There are three routers connected together over a switch.

• Router 1 is an FRR router with interface IP 10.10.10.1 and Loopback 192.0.2.1
• Router 2 is a preconfigured router with interface IP 10.10.10.2 and Loopback 192.0.2.2
• Router 3 is a Mikrotik router with interface IP 10.10.10.3 and Loopback 192.0.2.3

You will configure Router 1 and Router 3 to get them to communicate over OSPF and share infrastructure info. Router 2 already has a running OSPF process and will not need to be configured. Router 1 and Router 3 do not have any IP address configuration so you will also need to configure them appropriately.

Start with the FRR Router (Router 1)

Enter the configuration mode

 config t 

Set the hostname

 hostname FRR-Router1 

Set the loopback IP

 
interface lo
 description Loopback interface
 ip address 192.0.2.1/32

Set the interface IP which is connected to the switch

interface eth0
 description link to Router2
 ip address 10.10.10.1/24
 no shut
exit
exit

ping 10.10.10.2

Ensure ping reachability is working before proceeding. Router 3 at this point is not reachable but you must be able to reach Router 2.

Enter the configuration mode and enable OSPF on eth0 and the loopback. First, we will set our router-id as follows:

config t
ip router-id 192.0.2.1

The below activates OSPF.

router ospf
 log-adjacency-changes
 area 0 authentication message-digest

Now configure OSPF on the ethernet interface to add it to Area 0. Notice we are using a password to secure our OSPF updates between the routers (Router 2 has this configured and you will do the same on Router 3)

interface eth0
 ip ospf area 0
 ip ospf authentication-key ospflab
 ip ospf authentication

Do the same on the loopback interface to allow it's IP to be included in area 0 updates.

interface lo
  ip ospf area 0
  exit
  exit ! To exit the command prompt

sh ip ospf neighbor 

You should see something like the below:

Neighbor ID     Pri State           Up Time         Dead Time Address         Interface                        
192.0.2.2         1 Full/DR         1m50s             39.631s 10.10.10.2      eth0:10.10.10.1  

This means that a neighbor with the IP 192.0.2.2 has been seen and full adjacency completed. What does the State: Full/DR mean?

 sh ip route 

You will receive output as below. Observe the Codes. Which routes have you received over OSPF?

FRR-Router1# sh ip route
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
       f - OpenFabric,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

O>* 0.0.0.0/0 [110/10000] via 10.10.10.2, eth0, weight 1, 00:05:50
O   10.10.10.0/24 [110/100] is directly connected, eth0, weight 1, 00:05:51
C>* 10.10.10.0/24 is directly connected, eth0, 00:07:45
O>* 172.16.0.0/13 [110/10000] via 10.10.10.2, eth0, weight 1, 00:05:50
O   192.0.2.1/32 [110/0] is directly connected, lo, weight 1, 00:06:31
C>* 192.0.2.1/32 is directly connected, lo, 00:07:50
O>* 192.0.2.2/32 [110/100] via 10.10.10.2, eth0, weight 1, 00:05:51

We will do the same on the Mikrotik router to configure the interface and loopback IP addresses.

Enter the configuration mode and enable OSPF on eth0 and the loopback:

/interface bridge
add name=loopback

/interface ethernet
set [ find default-name=ether1 ] comment="Link to Router2 and Router1"

/ip address
add address=10.10.10.3/24 interface=ether1 comment="Link to Router2 and Router1"
add address=192.0.2.3/32 interface=loopback comment="Loopback Interface"

The below command activates OSPF with router ID 192.0.2.3

/routing ospf instance
add name=ospf1 router-id=192.0.2.3 version=2

/routing ospf area
add instance=ospf1 name=area0

/routing ospf interface-template
add networks=10.10.10.3/24 area=area0 auth=simple auth-key=ospflab
add networks=192.0.2.3/32 area=area0 auth=simple auth-key=ospflab

Notice we have added the OSPF authentication key as was done for FRR.

The following command will show the OSPF neighbors

/routing/ospf/neighbor/print

You should see somethign similar to the below

You should see something similar to the below:

Flags: D - DYNAMIC; A - ACTIVE; c - CONNECT, o - OSPF
Columns: DST-ADDRESS, GATEWAY, DISTANCE
    DST-ADDRESS    GATEWAY            DISTANCE
DAo 0.0.0.0/0      10.10.10.2%ether1       110
DAc 10.10.10.0/24  ether1                    0
DAo 172.16.0.0/13  10.10.10.2%ether1       110
DAo 192.0.2.1/32   10.10.10.1%ether1       110
DAo 192.0.2.2/32   10.10.10.2%ether1       110
DAc 192.0.2.3/32   loopback                  0

to ping on the Mikrotik, do as follows

/ping 192.0.2.1

The above will ping the loopback on Router 1. The route is available on OSPF

Now go back to the FRR router and see if there are new OSPF neighbors.

There are three routers connected together over a switch and with OSPF sending infrastructure prefix routes. All routers are part of Autonomouse System Number 64500. Here is a summary of the BGP related advertisements to be made within this IBGP. setup.

• Router 1 is an FRR router. It will advertise the prefix 198.51.100.0/24
• Router 2 is a preconfigured and is advertising the prefix 1.1.1.0/24
• Router 3 is a Mikrotik router. It will advertise the prefix 3.3.3.0/24

You will configure Router 1 and Router 3 to accept the BGP routes being advertised by all routers in AS 64500 and also configure the two routers to advertise their respective prefixes.

The following config is to activate BGP and setup the respective neighbours.

The follwing commands configure BGP on most Cisco and FRR routers.

router bgp 64500
 bgp log-neighbor-changes
 no bgp default ipv4-unicast
 neighbor 192.0.2.2 remote-as 64500
 neighbor 192.0.2.2 description to Router 2
 neighbor 192.0.2.3 remote-as 64500
 neighbor 192.0.2.3 description to Router 3
 !
 address-family ipv4 unicast
  network 198.51.100.0/24
  neighbor 192.0.2.2 activate
  neighbor 192.0.2.2 soft-reconfiguration inbound  
  neighbor 192.0.2.2 prefix-list ROUTER2-IN in
  neighbor 192.0.2.2 prefix-list ROUTER2-OUT out
  neighbor 192.0.2.3 activate
  neighbor 192.0.2.3 soft-reconfiguration inbound  
  neighbor 192.0.2.3 prefix-list ROUTER3-IN in
  neighbor 192.0.2.3 prefix-list ROUTER3-OUT out
  
 exit-address-family
exit

Let us look at what each command means:

You need to control what your router accepts and advertises and BGP. This is done by having a policy for incoming traffic and outgoing traffic for each BGP peer. We will start by doing a policy for advertisements received and sent to Router 2:

You have the above command in the previous BGP configuration:

“neighbor 192.0.2.2 prefix-list ROUTER2-IN in” .

The below is the actual policy enforcement using the prefix list statement:

ip prefix-list ROUTER2-IN seq 5 permit 1.1.1.0/24
ip prefix-list ROUTER2-IN seq 10 deny 0.0.0.0/0 le 32

The first line allows the incoming prefix being advertised by Router 2 which is 1.1.1.0/24. The second line denies any further BGP advertisements to be accepted from Router 2. This is important to ensure strict BGP traffic control.

The same must be done for Router 3.

ip prefix-list ROUTER3-IN seq 5 permit 3.3.3.0/24
ip prefix-list ROUTER3-IN seq 10 deny 0.0.0.0/0 le 32

This enforces that only the prefix 3.3.3.0/24 is accepted from Router 3.

You must also be strict on what BGP advertisement your router sends out. The lines below ensure that you only advertise the prefix 198.51.100.0/24 to Router 2 and Router 3

ip prefix-list ROUTER2-OUT seq 5 permit 198.51.100.0/24
ip prefix-list ROUTER2-OUT seq 10 deny 0.0.0.0/0 le 32

ip prefix-list ROUTER3-OUT seq 5 permit 198.51.100.0/24
ip prefix-list ROUTER3-OUT seq 10 deny 0.0.0.0/0 le 32

Your router will advertise the prefix 198.51.100.0/24. To do so, this route must exist in the router's routing table via other protocols or manually inserted. We will manually add it for this lab exercise:

config t
ip route 198.51.100.0/24 eth0
exit

Try the following commands and assess the output:

•  sh ip bgp neighbors 

  to see BGP neighbours

•  sh ip bgp neighbor 192.0.2.2 advertised-routes 

  to see routes sent to this neighbor

•  sh ip bgp neighbor 192.0.2.2 recived-routes 

  to see routes received from this neighbor

•  sh ip route 

  To see the router's routing table. Look for the BGP codes

The following config is to activate BGP and setup the respective neighbours.

The follwing commands configure BGP on most Mikrotik version 7 routers.

/routing bgp connection
add address-families=ip as=64500 connect=yes disabled=no input.affinity=alone .filter=ROUTER2-IN \
    listen=yes local.address=192.0.2.3 .role=ibgp name=To-ROUTER2 output.affinity=alone \
    .default-originate=never .filter-chain=ROUTER2-OUT .network=bgp-networks remote.address=\
    192.0.2.2 .as=64500 router-id=192.0.2.3 routing-table=main

add address-families=ip as=64500 connect=yes disabled=no input.affinity=alone .filter=ROUTER1-IN \
    listen=yes local.address=192.0.2.3 .role=ibgp name=To-ROUTER1 output.affinity=alone \
    .default-originate=never .filter-chain=ROUTER1-OUT .network=bgp-networks remote.address=\
    192.0.2.1 .as=64500 router-id=192.0.2.3 routing-table=main
    

Let us look at what the configuration means for each key word:

For Mikrotik, the following specifies the inbound policy for each BGP peer (Router 1 and Router 2)

/routing filter rule
add chain=ROUTER1-IN rule="if (dst in 198.51.100.0/24) { accept } else { reject }"
add chain=ROUTER2-IN rule="if (dst in 1.1.1.0/24) { accept } else { reject }"

The following specifies the outbound policy for each BGP peer (Router 1 and Router 2). This is to permit which prefixes the Mikrotik router will advertise to Router 1 and Router 2:

/routing filter rule
add chain=ROUTER2-OUT rule="if (dst in 3.3.3.0/24) { accept } else { reject }"
add chain=ROUTER1-OUT rule="if (dst in 3.3.3.0/24) { accept } else { reject }"

Your router will advertise the prefix 3.3.3.0/24. To do so, this route must exist in the router's routing table via other protocols or manually inserted. We will manually add it for this lab exercise. For Mikrotik, this involves adding a firewall statement:

/ip firewall address-list
add address=3.3.3.0/24 list=bgp-networks

And also add the route itself into the routing table with the below command:

/ip route
add blackhole dst-address=3.3.3.0/24

Recall that in the bgp configuration earlier, we had this statement for each BGP peer: “.network=bgp-networks”. That enables the Mikrotik router to advertise the prefixes included in the firewall list with the name “bgp-networks”. That is all that is needed, now we can test BGP.

Check which prefixes your Mikrotik router is sending out:

/routing bgp advertisements print

You should see something like this:

Check which routes are in the routing table and see if your are receiveing routes from Router 1 and Router 2:

/ip route print

Do you see the routes indicated in red below? If so, you are receiving BGP correctly:

• DAb 1.1.1.0/24 192.0.2.2 200
• DAb 198.51.100.0/24 192.0.2.1 200

Try the following commands to see more info on BGP:

•  /routing ospf neighbor print

  to see BGP neighbours

•  /routing/bgp/session/print 

  to see more info on the BGP sessions

Do the following on Mikrotik to see if the BGP full mesh is working:

• Check what you are receiving from Router 3:

  sh ip bgp neighbors 192.0.2.3 received-routes 

• Check the routing table

  sh ip route

You should see something like the below. Do you see the routes indicated with “B”?

Congratulations, you have configured a BGP full mesh in a multi-vendor network.