[Xorp-users] Fwd: Questions on OSPF
Hansi
hantongs at gmail.com
Mon Sep 17 17:50:43 PDT 2007
including the mailing list
hmm... seems like after changing my loopback address from 127.0.0.1 to any
private address such as 172.16.0.1, this error was encountered:
[ 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,
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 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? :)
On 9/17/07, Hansi <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> 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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