[Xorp-users] Fwd: Questions on OSPF
Kristian Larsson
kristian at spritelink.net
Tue Sep 18 05:05:38 PDT 2007
Hansi wrote:
> Thanks Kristian. It appears that a loopback interface alias is created
> in order to use the loopback interface as the router ID. One more
> question though.. does OSPF use policies to announce routes? Is it
> necessary to import/export policy in ospf similar to what was done with
> RIP before RIP starts announcing its routes?
Oh, I don't remember the behaviour of XORP, you'll have to try for
yourself, or if anyone else can answer ;)
I haven't worked with OSPF in some time now but I believe most
implementations only advertise LSAs for those interfaces where you
actually talk OSPF and that you have to redistribute connected and
static routes. Somewhere in the back of my head I have a memory of
Juniper redisting direct routes by default but I'm probably wrong.
Just try it out ;)
-K
> Hansi.
>
> On 9/18/07, *Kristian Larsson* <kristian at spritelink.net
> <mailto:kristian at spritelink.net>> wrote:
>
> Hansi wrote:
> > including the mailing list
>
> Sorry for not replying earlier.
>
> > hmm... seems like after changing my loopback address from
> 127.0.0.1 <http://127.0.0.1>
> > < http://127.0.0.1> to any private address such as 172.16.0.1
> <http://172.16.0.1>
> > <http://172.16.0.1>, this error was encountered:
>
> Yes, XORP uses the loopback interface for IPC communication, it
> therefore by default, binds to 127.0.0.1 <http://127.0.0.1>. You
> should not replace
> 127.0.0.1 <http://127.0.0.1> with 172.16.0.1 <http://172.16.0.1> but
> rather just add 172.16.0.1 <http://172.16.0.1>
> Can be accomplished with
>
> ip address add 172.16.0.1/32 <http://172.16.0.1/32> dev lo
>
> on a Linux machine.
>
> Kristian.
>
>
> >
> > [ 2007/09/17 16:53:31 ERROR xorp_rtrmgr:6201 LIBCOMM +359
> comm_sock.c
> > comm_sock_bind4 ] Error binding socket (family = 2, my_addr =
> 127.0.0.1 <http://127.0.0.1>
> > <http://127.0.0.1>, my_port = 19999): Cannot assign requested
> address
> > [ 2007/09/17 16:53:31 ERROR xorp_rtrmgr:6201 RTRMGR +243
> main_rtrmgr.cc
> > run ] Cannot assign requested address: a finder may already be
> running.
> >
> > seems like the rtrmgr binds to 127.0.0.1 <http://127.0.0.1>
> <http://127.0.0.1> only. is
> > there any way to change this? just in case i want my router-id to
> bind
> > to a loopback interface with a private assigned IP instead of
> 127.0.0.1 <http://127.0.0.1>
> > <http://127.0.0.1>? :)
> >
> >
> > On 9/17/07, * Hansi* <hantongs at gmail.com
> <mailto:hantongs at gmail.com> <mailto: hantongs at gmail.com
> <mailto:hantongs at gmail.com>>> wrote:
> >
> > Thank you Kristian. 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
> <mailto:kristian at spritelink.net>
> > <mailto:kristian at spritelink.net
> <mailto: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>
> > <http://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> <http://127.0.0.1
> <http://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>
> > <http://127.0.0.1> < http://127.0.0.1>?
> >
> > No, you cannot use 127.0.0.1 <http://127.0.0.1>
> <http://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
> <http://127.0.0.1>
> > < http://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>
> > <mailto:kristian at spritelink.net
> <mailto:kristian at spritelink.net>> <mailto:
> > kristian at spritelink.net <mailto:kristian at spritelink.net>
> <mailto:kristian at spritelink.net <mailto:kristian at spritelink.net>>>* <
> > > kristian at spritelink.net
> <mailto:kristian at spritelink.net> <mailto:kristian at spritelink.net
> <mailto:kristian at spritelink.net>>
> > <mailto: kristian at spritelink.net
> <mailto:kristian at spritelink.net>
> > <mailto: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> <mailto:atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>>
> > <mailto: atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu> <mailto:atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>>>>
> > > wrote:
> > > >>>>>> "kristian" == kristian <
> kristian at spritelink.net <mailto:kristian at spritelink.net>
> > <mailto:kristian at spritelink.net
> <mailto:kristian at spritelink.net>>
> > > <mailto: kristian at spritelink.net
> <mailto:kristian at spritelink.net>
> > <mailto: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>
> > <mailto:atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>>
> > > <mailto: atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>
> > <mailto:atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>>>> wrote:
> > > > >>>>>>> "kristian" == kristian <
> > kristian at spritelink.net <mailto:kristian at spritelink.net>
> <mailto: kristian at spritelink.net <mailto:kristian at spritelink.net>>
> > > <mailto: kristian at spritelink.net
> <mailto:kristian at spritelink.net>
> > <mailto: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>
> > <mailto:atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>>
> > > <mailto: atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>
> > <mailto:atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>>>> wrote:
> > > > >> >>>>>>> "Kristian" == Kristian Larsson
> > > <kristian at spritelink.net
> <mailto:kristian at spritelink.net> <mailto:kristian at spritelink.net
> <mailto:kristian at spritelink.net>>
> > <mailto: kristian at spritelink.net
> <mailto:kristian at spritelink.net> <mailto: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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