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Hans van Kranenburg 2015-06-07 03:12:18 +02:00
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ospf-intro/README.md
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@ -351,7 +351,7 @@ When I disabled the interface on R5, BIRD on R5 got notified by netlink that the
Apparently, I lost a ping while the network was busy to get into a stable converged state again. ;-(
The second thing I want to point out is about the /32 addresses on the loopback interfaces of the routers. I figure you might be wondering what they're useful for. Well, normally, a /32 address on a network interface would not make much sense. But image what happens when we include it in our OSPF process... It suddenly becomes a network subnet whose reachibility information is propagated throughout the whole network. Ok, this subnet can only contain a single address, but it's a perfect way to make sure that if any path exists to this single router in the network, OSPF will make you able to use it to connect to the router. So, if I'm the network administrator of the example network we've just built, and `10.50.1.12` is my workstation, I can use `10.9.9.5` to connect to, for example with SSH, to manage this router. Een when I accidentally would disable the link to the `10.1.2.0/24` network, my SSH session would simply stay active, the traffic to and from R5 being rerouted via R1 back to my workstation... :-D Later on, in the BGP tutorial we'll see that there are actually other routing protocols that rely on this mechanism to function correctly.
The second thing I want to point out is about the /32 addresses on the loopback interfaces of the routers. I figure you might be wondering what they're useful for. Well, normally, a /32 address on a network interface would not make much sense. But image what happens when we include it in our OSPF process... It suddenly becomes a network subnet whose reachability information is propagated throughout the whole network. Ok, this subnet can only contain a single address, but it's a perfect way to make sure that if any path exists to this single router in the network, OSPF will make you able to use it to connect to the router. So, if I'm the network administrator of the example network we've just built, and `10.50.1.12` is my workstation, I can use `10.9.9.5` to connect to, for example with SSH, to manage this router. Even when I accidentally would disable the link to the `10.1.2.0/24` network, my SSH session would simply stay active, the traffic to and from R5 being rerouted via R1 back to my workstation... :-D Later on, in the BGP tutorial we'll see that there are actually other routing protocols that rely on this mechanism to function correctly.
## Next...
@ -363,4 +363,4 @@ First of all, don't forget to take a look at the BIRD documentation about OSPF.
* Equal cost multipath routing (ECMP) is a big thing nowadays, which is used a lot to load balance traffic over multiple paths to a destination instead of choosing only one as best path. You can even enable that in the network we just built by just specifying `ecmp yes` in the OSPF configuration and see what effect it has on the output of `ip r` on the linux command line. Just search for information on it on the Internet to learn more.
* 'Cost' is an aspect that is fundamental to OSPF and the calculation of the shortest paths in the network. Traditionally, cost is related to the bandwith of a link between routers, and causes higher bandwith connections to be prefered above lower bandwith connections. Since we're working with switched Gigabit/s networks by default now, if it's not 10Gb/s, in the datacenter and even in our office, I've just been ignoring that.
Well, after completing this tutorial, I also encourage you to start reading the other "An Introduction to OSPF" like pages on the internet, since they should be a lot easier to understand while having seen it work for real! :D
Well, after completing this tutorial, I also encourage you to start reading the other "An Introduction to OSPF" like pages on the internet, since they should be a lot easier to understand while having seen it work for real! Have fun.