OSPF should aggregate route entries from the backbone area into a non-backbone area or from a non-backbone area into the backbone area. Route aggregation works only on the ABR.User can use the "
advertise disable" parameter to restrain route aggregation at the ABR. The ABR will aggregate routes by default after area-range is configured and the packet is routed to the best (the longest or most specific) match.
To disable injecting routes into an area from an ABR manually, the user can apply the prefix lists in inbound or outbound directions to control the dissemination of routes into and out of OSPF areas. The command used to control route dissemination is set protocols ospf area in filter-list prefix. The keyword in indicated routes advertised into an area. Whereas out indicates routes going out of the area. Its important to note that the user must configure the prefix list before applying it through the set protocols ospf area in filter-list prefix command. The command to create the prefix list is set routing prefix-list.
Figure 5-6. OSPF area range configuration.
Configuring Switch A
...
Figure 5-6 shows a sample OSPF topology with three different areas configured. In this example we will focus on the configuration on Router 2 to see how it affects the routing table on Router 1 which is in area 0.0.0.2. First we will see the configuration on Router 2.
Configuring Router 2
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admin@router2# set interface gigabit-ethernet ge-1/1/3 family ethernet-switching native-vlan-id 30 admin@router2# set interface gigabit-ethernet tege-1/1/495 family ethernet-switching native-vlan-id 500 admin@XorPlus# 40 admin@router2# set protocols lldp enable true admin@router2# set protocols ospf4ospf router-id 12.12.12.12 admin@XorPlus#admin@router2# set protocols ospf4ospf area 0.0.0.0 interface vlan-500 vif vlan-500 address 192.168.1.2 admin@XorPlus#commit Waiting for merging configuration. Commit OK. Save Done. admin@XorPlus# |
Configuring Switch B
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admin@XorPlus# set vlans vlan-id 500 l3-interface vlan-500 admin@XorPlus# set vlan-interface interface vlan-500 vif vlan-500 address 192.168.1.1 prefix-length 30 admin@XorPlus# set interface gigabit-ethernet te-1/1/49 family ethernet-switching native-vlan-id 500 admin@XorPlus# set protocols ospf4 router-id 4.4.4.4 admin@XorPlus# set protocols ospf4 area 0.0.0.0 interface vlan-500 vif vlan-500 address 192.168.1.1 admin@XorPlus#2 area-type "stub" admin@router2# set protocols ospf area 0.0.0.1 in filter-list admin@router2# set protocols ospf network 10.10.2.0/24 area 0.0.0.2 admin@router2# set protocols ospf network 10.10.4.0/24 area 0.0.0.0 admin@router2# set system hostname "router2" admin@router2# set l3-interface loopback lo address 2.2.2.2 prefix-length 32 admin@router2# set l3-interface vlan-interface vlan30 address 10.10.2.2 prefix-length 24 admin@router2# set l3-interface vlan-interface vlan40 address 10.10.4.1 prefix-length 24 admin@router2# set vlans vlan-id 40030 l3-interface vlan-400 admin@XorPlus#"vlan30" admin@router2# set vlan-interfacevlans interface vlan-400id vif40 vlanl3-400 address 172.25.150.250 prefix-length 30 admin@XorPlus# set interface gigabit-ethernet te-1/1/50 family ethernet-switching native-vlan-id 400 admin@XorPlus# set protocols ospf4 area 1.1.1.1 interface vlan-400 vif vlan-400 address 172.25.150.250 admin@XorPlus#commit Waiting for merging configuration. Commit OK. Save Done. admin@XorPlus# |
Configuring Switch C
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admin@XorPlus# set vlans vlan-id 400 l3-interface vlan-400
admin@XorPlus# set vlan-interface interface vlan-400 vif vlan-400 address 172.25.150.249 prefix-length 30
admin@XorPlus# set interface gigabit-ethernet te-1/1/49 family ethernet-switching native-vlan-id 400
admin@XorPlus# set protocols ospf4 router-id 3.3.3.3
admin@XorPlus# set protocols ospf4 area 1.1.1.1 interface vlan-400 vif vlan-400 address 172.25.150.249
admin@XorPlus#commit
Waiting for merging configuration.
Commit OK.
Save Done.
admin@XorPlus# |
Checking the route table on Switch C
There will be a 30-bit route entry,192.168.1.0/30.
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admin@Xorplus# run show route forward-route ipv4 all
Destination NextHopMac Port
--------------- ----------------- ---------
172.25.150.248/30 60:EB:69:44:44:44 connected
192.168.1.0/30 A8:2B:B5:E0:94:A7 te-1/1/49
Total route count:2 |
Configuring area-range on ABR(Switch B)
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admin@XorPlus# set protocols ospf4 area 0.0.0.0 area-range 192.168.1.0/24 advertise true admin@XorPlus# commit Waiting for merging configuration.interface "vlan40" |
Check the Routing Table on Router 1
If we check the routing table on Router 1, we can see prefix 10.10.5.0 is in the routing table advertised through OSPF.
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admin@router1> show route ipv4
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, D - SHARP,
F - PBR, f - OpenFabric,
> - selected route, * - FIB route, q - queued route, r - rejected route
O 0.0.0.0/0 [110/11] via 10.10.2.2, vlan10, weight 1, 04:01:47
O 1.1.1.1/32 [110/0] is directly connected, lo, weight 1, 04:03:37
C>* 1.1.1.1/32 is directly connected, lo, 04:03:37
O>* 4.4.4.4/32 [110/20] via 10.10.2.2, vlan10, weight 1, 00:00:02
O 10.10.2.0/24 [110/10] is directly connected, vlan10, weight 1, 04:02:37
C>* 10.10.2.0/24 is directly connected, vlan10, 04:02:37
O>* 10.10.4.0/24 [110/20] via 10.10.2.2, vlan10, weight 1, 00:00:02
O>* 10.10.5.0/24 [110/30] via 10.10.2.2, vlan10, weight 1, 00:00:02 |
Now we will add the commands set protocols ospf area 0.0.0.2 in filter-list prefix list1 and set routing prefix-list IPv4 list1 deny prefix 10.10.5.0/24
to Router 2.
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admin@router2# set routing prefix-list IPv4 list1 deny prefix 10.10.5.0/24 admin@router2# set protocols ospf area 0.0.0.2 in filter-list prefix "list1" Commit OK. Save doneDone. admin@XorPlus# |
Checking the route table on Switch C
The route entry 192.168.1.0/30 will be replaced by 192.168.1.0/24.
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admin@Xorplus# run show route forward-route ipv4 all Destination admin@router2# |
Now if we check the routing table on Router 1 again, we see the prefix 10.10.5.0/24 has disappeared from the routing table.
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admin@router1> show route ipv4 Codes: K - kernel route, C - connected, S - static, R - RIP, NextHopMac O - OSPF, I - IS-IS, B - PortBGP, E - EIGRP, N - NHRP, T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP, F -------- PBR, f - OpenFabric, > - selected route, * - FIB route, q --------------- --------- 172.25.150.248/30 60:EB:69:44:44:44 connected 192.168.1.0/24 A8:2B:B5:E0:94:A7 te-1/1/49 Total route count:2 queued route, r - rejected route O 0.0.0.0/0 [110/11] via 10.10.2.2, vlan10, weight 1, 04:54:16 K>* 0.0.0.0/0 [0/0] via 10.10.51.1, eth0, 04:56:35 O 1.1.1.1/32 [110/0] is directly connected, lo, weight 1, 04:56:06 C>* 1.1.1.1/32 is directly connected, lo, 04:56:06 O 10.10.2.0/24 [110/10] is directly connected, vlan10, weight 1, 04:55:06 C>* 10.10.2.0/24 is directly connected, vlan10, 04:55:06 |