Routing

By default, the Router ID of an OSPF enabled router is set by the highest address of any online loopback interfaces, or failing that the highest address of any up physical interfaces. The router ID is selected when the OSPF process initialises, and does not change until the the process has been restarted. The entire…

OSPF can be enabled on a router via two methods, a network statement or via interface specific configuration. OSPF Network Statements Entering an OSPF network statement into the router configuration will try match the interfaces that will partake in the OSPF process by their primary interface addresses. Secondary addresses on an interface can be inserted…

In some networks that are not point to point, such as Ethernet LANs and Frame Relay, there can be more than two routers that can exist in a single segment. Without any control system in place, scalability issues could arise with the more routers that partake in OSPF on the subnet – more network traffic,…

An OSPF neighbour is another router that shares an OSPF enabled link with the local router. OSPF can discover other routers on shared links with OSPF hello packets, an adjacent OSPF neighbour shares a synchronised database between the two routers. The OSPF process on a router will maintain a list of OSPF neighbours and their…

The OSPF router ID, or RID, is a 32 bit number that identifies the OSPF router. This router ID is required to be unique for each OSPF process in the OSPF domain, and also unique between OSPF processes on a router.

OSPF Hello packets discover and maintain relationships with neighbouring OSPF routers. Hello packets in most default configurations send to the multicast address 224.0.0.5 Data Field Description Router ID A unique 32-bit ID within the OSPF domain Authentication Options Allows secured communications between OSPF routers. Can be set to: none, clear text or MD5 authentication Area…

OSPF runs directly on IPv4, using it’s own protocol numbered 89, reserved for OSPF by IANA (Internet Assigned Numbers Authority). OSPF uses multicast where possible to reduce unnecessary broadcast or unicast traffic: Multicast address 224.0.0.5 or MAC 01:00:5E:00:00:05. All Routers using OSPF receive these packets. Multicast address 224.0.0.6 or MAC 01:00:5E:00:00:06. Only designated routers receive…

OSPF, or Open Shortest Path First is a link state routing protocol. It is a non proprietary Interior Gateway Protocol. OSPF version 2 is defined in RFC 2328 and supports IPv4. OSPF version 3 is defined in RFC 5340 and supports IPv6 OSPF works by sending neighbouring routers link state advertisements (LSAs) that contain the…

To scale an EIGRP system effectively, it requires summarisation. EIGRP can summarise network prefixes on an interface basis. Prefixes contained within the summarisation are suppressed with the summary route being advertised instead, although the summary route is only advertised if a suppressed prefix is valid within the summary route. Route summarisation also creates a query…

Hello and Hold Timers An EIGRP hello packet is not just for forming new adjacencies, but is used for checking that the neighbour is working and responsive. By default EIGRP hello packet is sent out every 5 seconds, or 60 seconds on a slow speed interface (T1 or lower) EIGRP uses a timer called a…