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Linux Networking Systems Administration

Notes from debugging OSPF between cisco devices and Linux FRR ospfd configs

When trying to find why my ospf configs were not sending the correct costing from Linux -> Cisco devices, I found some useful commands that I thought I would note down for future reference.

Linux – Using vtysh

My ospfd.conf looks something like this:

[root@dhcptst1 ~]# cat /etc/frr/ospfd.conf 
hostname anycastrouter
!
log file /var/log/frr/ospfd.log
!
interface dhcp
 ip ospf cost 10000 138.80.255.102
 ip ospf cost 10010 138.80.255.202
!
interface ens192
 ip ospf priority 0
 ip ospf authentication message-digest
 ip ospf message-digest-key 1 md5 ...
!
router ospf
 router-id 138.80.232.139
 passive-interface default
 no passive-interface ens192
 log-adjacency-changes
 network 138.80.232.128/26 area 0.0.0.0
 network 138.80.255.102/32 area 0.0.0.0
 network 138.80.255.202/32 area 0.0.0.0
 distribute-list ANYCAST out connected
!
access-list ANYCAST permit 138.80.255.0/24
!
line vty
!

You can see the costs on linux using the vtysh command:

root@dhcptst1 ~# vtysh

Hello, this is FRRouting (version 7.0).
Copyright 1996-2005 Kunihiro Ishiguro, et al.

dhcptst1.cdu.edu.au# show ip ospf interface 
dhcp is up
  ifindex 3, MTU 1500 bytes, BW 0 Mbit <UP,BROADCAST,RUNNING,NOARP>
  This interface is UNNUMBERED, Area 0.0.0.0
  MTU mismatch detection: enabled
  Router ID 138.80.232.139, Network Type BROADCAST, Cost: 10000
  Transmit Delay is 1 sec, State DR, Priority 1
  No backup designated router on this network
  Multicast group memberships: <None>
  Timer intervals configured, Hello 10s, Dead 40s, Wait 40s, Retransmit 5
    No Hellos (Passive interface)
  Neighbor Count is 0, Adjacent neighbor count is 0
  This interface is UNNUMBERED, Area 0.0.0.0
  MTU mismatch detection: enabled
  Router ID 138.80.232.139, Network Type BROADCAST, Cost: 10010
  Transmit Delay is 1 sec, State DR, Priority 1
  No backup designated router on this network
  Multicast group memberships: <None>
  Timer intervals configured, Hello 10s, Dead 40s, Wait 40s, Retransmit 5
    No Hellos (Passive interface)
  Neighbor Count is 0, Adjacent neighbor count is 0
ens192 is up
  ifindex 2, MTU 1500 bytes, BW 10000 Mbit <UP,BROADCAST,RUNNING,MULTICAST>
  Internet Address 138.80.232.139/26, Broadcast 138.80.232.191, Area 0.0.0.0
  MTU mismatch detection: enabled
  Router ID 138.80.232.139, Network Type BROADCAST, Cost: 10
  Transmit Delay is 1 sec, State DROther, Priority 0
  No backup designated router on this network
  Multicast group memberships: OSPFAllRouters
  Timer intervals configured, Hello 10s, Dead 40s, Wait 40s, Retransmit 5
    Hello due in 0.815s
  Neighbor Count is 8, Adjacent neighbor count is 1

See also the show ip ospf route command (trimmed to the relevant section):

dhcptst1.cdu.edu.au# show ip ospf route              
============ OSPF network routing table ============
...
N    138.80.255.102/32     [10000] area: 0.0.0.0
                           directly attached to dhcp
N    138.80.255.202/32     [10010] area: 0.0.0.0
                           directly attached to dhcp 
...

You can see here that the two anycast IP addresses being advertised are 138.80.255.102 and 138.80.255.202, with a cost of 10000 and 10010 respectively.

Ok, so how can we check the costing on our Cisco router?

Checking OSPF costs on cisco side

The command to use on the cisco device is show ip ospf rib

x1c1coresw1>show ip ospf rib 

            OSPF Router with ID (138.80.232.33) (Process ID 1)


                Base Topology (MTID 0)

OSPF local RIB
Codes: * - Best, > - Installed in global RIB

...
*>  138.80.255.102/32, Intra, cost 10001, area 0.0.0.0
      via 138.80.232.139, Vlan128
...
*>  138.80.255.202/32, Intra, cost 10011, area 0.0.0.0
      via 138.80.232.139, Vlan128

You can see here that my server on 138.80.232.139 is showing up as the router for the two anycast addresses, with a cost of 10001 and 10011 – the costs I am sending above but with 1 added on for the link cost.

Therefore everything is working nicely.

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