georg Pauwen]

The original problem was that either way he doesn't see the N2 route ? Is that working now ?

[paul driver]

Hello

---

@Mehdi.a.majid1 wrote:

Hello,

it does not allow when HQ knows the area 4 as totally NSSA but it allows that when HQ knows the area 4 as NSSA and BR4 has an actual default-route through BGP and is redistributed to ospf .

But I wanted to do so i.e I want to have that default-route usable in HQ advertised by BR4 to HQ which I can see that HQ can receive the advertisement of that default-route but does not consider it , since HQ considers the other redistributed routes from BGP into ospf by BR4 .

so by your understanding :

HQ(ABR & ASBR)  won't accept default-route advertised by BR4 ( area 4) and it is not possible if the area 4 is Totally NSSA ?!

---

Okay, have your tried using the "no-redistribution" to negate redistribution of the bgp prefixes but retain the default

BR4

 area 3 nssa no-redistribution default-information-originate no-summary

HQ
area 3 nssa

[paul driver]

Hello

Additionally looking at your topology you could suppress type 7 forwarding address translation so area routers off the backbone will have a forwarding address of the HQ ABR and not the ASBR

HQ
area 3 nssa translate type7 suppress-fa

[Mehdi.a.majid1]

Hello

Additionally looking at your topology you could suppress type 7 forwarding address translation so area routers off the backbone will have a forwarding address of the HQ ABR and not the ASBR

HQ
area 3 nssa translate type7 suppress-fa

you mean that by this the Routers not on the area 0 will have the forwarding address of the HQ ABR and not the ASBR ?!

but what I need here is that the when HQ which is receiving the Type-7 LSA of the default-route from BR4(ASBR) then accept it and consider it and put it in its routing table and also letting the all the routers in Area 0 and Area 1 to have that default-Route, which I tested this command that you're saying to use But it does just suppress of the Type-7 LSAs received from area 4 which is not serving my main purpose here.

Thanks.

[Mehdi.a.majid1]

Hello

and here it only negates the redistribution by no-redistribute key-word which does not cause the default-route be accepted by HQ

Thanks.

[paul driver]

Hello

i must be missing something fundermental in your setup - The only reason I mentioned it wouldn’t work in the first instance was I was in the assumption you were trying to inject a default directly from stub/NSSA  

But your default is based on a redistribution from bgp so as long as that is gettting advertised and you are also injecting it in ospf (area x nssa default- originate etc.. ) then that injection of a static from the ospf stanza should indeed work.

just to confirm in the HQ ospf stanza you have Only

Router ospf x

area x nssa

Lastly you don’t have to suppress the type 7 forwarding address it was only an additional suggestion  The default to the other areas depends on what area type they are- if they are say  t-stubs then the default will originate from the HQ abr if they are normal areas then again the default from BR4 should get propergated to them.

[paul driver]

Hello

I see only 1 n2 route from BR4 and no default - Also why do you say it should be N1 default and not a N2 I don’t see any metric manipulation from you latest config , and no redistribution from bgp unless that is have missed them.

I know you have already done this but can you attached the current config for HQ and BR4

[paul driver]

Scrach that i have the gns files you posted.