How are packets routed based on IP and how are those routes acquired?

Question

Good day all,

this is my first question here, be gentle in judgement

Background:

At university, we are covering Network Routing Protocols. Having possibly found 2 issues with current routing protocols, I believe I have a improved solution for routing information to be acquired.

Question:

Since DNS server's purpose is to store "names" which correspond to server IP's, thus resolving the DNS name to an IP, how are IP's resolved to their specific node/device.

More Info:

We take for granted the fact that the IP 8.8.8.8 will reach Google's DNS server, but how is this actually routed. What routing information will my node/laptop contain for it to be able to send a TCP/ICMP packet to 8.8.8.8.

Does the gateway (my router) determine this, does my exchange/DSLam determine this or the ISP.

In my case, my Linux distro routes all traffic to the lowest route which is my router. The router will route all traffic to the exchange, from there going to the ISP, from here, how does it reach 8.8.8.8

TL;DR

How does a packet specified by an IP 8.8.8.8 get routed to the device with the corresponding IP, and how are those "routers" routing information acquired?

Answer 1

Routers learn about routes in three ways:

• Directly connected networks
• Manually configured static routes
• Dynamically through routing protocols

A router, receiving a packet on an interface will look at the destination address of the packet, and it will look in its routing table to see if it knows how to forward the packet toward its destination.

If the router doesn't find any sort of match in its routing table, it will discard the packet.

If the router finds a match, even if it is only a default route, it will forward the packet out the new interface toward its destination. The interface towards the packet destination can be connected to another router, and the new router will repeat what the first router did. This router lookup and forward goes on until the packet gets to the network where the destination host is.

Answer 2

Google advertise routes to the network block 8.8.8.0/24 over BGP to other networks they connect to. These networks will pass on these route advertisement subject to commercial policies.

Typically a network will have three main types of interconnection. Transit providers who sell them service. Transit customers who buy service from them and peers.

A route recieved from a customer will generally be passed on to customers, providers and peers. A route received from a provider or peer will normally only be passed on to customers.

Routes will only generally be passed on if they are considered the best route to a prefix. What exactly "best" means is dependent on local policy.

Networks making up the Internet are represented by "AS Numbers". With each AS the route passes through different networks an "AS Path" is built up. This is used to block loops and also in the absense of local rules to the contary is used to dermine the best path.

When it comes to actually forwarding the packets longer prefixes win over shorter ones (so a route to 8.8.8.0/24 would win over one to 8.8.0.0/16 )

In the "edge" parts of your ISPs network the packet will likely be carried by default routes towards your ISPs core. There is little reason to import the complete internet routing table on such devices.

Within your ISP's core (or for very small ISPs possiblly an upstream provider) there will be routers with a massive routing table covering the whole Internet built up from the routes they have received from other networks. Right now the routing table for the IPv4 Internet has about half a million routes. This table will route the traffic towards Google.

When the packet reaches google they will need to route it internally towards one fo theier DNS servers (8.8.8.8 is NOT a single machine). Some operators use a specific internal routing protocol for this, some use BGP internally as well as externally, some may use manual routes. I'm not sure what google does.

Answer 3

When packet reaches layer3 devices ,layer3 device will forward packet towards destination by checking routing table ,based on routing table packet is forwarded to next hop . Basically routing table is framed with manual configuration static ,and dynamic routes and by directly connected networks

If the packet won't find the route towards the destination in routing able packet will get discarded .