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I can't wrap my head around routing tables. Is it true that every router has a table with routes to every ip address in the world? Wouldn't that make the tables huge and thus make the lookup slow?
Routers with few interfaces need only few entries - a home router with a single subnet inside and the Internet outside just requires two entries.
Routing is a distributed job, every router only needs to know the routes it's got connected somewhere. Hops more remote to the final destination might only match a very short prefix - the default route with /0, or maybe /8 or /12 specific routes. The closer a hop is to the destination, the more refined (=longer prefix) the route is likely to get, with a prefix of /24, /29 or even /32.
The more interfaces, subnets and thus choices a router has got, the longer the routing table gets. Internet core routers may have many 100,000 to more than a million routing entries (thx Ron). More powerful routers use special, content-addressable memory (TCAM) to enable single-step lookup.
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The picture below sums up my home network. I have two routers and want to split things up a bit (I have my reasons and don't want an access point). I'm a data guy and not a network guy so apologies ahead of time for what may be a trivial question.
Without the static routes, computers hooked up to router 'B' were able to get out to the internet, but I want computers on Router 'A' to be able to communicate to computers attached router 'B' (and vice versa). With the static routes on each router, I still couldn't communicate from A --> B, but only when I added routes on the computer themselves (Mix of Ubuntu and Windows) could I get it to work.
Example: Computer on 'A' needed a route to 192.168.2.0/24 via 192.168.1.10 to be able to ping the computer on 192.168.2.x, though it was able to ping the gateway (192.168.2.1) prior to the route addition.
NOTE: Router 'A' is a TPlink and Router 'B' is an Engenius (with only 1 port, no lan/wan option)
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Whats the difference bewteen a GSLB and ADC. I can see that both can do load balancing, but i want to know the difference and additional functionalities each can perform. And i'd also want to know if one can replace the other.
GSLB is a general Term: Global Server Load Balancing
ADC is a Citrix product which does GSLB as well as proxying traffic.
To replace an ADC deployment, which saves f**king money(man they charge lots for it),
the proxy part can be replaced with NGINX + Server, the GSLB(which is just DNS with healthchecks) can be replaced with BIND(which actually runs on ADC as a service) and healthckeck to the backend server to remove/add record to DNS.
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Obviously the difference is that one can and one cannot access Netflix. But how does Netflix ban VPNs while not catching VPNs designed specifically to access Netflix?
The main difference is the question of whether Netflix knows about them yet or not.
In time, the VPNs which can access Netflix today will likely end up being blocked by from accessing the service when Netflix's analysis of incoming connections reveals IP addresses which could belong to VPNs used to circumvent their restrictions.
It is possible that some operators of VPN services may make use of IP addresses which are changed periodically to make detection less likely and this is how they may go for an extended period of time without being blocked.
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I am studying networking and operating systems and I stumbled upon this statement:
If there is no default gateway in the routing table we can't transfer packets to all the addresses.
I am asking whether the above statement is correct?
Yes the statement is true. Here is the definition from wikipedia
A default gateway in computer networking is the node that is assumed
to know how to forward packets on to other networks. Typically, in a
TCP/IP network, nodes such as servers, workstations and network
devices each have a defined default route setting, (pointing to the
default gateway), defining where to send packets for IP addresses for
which they can determine no specific route.
A routing table can not store information of all the possible routes to which the computer may connect. So it needs a default mechanism to send traffic to computers for which no known path exists. The way is to route all such packets to default gateway.
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I have recently added a dlink router to my existing network, and connected some computers with it. The existing network uses ip range 192.168.1.x and the new router uses 192.168.0.x. Internet services is accessible on both the networks, but a shared resource or a web server connected to one network is not accessible to the systems of other network.
I googled this issue but I am unable to resolve the issue, please help.
If you are just going to be using the router as a switch on an existing network, you need to turn off its router-y features.
Go onto the web interface of the device and turn of "NAT", that way they'll use the same address space as everything else on the network.
They'll be other features as well you may want to turn off but that's one causing your current issue.