What

Earlier in this track, you learned that all CF HTTP Routes resolve to the IP of the HTTP load balancer and that all TCP Routes resolve to the IP of the TCP Load balancer.

But if all routes resolve to the IP of a load balancer, then how does traffic actually get sent to an application????

Well, it depends if the route is HTTP or TCP.

One major difference between the HTTP protocol and the TCP protocol, is that HTTP packets contain more headers. These headers can carry all sorts of information, including what URL the request is being made to. (The client can even set arbitrary headers themselves!) GoRouter is able to look at this headers, see the requested URL, and route appropriately based on the information in the Routes Table. Because of this, all HTTP routes can have identical route ports (80 or 443).

gorouter routing

TCP is barebones. TCP packets have very limited headers that only include the source and destination ports of the packets. Because of this, the TCP Router has no knowledge of the URL. So the TCP Router needs something else to differentiate between apps. It can’t be the destination IP because all TCP routes have the same destination IP. The only thing left, is the destination port. Because of this, all TCP routes must have unique route ports.

tcp router routing

How

📝 Inspect HTTP headers

  1. Curl the networking api and look at the request headers 
    cf curl /networking/v1/external/policies -v

    You should get a response that looks like this:

    REQUEST: [2019-04-24T11:01:49-07:00]
GET /networking/v1/external/policies <---- this is the header that contains the URL path
HTTP/1.1
Host: api.beanie.c2c.cf-app.com      <---- this is the header that contains the URL base
Accept: application/json
Authorization: [PRIVATE DATA HIDDEN]
Content-Type: application/json
User-Agent: go-cli 6.43.0+815ea2f3d.2019-02-20 / darwin

❓ Question

What would happen if two TCP routes had the same route port?

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