[Xorp-users] Questions on OSPF

Atanu Ghosh atanu at ICSI.Berkeley.EDU
Thu Sep 13 12:18:42 PDT 2007


>>>>> "kristian" == kristian  <kristian at spritelink.net> writes:

    kristian> On Thu, 13 Sep 2007 11:51:32 -0700, Atanu Ghosh
    kristian> <atanu at icsi.berkeley.edu> wrote:
    >>>>>>> "Kristian" == Kristian Larsson <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.

	       Atanu.



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