[dev] Need Information About SR Tunnel Creation Using OSPF in FRR

[Shuvro]

Hi Oliver,

Thanks a lot for your candid reply.It helped me immensely.One more point I
wish to clarify regarding SR config:

When I configure OSPF-SR ,I can see that the connected interfaces are
getting adj SID labels though it has not been configured explicitly.

You can see the below snippet:
config Snippet:
-----------------
router ospf
 ospf router-id 1.1.1.1
 network 1.1.1.1/32 area 0
 network 20.1.1.0/24 area 0
 capability opaque
 mpls-te on
 mpls-te router-address 1.1.1.1
 segment-routing on
 segment-routing global-block 10000 19999
 segment-routing node-msd 8
 segment-routing prefix 1.1.1.1/32 index 1100
 router-info area

Show CLI Snippet:
-------------------------------
sh ip ospf database segment-routing

OSPF Segment Routing database for ID 1.1.1.1

SR-Node: 2.2.2.2 SRGB (Size/Label): 10000/10000 Algorithm(s): SPF MSD: 8

    Prefix or Link  Label In  Label Out       Node or Adj. SID  Interface
        Nexthop
------------------  --------  ---------  ---------------------  ---------
---------------
        2.2.2.2/32     11200      11200      SR Pfx (idx 1200)       eth3
       20.1.1.2

SR-Node: 1.1.1.1 SRGB (Size/Label): 10000/10000 Algorithm(s): SPF MSD: 8

    Prefix or Link  Label In  Label Out       Node or Adj. SID  Interface
        Nexthop
------------------  --------  ---------  ---------------------  ---------
---------------
        1.1.1.1/32         0          0      SR Pfx (idx 1100)         lo
        1.1.1.1
       20.1.1.1/32     50001        pop    SR Adj. (lbl 50001)       eth3
       20.1.1.2
       20.1.1.1/32     50000        pop    SR Adj. (lbl 50000)       eth3
       20.1.1.2

Here,20.1.1.2 is the connected interface which has appeared twice with two
adj labels being mapped to it.Any pointer why is it so?

Why adj-SID is getting configured without explicit configuration and why
same interface is getting two labels?


Thanks,
Shuvro

On Tue, Apr 9, 2019 at 5:09 PM <olivier.dugeon at orange.com> wrote:

> Hi Shuvro,
>
> Le 09/04/2019 à 08:51, Shuvro a écrit :
>
> Hi Team,
>
> I want to create one SR tunnel between 4 FRR nodes where one node will be
> used as head-end node which will be used to push the label stack.SRGB in
> all these nodes will be same(10000-19999).I am going to use the loopback
> interface for node SID. I have few questions in this regard:
> (1) How can I use one dummy interface as loopback in case of SR,I have
> tried using a dummy interface previously for vanilla OSPF and BGP,it works
> fine but in case of SR config,it complains:
> not a loopback interface
>
> For that purpose, just add `ip address 10.0.0.1` (change 10.0.0.1 by the
> IP address is suitable for your testbed) for the lo interface in the
> zebra.conf file. This will add IP address to the loopback interface. You
> could also do that at the Linux layer with the `ip addr add ...` command.
> But, I think it is safer to configure it within FRR
>
> (2)To provision the tunnel effectively,how can I use prefix SID for the
> connected interfaces.
> I was using:
> ip route x.x.x.x/mask <gateway> label as the node SID
> Here,how can I configure prefix SID for the prefixes other than the node
> prefix.
>
> UP to now, prefix SID are not supported. What you could perform is to add
> a static route to a given prefix and specify the label stack. Be careful
> for the label value. It is the real label value not the node SID. In your
> case, if the first router has a node SID equal to 100, the label will 10100
> regarding your SRGB.
>
> (3)How can I verify the tunnel in the data plane (e.g. ping works fine).
>
> Of course ping will work without SR due to OSPF routing. If you would
> check that the configuration is in place, you could perform a 'show ip
> route', 'show mpls table', show mpls fec' and at the Linux kernel 'ip
> route'. Now, if you run ping command, just launch a
> whiresharl/tshark/tcpdump tool to check that the ICMP packets are correctly
> encapsulated with MPLS.
>
>
> Any sample config in this regard will be helpful.
>
>
> OSPF Segment Routing documentation is here:
> http://docs.frrouting.org/projects/dev-guide/en/latest/ospf-sr.html#ospf-segment-routing
> and you could find some examples in OSPF SR topotest here:
> http://docs.frrouting.org/projects/dev-guide/en/latest/ospf-sr.html#ospf-segment-routing
> (the configurations are under r1 - r4 directory)
>
> Let me know if you have any trouble
>
> Regards
>
> Olivier
>
>
> Thanks,
> Shuvro
>
>
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