Junos Basics – Single Area OSPF

In my previous Junos Basics post I covered a simple VRRP configuration in Junos. In this post I’ll run through a basic OSPF configuration on a pair of Juniper routers.

Here’s our network:

Objectives:

• Establish an OSPF neighbour relationship between R1 and R2
• increase security by using md5 authentication
• Configure all router interfaces to be part of OSPF area 0.0.0.0
• Make interaces e1 and e2 passive for OSPF on each router

First of all, we’ll put the IP addresses onto each interface. Here’s R1’s config:

set interfaces em0 unit 0 family inet address 192.168.0.1/30
set interfaces em1 unit 0 family inet address 10.0.0.1/24
set interfaces em2 unit 0 family inet address 10.0.1.1/24

Here’s R2’s interface configuration and confirmation of IP connectivity to R1:

set interfaces em0 unit 0 family inet address 192.168.0.2/30
set interfaces em1 unit 0 family inet address 10.0.2.1/24
set interfaces em2 unit 0 family inet address 10.0.3.1/24

root> ping 192.168.0.1
PING 192.168.0.1 (192.168.0.1): 56 data bytes
64 bytes from 192.168.0.1: icmp_seq=0 ttl=64 time=0.206 ms
64 bytes from 192.168.0.1: icmp_seq=1 ttl=64 time=0.405 ms

Next, we configure interface em0 on each router to be in OSPF area 0.0.0.0 and to use md5 authentication with a key of “juniper”:

[edit protocols ospf]
root# set area 0.0.0.0 interface em0 authentication md5 1 key juniper

Verify we now have a neighbour relationship formed between R1 and R2:

root@R1> show ospf neighbor
Address          Interface              State     ID               Pri  Dead
192.168.0.2      em0.0                  Full      10.0.2.1         128    37

root@R2> show ospf neighbor
Address          Interface              State     ID               Pri  Dead
192.168.0.1      em0.0                  Full      10.0.0.1         128    30

Next, we’ll configure the other interfaces on each router so that the networks they are attached to are advertised into OSPF area 0.0.0.0, but no neighbour relationships can form over them (passive):

set protocols ospf area 0.0.0.0 interface em1 passive
set protocols ospf area 0.0.0.0 interface em2 passive

If we verify the OSPF interface configuration on R2, we can also see that R2 has won the election process to become the Designated Router (DR) for area 0.0.0.0:

root@R2> show ospf interface
Interface           State   Area            DR ID           BDR ID          Nbrs
em0.0               DR      0.0.0.0         10.0.2.1        10.0.0.1           1
em1.0               DRother 0.0.0.0         0.0.0.0         0.0.0.0            0
em2.0               DRother 0.0.0.0         0.0.0.0         0.0.0.0            0

Next, we’ll take a look at R2’s OSPF routing table and check it contains routes to R1’s attached networks:

root@R2> show ospf route
Topology default Route Table:

Prefix             Path   Route       NH   Metric  NextHop       Nexthop
                   Type   Type        Type         Interface     addr/label
10.0.0.1           Intra  Router      IP        1  em0.0         192.168.0.1
10.0.0.0/24        Intra  Network     IP        2  em0.0         192.168.0.1
10.0.1.0/24        Intra  Network     IP        2  em0.0         192.168.0.1
10.0.2.0/24        Intra  Network     IP        1  em1.0
10.0.3.0/24        Intra  Network     IP        1  em2.0
192.168.0.0/30     Intra  Network     IP        1  em0.0

One other useful verification command displays the OSPF Link State Database:

root@R2> show ospf database

    OSPF database, Area 0.0.0.0
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router   10.0.0.1         10.0.0.1         0x8000000b   332  0x22 0x2adb  60
Router  *10.0.2.1         10.0.2.1         0x8000000a   325  0x22 0x827b  60
Network *192.168.0.2      10.0.2.1         0x80000003  2514  0x22 0x3476  32

I hope this has been a useful explanation.  In my next Junos Basics post I’ll cover configuring an EX2200C switch as a DHCP server.

Thanks for reading.

Rich

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