[Xorp-users] Fwd: Questions on OSPF
Pavlin Radoslavov
pavlin at icir.org
Tue Sep 18 11:50:12 PDT 2007
Hansi <hantongs at gmail.com> wrote:
> 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? :)
Yes, XORP uses the default 127.0.0.1 loopback address for in-host
XRL IPC communications.
You could overwrite that address by setting the
XORP_FINDER_SERVER_ADDRESS environmental variable before starting
xorp_rtrmgr. Note that you need to set it before starting any other
XORP-related program including xorpsh otherwise it won't know know
how to connect to the XORP finder.
Why do you want to change the loopback address?
If it is for the purpose of assigning unique loopback address for
configuring OSPF, then you could try to add that unique address as
an alias IP address to the loopback interface.
On the other hand, I could be wrong, but assigning the unique
protocols/ospf4/router-id doesn't require that the value really is
an IP address that is assigned to an interface. For management
purpose you might want to do that, but strictly speaking it is
sufficient to be unique within the OSPF domain.
Pavlin
> 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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