[Xorp-users] Fwd: Questions on OSPF
Hansi
hantongs at gmail.com
Mon Sep 17 17:50:19 PDT 2007
looping in the mailing list.
Thank you. One more question though.. I noticed that before RIP can be
configured, the policy parameter must be set first in order for RIP to
either advertise static and/or connected routes. Although RIP already sends
out udp packets once you configure it, it does not send out its routing
table entries not until after a policy is either imported/exported to it.
Does this also apply to OSPF?
Thanks.
Hansi.
On 9/14/07, Kristian Larsson <kristian at spritelink.net> wrote:
>
> Hansi wrote:
> > Hello Kristian, Atanu,
> >
> > Thank you answering for my queries. Let me see if I understood it
> clearly.
> >
> > For link-types: p2p or p2m, it is necessary to explicitly set the
> > neighbor parameter in order for the router running OSPF to establish
> > adjacency with another router. Broadcast link-types on the other hand
> > does not require the neighbor parameter to be explicitly set, am I
> > correct? :)
> >
> > I concur with Atanu that p2p link-types requires the neighbor statement
> > to be explicitly stated. My initial configuration does not include
> > setting the neighbor parameter, upon invoking "show ospf4 neighbor",
> > nothing comes up even though dumps from the network shows OSPF hello
> > packets have been multicast already.. The neighbor router only displays
> > [upon invoking show ospf4 neighbor] after setting the neighbor parameter
> > on both routers.
>
> Yepp, I was simply wrong. I expected XORP to work like Cisco or Juniper.
>
>
> > Regarding setting router-ID parameters to loopback 127.0.0.1
> > <http://127.0.0.1>, would it be possible for two routers running OSPF to
>
> > use the same router-ID? that is both of them are configured to 127.0.0.1
> > <http://127.0.0.1>? Since conventionally the router-ID is usually set to
>
> > the loopback, would it be possible to configure all routers in an OSPF
> > network to have the same router-ID of 127.0.0.1 <http://127.0.0.1>?
>
> No, you cannot use 127.0.0.1, at least not on both routers.
> Router-id have to be unique within your OSPF domain, one common way of
> ensuring this is to use the loopback address that you assign to a
> router. Although you are correct that 127.0.0.1 is a loopback adress,
> routes normally get one assigned from your address pool. iBGP session
> for example are normally established between loopback addresses to not
> be dependant upon a specific interface being up.
> So assign 172.16.0.1-254 (if your are using private addressing) or
> something to your loopbacks as well and you can use those.
>
> -K
>
> > On 9/14/07, * kristian at spritelink.net <mailto:kristian at spritelink.net>*
> <
> > kristian at spritelink.net <mailto:kristian at spritelink.net>> wrote:
> >
> > On Thu, 13 Sep 2007 14:58:01 -0700, Atanu Ghosh <
> > atanu at icsi.berkeley.edu <mailto:atanu at icsi.berkeley.edu>>
> > wrote:
> > >>>>>> "kristian" == kristian < kristian at spritelink.net
> > <mailto:kristian at spritelink.net>> writes:
> > >
> > > kristian> On Thu, 13 Sep 2007 12:18:42 -0700, Atanu Ghosh
> > > kristian> <atanu at icsi.berkeley.edu
> > <mailto:atanu at icsi.berkeley.edu>> wrote:
> > > >>>>>>> "kristian" == kristian < kristian at spritelink.net
> > <mailto:kristian at spritelink.net>> writes:
> > > >>
> > > kristian> On Thu, 13 Sep 2007 11:51:32 -0700, Atanu Ghosh
> > > kristian> < atanu at icsi.berkeley.edu
> > <mailto:atanu at icsi.berkeley.edu>> wrote:
> > > >> >>>>>>> "Kristian" == Kristian Larsson
> > <kristian at spritelink.net <mailto:kristian at spritelink.net>>
> > > >> >>>>>>> writes:
> > > >> >>
> > > Kristian> Hansi wrote:
> > > >> >> >> Hello All,
> > > >> >> >>
> > > >> >> >> I'm currently learning how to configure OSPFv2 on
> > two XORP
> > > >> >> >> machines just to establish adjacency with one
> > another. In a
> > > >> p2p >> >> link type, is it still necessary to explicitly
> > set the
> > > >> >> 'neighbor' >> parameter of each machine before
> > adjacency is >>
> > > >> established? >> Furthermore, would it be possible to set
> > the >>
> > > >> router-id to its >> loopback address? instead of say.. the
> > ip >>
> > > >> address of the >> interface on which ospf will be used?
> > > >> >>
> > > Kristian> The neighbor command is only useful if you are
> using a
> > > Kristian> medium on which the routers cannot broadcast and
> thus
> > > Kristian> cannot discover each other. If you're using
> ethernet
> > > Kristian> (which I presume from your NIC names) you do not
> > have to
> > > Kristian> use the neighbor statements. I would advice
> configuring
> > > Kristian> the interfaces as link-type p2p as this avoids DR
> > election
> > > Kristian> and unnecessary CPU load.
> > > >> >> I am fairly sure that it is necessary to use the
> > neighbour >>
> > > >> statements.
> > > >>
> > > kristian> Are you serious? I haven't used the XORP code in
> > quite
> > > kristian> some time now.. but at least I thought XORP
> implemented
> > > kristian> the OSPF standard. AFAIK, that includes being able
> to
> > > kristian> discover neighbors and turn up adjacencies to them.
> Is
> > > kristian> this not the case? Observe that he is running an
> > Ethernet
> > > kristian> point-to-point link, ie, it is not a non-broadcast
> > medium.
> > > kristian> Or are you saying that you can't do link-type p2p
> > without
> > > kristian> configuring neighbours ?
> > >
> > > >> If the link-type is set to "broadcast" then the
> > neighbours will
> > > >> be correctly discovered. If the link-type is set to "p2p"
> > > >> (Point-to-point) or "p2m" (Point-to-multipoint) then it is
> > > >> necessary to configure the neighbours. It has been argued
> > that it
> > > >> should not be necessary to configure the neighbours if the
>
> > > >> routers are connected via a true Point-to-point link, but
> > > >> unfortunately even in this case it is necessary to
> > configure the
> > > >> neighbour.
> > >
> > > kristian> Okey, that "kinda" makes sense. I apparently forgot
> or
> > > kristian> missed the conversation on this. What I want to
> > configure
> > > kristian> with link-type p2p is not whether or not the router
> > should
> > > kristian> try to broadcast but if it should setup one of
> those
> > > kristian> virtual router thingys, hehe. I'm not very familiar
>
> > with
> > > kristian> the terminology but (as you know) on a broadcast
> medium
> > > kristian> you first have a DR selection and all that and then
> > you're
> > > kristian> gonna run your SPF. Since SPF can't handle the
> > concept of
> > > kristian> a broadcast medium it creates a "virtual router" to
> > > kristian> represent the broadcast medium and connects all
> > routers in
> > > kristian> that broadcast domain as adjacencies to the virtual
> > > kristian> router. When I configure 'isis network
> > point-to-point' on
> > > kristian> a Cisco router I expect it to not setup one of
> these
> > > kristian> "virtual routers" in it's SPF topology. And this is
> > > kristian> different with XORP?
> > >
> > > Setting the link type to "broadcast" or "p2p" will both result in
> > the
> > > hello packets being broadcast, the distinction is that if the
> > link-type
> > > is set to "p2p" no DR election will be attempted.
> >
> > Alright, just as I expected.
> >
> > > The XORP OSPF behaves
> > > as specified in the relevant RFCs and interoperates with other
> OSPF
> > > implementations, the only difference is in configuration of a
> "p2p"
> > > where we require the neighbour to be specified, which as I
> mentioned
> > > before should not strictly be necessary.
> >
> > Okey, not what I expected. Why is it so? Just lack of time to do the
> > actual
> > implementation (although I don't see how it would actually be more
> code
> > than it is today) or has there been a policy decision against it?
> >
> > -K
> >
> >
>
>
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