08-14-2014 02:14 PM - edited 03-07-2019 08:23 PM
I just have a quesiton about the linkstate database. I have a point-to-point link between a couple routers(makes sense) and when I look at the database for the lsa type 1, it shows the router has 2 links in the area and one is a stub. I don't under stand how thats possible.
OSPF Router with ID (4.4.4.4) (Process ID 1)
Router Link States (Area 1)
LS age: 1136
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 4.4.4.4
Advertising Router: 4.4.4.4
LS Seq Number: 80000007
Checksum: 0xC738
Length: 60
Number of Links: 3
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 1.1.1.1
(Link Data) Router Interface address: 192.168.41.2
Number of TOS metrics: 0
TOS 0 Metrics: 10
Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.41.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 10
Can anyone explain to me what I'm seeing here? Thanks
Solved! Go to Solution.
08-14-2014 04:44 PM
Hi,
What you see is perfectly normal - it is the way OSPF describes point-to-point links in LSA1. In short, an LSA1 can carry information about four types of adjacencies: unnumbered point-to-point link to another router identified by its RID; a link to a multi-access network identified by the IP address of its DR; a stub network identified by its IP address and netmask; a virtual link identified by the RID of the other virtual link endpoint. Note that out of these four types of adjacencies, the only one that actually carries addressing information is the stub network. All other adjacency types either refer to the adjacent router's RID or the IP of the DR. A point-to-point link with addressing is represented in OSPF as a pair of adjacencies: an unnumbered point-to-point link to the other router, and a stub network representing the IP subnet on the point-to-point link.
There was a thread about this topic some time ago where I explained this OSPF behavior in more detail. You may be interested to read it - beware, though, it is somewhat large.
https://supportforums.cisco.com/discussion/11608991/ospf-termonilogy-stub-network
Best regards,
Peter
08-14-2014 02:27 PM
Full config
hostname R4
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
memory-size iomem 5
no ip icmp rate-limit unreachable
ip cef
!
!
!
!
no ip domain lookup
!
multilink bundle-name authenticated
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
archive
log config
hidekeys
!
!
!
!
ip tcp synwait-time 5
!
!
!
!
interface FastEthernet0/0
ip address 192.168.104.1 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 dallas
ip ospf 1 area 1
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 192.168.41.2 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 dallas
ip ospf 1 area 1
duplex auto
speed auto
!
router ospf 1
router-id 4.4.4.4
log-adjacency-changes
!
ip forward-protocol nd
!
!
no ip http server
no ip http secure-server
!
!
!
!
!
!
!
control-plane
!
!
!
!
!
!
!
!
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
line vty 0 4
login
!
!
end
R4#
08-14-2014 04:44 PM
Hi,
What you see is perfectly normal - it is the way OSPF describes point-to-point links in LSA1. In short, an LSA1 can carry information about four types of adjacencies: unnumbered point-to-point link to another router identified by its RID; a link to a multi-access network identified by the IP address of its DR; a stub network identified by its IP address and netmask; a virtual link identified by the RID of the other virtual link endpoint. Note that out of these four types of adjacencies, the only one that actually carries addressing information is the stub network. All other adjacency types either refer to the adjacent router's RID or the IP of the DR. A point-to-point link with addressing is represented in OSPF as a pair of adjacencies: an unnumbered point-to-point link to the other router, and a stub network representing the IP subnet on the point-to-point link.
There was a thread about this topic some time ago where I explained this OSPF behavior in more detail. You may be interested to read it - beware, though, it is somewhat large.
https://supportforums.cisco.com/discussion/11608991/ospf-termonilogy-stub-network
Best regards,
Peter
08-14-2014 05:33 PM
Thank you, that answer was outstanding.
Dallas
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: