Hi all,
I have some questions about Type 7 LSA default-routes propagated by ABRs.
Consider a NSSA with two ABRs. Each ABR propagate a default route with a
cost of 100 (commands are : area 1 nssa default-originate & area 1
default-cost 100).
On a Internal router directly connected to each ABR, I can see that only one
default route is in the routing table :
O*N2 0.0.0.0/0 [110/100] via 193.0.0.2, Ethernet0
But the two LSA are in the database :
IR_AS200_AREA1#sh ip ospf database nssa-external
OSPF Router with ID (192.168.108.3) (Process ID 1)
Type-7 AS External Link States (Area 1)
Routing Bit Set on this LSA
LS age: 1702
Options: (No TOS-capability, No Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 192.168.108.2
LS Seq Number: 80000001
Checksum: 0x4F63
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 100
Forward Address: 193.0.0.2
External Route Tag: 0
LS age: 318
Options: (No TOS-capability, No Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 192.168.108.4
LS Seq Number: 80000003
Checksum: 0xF37B
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 100
Forward Address: 2.0.0.1
External Route Tag: 0
My first question is, why does the IR choose one default route and not the
both ? With more investigation, I can see that it prefer the link with the
highest bandwidth. If I increase the bandwidth of the other link, the
nexthop change :
O*N2 0.0.0.0/0 [110/100] via 2.0.0.1, Serial0
if bandwidth are equal, the both routes are introduced :
O*N2 0.0.0.0/0 [110/100] via 193.0.0.2, Ethernet0
[110/100] via 2.0.0.1, Serial0
Why does it consider cost of the link ?
My other question is, on the ABR. I can see that the 0.0.0.0 LSA are in the
database. The First one is not computed because selforiginated but why the
other is not computed ? (It's a type 7 LSA , not type 3).
Thanks for help.
--
Stephane LITKOWSKI
Student in a French computer science school
EPITA Telecom & Network specialization (Paris, FRANCE)
CCNA + CCNP
EMail : [EMAIL PROTECTED]
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=52122&t=52122
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