OSPF: Stub network with p2p links

karukuma · ‎03-08-2007

I have a topology A---B---C--D with OSPF running on all the routers.

B-----C is a point-2-point link.

I see that p2p link is considered as ?stub network? irrespective of router A/D running OSPF.

Logically it looks like a transit network. I see that p2p links are always stub network. Can anyone let me know the rationale behind displaying p2p as stub networks always.

===========Sample Output===========

ml1-242-12#sh ip ospf database router

OSPF Router with ID (10.10.11.10) (Process ID 1)

Router Link States (Area 0)

LS age: 1442

Options: (No TOS-capability, DC)

LS Type: Router Links

Link State ID: 10.10.11.10

Advertising Router: 10.10.11.10

LS Seq Number: 80000031

Checksum: 0xB9E1

Length: 72

Number of Links: 4

Link connected to: another Router (point-to-point)

(Link ID) Neighboring Router ID: 10.10.12.10

(Link Data) Router Interface address: 10.10.11.10

Number of TOS metrics: 0

TOS 0 Metrics: 1

Link connected to: a Stub Network

(Link ID) Network/subnet number: 10.10.11.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 1

Richard Burts · ‎03-09-2007

KARUN

I wonder if you are getting confused by the different meaning of stub network between EIGRP and OSPF. In EIGRP a stub router is a router with no dynamic neighbors behind it. But that is not what OSPF is describing when it labels a network as stub. In OSPF a stub network is a network that will not have any hosts on the network and has only routers. That is what a point to point link is, there are no hosts but only routers. That is why OSPF labels it as a stub network.

HTH

Rick

HTH

Rick

karukuma · ‎03-10-2007

Hi,

This is the definition for "Stub networks" in Jeff doyle.

"Stub networks have only a single attached router. Packets on a stub network always have either a source or a destination address belonging to that network. That is, all packets were either originated by a device on the network or are destined for a device on the network. "

My confusion is with the statement "Packets on a stub network always have either a source or a destination address belonging to that network"

As in the scenario I have mentioned the p2p link can definately behave like a Trasit n/w.

One more point I see is that if I have a n/w

A----B---C---D----|

Where the D----| is an ethernet link to a LAN segment to some hosts, OSPF states D---| as a Stub network. So "there are no hosts but only routers" is not entirely true.