[Xorp-users] Fwd: Questions on OSPF
Kristian Larsson
kristian at spritelink.net
Wed Sep 19 01:05:29 PDT 2007
Hansi wrote:
> Hello Atanu,
>
> How about static routes and connected routes? Do I still need to
> explicitly use policies in order for them to be announced? What I'm
> seeing on a network dump is only indeed the subnet for the interfaces on
> w/c OSPF is configured. I also want OSPF to announce static and
> connected routes just like what is done w/ RIP when policy static and
> connected is exported, can this be possible?
Yes, use a policy, just like with RIP.
Kristian.
> On 9/19/07, *Atanu Ghosh* <atanu at icsi.berkeley.edu
> <mailto:atanu at icsi.berkeley.edu>> wrote:
>
> Hi,
>
> OSPF will advertise the the subnets for the interfaces on which it is
> configured. In the case of OSPFv2 one subnet has to be explicitly
> configured in the config, for OSPFv3 just specifying the interface will
> advertise all associated subnets (the subnets can also be explicitly
> configured).
>
> Routes from other protocols must be explicity exported using policy.
>
> Atanu.
>
> >>>>> "Hansi" == Hansi < hantongs at gmail.com
> <mailto:hantongs at gmail.com>> writes:
>
> Hansi> looping in the mailing list. Thank you. One more question
> Hansi> though.. I noticed that before RIP can be configured, the
> Hansi> policy parameter must be set first in order for RIP to either
> Hansi> advertise static and/or connected routes. Although RIP
> Hansi> already sends out udp packets once you configure it, it does
> Hansi> not send out its routing table entries not until after a
> Hansi> policy is either imported/exported to it. Does this also
> Hansi> apply to OSPF? Thanks. Hansi.
>
> Hansi> On 9/14/07, Kristian Larsson < kristian at spritelink.net
> <mailto:kristian at spritelink.net>>
> Hansi> wrote:
>
> Hansi> Hansi wrote:
> >> Hello Kristian, Atanu,
> >>
> >> Thank you answering for my queries. Let me see if I
> understood it
> Hansi> clearly.
> >> For link-types: p2p or p2m, it is necessary to explicitly set
> >> the neighbor parameter in order for the router running OSPF to
> Hansi> establish
> >> adjacency with another router. Broadcast link-types on the other
> Hansi> hand
> >> does not require the neighbor parameter to be explicitly set, am
> Hansi> I
> >> correct? :)
> >>
> >> I concur with Atanu that p2p link-types requires the neighbor
> Hansi> statement
> >> to be explicitly stated. My initial configuration does not
> Hansi> include
> >> setting the neighbor parameter, upon invoking "show ospf4
> Hansi> neighbor",
> >> nothing comes up even though dumps from the network shows OSPF
> Hansi> hello
> >> packets have been multicast already.. The neighbor router only
> Hansi> displays
> >> [upon invoking show ospf4 neighbor] after setting the neighbor
> Hansi> parameter
> >> on both routers.
> Hansi> Yepp, I was simply wrong. I expected XORP to work like
> Hansi> Cisco or Juniper.
> >> Regarding setting router-ID parameters to loopback 127.0.0.1
> <http://127.0.0.1> <
> >> http://127.0.0.1>, would it be possible for two routers running
> Hansi> OSPF to
> >> use the same router-ID? that is both of them are configured to
> Hansi> 127.0.0.1 <http://127.0.0.1>
> >> < http://127.0.0.1>? Since conventionally the router-ID is
> Hansi> usually set to
> >> the loopback, would it be possible to configure all routers
> in an
> Hansi> OSPF
> >> network to have the same router-ID of 127.0.0.1
> <http://127.0.0.1>
> Hansi> <http://127.0.0.1>? No, you cannot use 127.0.0.1
> <http://127.0.0.1>, at
> Hansi> least not on both routers. Router-id have to be unique
> Hansi> within your OSPF domain, one common way of ensuring this is
> Hansi> to use the loopback address that you assign to a
> Hansi> router. Although you are correct that 127.0.0.1
> <http://127.0.0.1> is a loopback
> Hansi> adress, routes normally get one assigned from your address
> Hansi> pool. iBGP session for example are normally established
> Hansi> between loopback addresses to not be dependant upon a
> Hansi> specific interface being up. So assign 172.16.0.1-254 (if
> Hansi> your are using private addressing) or something to your
> Hansi> loopbacks as well and you can use those. -K
> >> On 9/14/07, * kristian at spritelink.net
> <mailto:kristian at spritelink.net> <mailto:
> Hansi> 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>>>
> 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>>>
> wrote:
> >> >>>>>> "kristian" == kristian < 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
> Hansi> 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>>>
> wrote: > >>>>>>> "kristian" == kristian
> >> <
> Hansi> 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
> Hansi> 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>>>
> wrote: > >> >>>>>>> "Kristian" ==
> >> Kristian Larsson < 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
> Hansi> OSPFv2 on
> >> two XORP > >> >> >> machines just to establish adjacency with one
> >> another. In a > >> p2p >> >> link type, is it still necessary to
> Hansi> explicitly
> >> set the > >> >> 'neighbor' >> parameter of each machine before
> >> adjacency is >> > >> established? >> Furthermore, would it be
> >> possible
> Hansi> to set
> >> the >> > >> router-id to its >> loopback address? instead of
> Hansi> say.. the
> >> ip >> > >> address of the >> interface on which ospf will be
> Hansi> used?
> >> > >> >> > Kristian> The neighbor command is only useful if you
> Hansi> are using a
> >> > Kristian> medium on which the routers cannot broadcast
> Hansi> and thus
> >> > Kristian> cannot discover each other. If you're using
> Hansi> ethernet
> >> > Kristian> (which I presume from your NIC names) you do
> Hansi> not
> >> have to > Kristian> use the neighbor statements. I would advice
> Hansi> configuring
> >> > Kristian> the interfaces as link-type p2p as this
> Hansi> avoids DR
> >> election > Kristian> and unnecessary CPU load. > >> >> I am
> >> fairly sure that it is necessary to use
> Hansi> the
> >> neighbour >> > >> statements.
> >> > >>
> >> > kristian> Are you serious? I haven't used the XORP
> Hansi> code in
> >> quite > kristian> some time now.. but at least I thought XORP
> Hansi> implemented
> >> > kristian> the OSPF standard. AFAIK, that includes
> Hansi> being able to
> >> > kristian> discover neighbors and turn up adjacencies
> Hansi> to them. Is
> >> > kristian> this not the case? Observe that he is
> Hansi> running an
> >> Ethernet > kristian> point-to-point link, ie, it is not a
> Hansi> non-broadcast
> >> medium. > kristian> Or are you saying that you can't do
> Hansi> 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
> Hansi> "p2p"
> >> > >> (Point-to-point) or "p2m" (Point-to-multipoint)
> Hansi> then it is
> >> > >> necessary to configure the neighbours. It has been
> Hansi> argued
> >> that it > >> should not be necessary to configure the neighbours
> Hansi> if the
> >> > >> routers are connected via a true Point-to-point
> Hansi> link, but
> >> > >> unfortunately even in this case it is necessary to configure
> >> the > >> neighbour.
> >> >
> >> > kristian> Okey, that "kinda" makes sense. I apparently
> Hansi> forgot or
> >> > kristian> missed the conversation on this. What I
> Hansi> want to
> >> configure > kristian> with link-type p2p is not whether or not
> >> the
> Hansi> router
> >> should > kristian> try to broadcast but if it should setup one
> Hansi> of those
> >> > kristian> virtual router thingys, hehe. I'm not very
> Hansi> familiar
> >> with > kristian> the terminology but (as you know) on a
> Hansi> broadcast medium
> >> > kristian> you first have a DR selection and all that
> Hansi> and then
> >> you're > kristian> gonna run your SPF. Since SPF can't handle
> Hansi> the
> >> concept of > kristian> a broadcast medium it creates a "virtual
> Hansi> router" to
> >> > kristian> represent the broadcast medium and connects
> Hansi> all
> >> routers in > kristian> that broadcast domain as adjacencies to
> >> the
> Hansi> virtual
> >> > kristian> router. When I configure 'isis network
> >> point-to-point' on > kristian> a Cisco router I expect it to not
> >> setup one
> Hansi> of these
> >> > kristian> "virtual routers" in it's SPF topology. And
> Hansi> this is
> >> > kristian> different with XORP?
> >> >
> >> > Setting the link type to "broadcast" or "p2p" will both
> Hansi> result in
> >> the > hello packets being broadcast, the distinction is that if
> Hansi> 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
> Hansi> other OSPF
> >> > implementations, the only difference is in configuration
> Hansi> of a "p2p"
> >> > where we require the neighbour to be specified, which as I
> Hansi> mentioned
> >> > before should not strictly be necessary.
> >>
> >> Okey, not what I expected. Why is it so? Just lack of time to
> Hansi> do the
> >> actual implementation (although I don't see how it would actually
> >> be
> Hansi> more code
> >> than it is today) or has there been a policy decision against
> Hansi> it?
> >> -K
> >>
> >>
> Hansi> _______________________________________________ Xorp-users
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>
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