Archives for category: routing protocol

OSPF is used in numerous networks, it is well documented, well-known and widely tested in many scenarios. When IPv6 came along, good old OSPF which was used for IPv4 (OSPFv2), got a younger brother – OSPFv3. Many networks now run both protocols, one for IPv4 and the other for IPv6. This is getting more and more ridiculous, because OSPFv3 can be used to route IPv4 also.

See how this can be done with Cisco IOS and Juniper JUNOS. Read the rest of this entry »

A very simple question with a tricky answer ;-). How many OSPF areas are in this network?

For OSPF, areas are contiguous segments of networks and routers. One of the golden rules of standard area design is that all OSPF areas must have a connection to the backbone area (area 0). A simple topology that shows area 100 connected to the backbone is depicted below:


How many OSPF areas are there in all? Read the rest of this entry »

I’ve found one of the best answers to the question “What is BGP for?” in one of Philip Smith’s presentations (google for “BGP Best Current Practices”): “What is an IGP not for?”

Internal Routing Protocols (IGPs), like IS-IS and OSPF, are used to maintain infrastructure connectivity. They carry infrastructure addresses and are designed for rapid convergence within reasonably sized and manageable routing domains. On the other hand, BGP is designed primarily as a routing policy tool. External BGP carries Internet prefixes and exchanges them between autonomous systems according to some policy and rules of good behaviour. BGP is also used internally to carry customer prefixes and adds full flexibility to the routing decisions. BGP can handle huge routing tables, but in a somehow stable environment. It is designed to scale with expanding networks but not to respond quickly to topology changes. Read the rest of this entry »

The devil is in the detail.

Recently I’ve taken a part in some OSPFv3 troubleshooting. It was a simple setup and the problem was soon reduced to just two adjacent routers, both running OSPF for IPv6. A simplified schema describes the situation:

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