Vikas,

> Alex,
> You say that the type 3 link will give the network
> reachability information. What if the router is used
> just for forwarding and is not attached to any
> network. Will there still be a type 3 link advertised?

No there will be no type-3 link entry for these links.
Note however, that even if a router is used purely
for forwarding, i.e., it has only unnumbered p2p interfaces,
it will still have at least one IP address and this address
most probably (but not necessarily) will be included
in the OSPF domain and announced to other routers as
a type-3 link.

> Also, in another situation when the router itself is
> the host, will there be a type 3 link to it advertised
> by the previous router?

I don't know what exactly you mean by "a host".
Anyway, if OSPF is enabled on the link, the "previous" router
will announce a type-3 without a type-1.

Alex.

> Thanks,
> -Vikas

> --- Alex Zinin <azininNEXSI.COM> wrote:

>> Feng, Vikas
>>
>> Yes, if there's a fully adjacent neighbor on a p2p
>> interface,
>> the router-LSA will have two links. One (type-1)
>> will give
>> topological information about the link (or the
>> adjacency,
>> strictly speaking), the other (type-3) will give
>> the network
>> reachability information associated with it.
>>
>> --
>> Alex Zinin
>>
>> Monday, July 02, 2001, 1:22:04 PM, Xie, Feng wrote:
>>
>> > Hi, Vikas:
>>
>> > My understanding is that two entries are added
>> for a point-to-point link
>> > if the adjancency is full. The first entry which
>> is a first type link gives
>> > the nbr rid and local IP address information. The
>> second entry which is a
>> > third type link gives the nbr ip address
>> information. In fact, for the
>> > second entry, some vendors use the network address
>> and the mask. A short
>> > comparison is given in RFC2328, p181, item 15 for
>> thest two options.
>>
>> > Feng Xie
>>
>> > -----Original Message-----
>> > From: Vikas B. Wadhwani [mailto:wvikasYAHOO.COM]
>> > Sent: Monday, July 02, 2001 3:24 PM
>> > To: OSPFDISCUSS.MICROSOFT.COM
>> > Subject: Link State Advertisments
>>
>>
>> > Hello all,
>> > This is from RFC 1583
>>
>> > Else, if the state of the interface is
>> Point-to-Point,
>> > then add links according to the following:
>>
>> > If the neighboring router is fully adjacent, add a
>> > Type 1 link (point-to-point) if this is an
>> interface
>> > to a point-to-point network, or add a Type 4 link
>> > (virtual link) if this is a virtual link. The
>> Link
>> > ID should be set to the Router ID of the
>> neighboring
>> > router. For virtual links and numbered point-to-
>> > point networks, the Link Data should specify the
>> IP
>> > interface address. For unnumbered point-to-point
>> > networks, the Link Data field should specify the
>> > interface's MIB-II [RFC 1213] ifIndex value.
>>
>> > If this is a numbered point-to-point network (i.e,
>> > not a virtual link and not an unnumbered point-to-
>> > point network) and the neighboring router's IP
>> > address is known, add a Type 3 link (stub network)
>> > whose Link ID is the neighbor's IP address, whose
>> > Link Data is the mask 0xffffffff indicating a host
>> > route, and whose cost is the interface's
>> configured
>> > output cost.
>>
>>
>> > My question is, in case of a numbered point to
>> point
>> > network, are there 2 links added for a
>> neighbouring
>> > router? If a router is connected by a PPP link to
>> > another, does the above mean that a Type 1 link
>> and a
>> > Type 3 link will be added to the router's LSA for
>> a
>> > neighbour?
>>
>> > Thanks,
>> > -Vikas
>>
>> > =====
>>
>>
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> =====

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