gi 0/0is connected to the client pc
gi x/0is connected to a corresponding router. There may be more than one interface.
/28IPv4 address space listed for you, subnet your address space such that you have:
/29for the link between you and your PC
/32to be used as your router's loopback interface.
/60IPv6 address space listed for you, subnet your address space such that you have:
/64to be used for Loopbacks (your router only needs one /128)
/64to be used for the link between your client PC and your router.
2001:43f8:220:ffd0::/60these will be:
2001:43f8:220:ffd0::1/128for the router
2001:43f8:220:ffd1::/64for the point-to-point between the PC and the router
Enter OSPF configuration mode. The 1 is simply the OSPF process ID - a router can run more than one OSPF process if required. Note that process IDs do not even have to match between routers in the same area.
The network statement has two functions and its use varies depending on the function required.
The first use is to enable OSPF on all interfaces which match the given IP address + "wildmask". A wildmask is used in access control lists to select a range of addresses. A "0" bit in the wildmask means the corresponding address bit must match, and a "1" means the corresponding address bit is "don't care". Examples:
network 184.108.40.206 0.0.0.0 area 0 network 220.127.116.11 0.0.0.0 area 0 -- talk OSPF only on those interfaces with these addresses network 18.104.22.168 0.0.0.3 area 0 -- talk OSPF on the serial interface with this address (this is an alternative to the previous examples and has the same functionality) network 22.214.171.124 0.0.0.255 area 0 -- talk OSPF on every interface whose IP address is 196.200.220.X network 0.0.0.0 255.255.255.255 area 0 -- talk OSPF on every interface we have
By talking OSPF on an interface the router will automatically inject the network block used on that interface into OSPF.
Note that it is important that we only talk OSPF to our own networks, never to customers or other ISPs (they could break our network by injecting bad information), so usually it is best just to list the interfaces we want to talk on.
The second use of the network statement is to inject prefixes into OSPF. For this function the network statement must match both the network and the network's mask on that interface. The mask is called an "inverse mask", and is the one's complement of the network mask for the network block. This technique is used to inject prefixes from non-OSPF speaking interfaces into OSPF.
network 126.96.36.199 0.0.0.3 area 0 -- announce the network 188.8.131.52/30 to OSPF network 184.108.40.206 0.0.0.255 area 0 -- announce the network 220.127.116.11/24 to OSPF
Advertise all networks to which we are connected, including those which are not being used to talk to other OSPF routers. The use of this command is not recommended within ISP backbones, but is included here for completeness.
("redistributed connected" by itself only distributes classful routes, i.e. whole class A/B/C networks, so it's important to add "subnets")
Advertise all static routes we have (except defaultroute). The use of this command isn't ordinarily required or recommended. However, there will be circumstances where redistribution of statics into OSPF are required. An example will be shown in the lab.
Advertise a default route into OSPF, with a cost of "n". Typically this would go on your border router(s). Without 'always', the announcement will only be made if the router already has a valid defaultroute from somewhere else (e.g. a static route to a link which is up)
Use MD5 authentication on all OSPF packets
ip ospf cost <n> Set outbound interface cost ip ospf message-digest-key 1 md5 <string> Set MD5 authentication key
A loopback interface is a single (/32) IP address which belongs to a device, independent of its physical interface addresses. It's very convenient when managing routers, because you can use the loopback address as a fixed address to telnet to, or monitor using SNMP, which will continue to work even if one or more of the interfaces has failed.
router-a#conf t router-a(config)#no router ospf 1 router-a(config-if)# [Hit ctrl-Z] router-a#write mem
router-a#show ip route The only routes you should see are (C)onnected routes for your own interfaces. If you have any (S)tatic routes, delete them like this: router-a#conf t router-a(config)#no ip route 18.104.22.168 255.255.255.240 22.214.171.124 router-a(config-if)# [Hit ctrl-Z] router-a#write mem
(Your PC won't be able to ping any other PCs though, because your router doesn't have the routes any more)
You will need to subdivide your assigned network space. You will need one subnet for your desk network, and a /32 for the loopback. (In real life you would have a number of routers, and say a /29 block would be enough for 8 loopbacks). Configure your loopback address into your router.
The example below is for the router belonging to Team A. They have decided to subdivide their address block 126.96.36.199/28 such that 188.8.131.52/32 is the address of the loopback interface of their router.
router-a#conf t router-a(config)#int loopback0 router-a(config-if)#ip address 184.108.40.206 255.255.255.255 router-a(config-if)# [Hit ctrl-Z]
The network topology is the same as for the static routing exercise
We will use a feature introduced in IOS 12.0 which explicitly disables OSPF on all interfaces except those you nominate.
router-a#conf t router-a(config)#router ospf 1 router-a(config-router)#log-adjacency-changes router-a(config-router)#passive-interface default router-a(config-router)#no passive-interface gi1/0 router-a(config-router)#network 220.127.116.11 0.0.0.31 area 0 ! backbone router-a(config-router)#network 18.104.22.168 0.0.0.0 area 0 ! loopback router-a(config-router)#network 22.214.171.124 0.0.0.7 area 0 ! gi0/0subnet router-a(config-router)# [Hit ctrl-Z]
router-a(config)#router ospf 1 router-a(config-router)#area 0 authentication message-digest router-a(config-router)#int gi1/0 router-a(config-if)#ip ospf message-digest-key 1 md5 afnog router-a(config-if)#ip ospf cost 100 router-a(config-if)# [Hit ctrl-Z]
In real life you should use an MD5 key which is different from your login, enable and SNMP strings
router-a#show ip ospf int router-a#show ip ospf neighbor
To interpret the neighbor information:
2WAY = we are neighbors (we have established 2-way exchange of hellos), but neither of us is a designated router FULL = we are neighbors and we exchange routes (one of us is DR or BDR) DR = we are the Designated Router for this network BDR = we are the Backup Designated Router for this network DROTHER = we are neither DR nor BDR
If you see other states, they are intermediate steps on the way to establishing the final relationship, and should change after a few seconds.
DR = BDR =
router-a#show ip route
Routes learned through OSPF are tagged with O. Check that the next hop IP address for each route is correct
Also, the far router should also have picked up your route. You can go over to the other desk and ask to see "show ip route"
$ ping 126.96.36.199 ...
We are now going to take the above topology and enable IPv6 on it.
ipv6 router ospf 1
We also need to mark all interfaces passive by default, as we did for OSPFv2 (for IPv4 above), and then activate the ones we will talk OSPFv3 over. For example:
ipv6 router ospf 1 log-adjacency-changes passive-interface default no passive-interface gi1/0
interface gigabitethernet 1/0 ipv6 address 2001:43f8:220:ff00::1/64
Configure addresses on the active interfaces on the router. You will need one /64 for the link to your PC, one /128 for the loopback interface, and of course an address on the backbone network.
interface gigabitethernet 0/0 ipv6 router ospf 1 area 0
So this example says that we are going to run OSPFv3 on GigabitEthernet 0/0, and that this interface will be in area 0. It also says that the IPv6 address/subnet configured on GigabitEthernet 0/0 will be automatically inserted into the OSPFv3 routing table.
Interfaces which are marked as passive in the generic OSPFv3
configuration but have the
ipv6 router ospf 1 area0
marked on the interface will simply have their configured IPv6
network address being inserted into the OSPFv3 routing table.