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I'd be happy to get rid of it if it is indeed out-dated as you say, though that was not my impression. Could you give me some references giving information abou

by Jonhoo 11y ago

I'd be happy to get rid of it if it is indeed out-dated as you say, though that was not my impression. Could you give me some references giving information about how core Internet is now being done?

dvanduzer 11y ago
Plenty of people will still talk about providers that way, but it has never been about topology the way you describe. BGP is a mesh, not a tree. Packets that do have to leave one network are routed to the closest BGP peer. Plenty of small providers peer directly with other small providers (and always have). It's also quite misleading to talk about the hostname once you've mentioned BGP. At that layer, the routers have completely "forgotten" the hostname, and are only looking at IP address/prefix to move that packet. I understand why one might want to illustrate the fact that mail delivered via the SMTP protocol might be retrieved from the same server via the HTTP protocol running in different ports. But this is not a feature of TCP. The term "TCP multiplexing" commonly refers to reusing the same end-to-end TCP session for multiple application requests (e.g. more than one HTTP GET to the same server/port). Very different than IP multiplexing. But email is also a very bad example to use to illustrate IP multiplexing, because email uses a store-and-forward mechanism very unlike HTTP lookups. A sender's email client just doesn't do lookups for a remote email provider. A mail client has a provider-specified SMTP server for all outbound mail traffic, regardless of destination. The client does use DNS to find that server's IP address. But the sender's provider's outbound email server performs an entirely different category of DNS lookup to figure out the destination mail server for the domain. This difference makes it a particularly bad idea to mention SMTP at all, only to say that it's unimportant. I'm sorry this is such harsh criticism. It is extremely difficult to learn this material, let alone teach it to someone else in a digestible fashion. So please don't let this discourage you from trying to write a document like this. But it would be a lot more effective if you just didn't try at all to explain quite so much material in one post. Hope that helps a little?
- Jonhoo 11y ago
  I never refer to it as a tree, only as, effectively, a tiered mesh. While it's true that this breaks down with multi-hop BGP forwarding, I think it conveys enough about how the routing works for a layperson to understand that is relatively close to the truth, no? I could potentially cut down the section on Internet routing significantly, and simply mention that it is a routing fabric that does relatively greedy hop-by-hop forwarding, though I'm not sure that will be more digestable. You're right that BGP doesn't care about hostnames, or even individual IPs, but I'm not sure that distinction is actually relevant to someone who is being exposed to this just now. No, I disagree. IP has no multiplexing features beyond protocol multiplexing. Port numbers that allow multiplexing a single IP among multiple applications on the same host only appear in UDP/TCP. What you are referring to is specifically called HTTP multiplexing, and has little to do with TCP. Again, technically, you are right, however there is nothing in SMTP that precludes the sender from contacting the destination SMTP server directly (well, except that spam detection systems will freak out). The fact that SMTP supports hop-by-hop forwarding, and in many cases this is the only mode that is used, does not mean that this is necessitated by the protocol. And in the interest of making the content easier to understand, I decided describing multi-hop SMTP was simply unnecessary. I appreciate the feedback --- it's always hard to piece together relatively complex posts like this. As I mentioned elsewhere, I specifically wanted this to be a single post such that readers could follow the communication flow end-to-end. I believe this will improve reader comprehension, though of course YMMV.
  - empath75 11y ago
    If I were writing an introduction to lay people, I'd probably just explain the process of loading facebook.com, something people will be very familiar with. Set up a very simple home network topology. A router/modem, and a wired ethernet connection to a laptop. Explain all 4 layers of the tcp/ip model. Explain DNS. BGP seems sort of advanced for an introduction to the topic, to be honest, and so few people use smtp rather than just using gmail's web interface, that it's rather obscure.

by Jonhoo 11y ago

I'd be happy to get rid of it if it is indeed out-dated as you say, though that was not my impression. Could you give me some references giving information about how core Internet is now being done?

dvanduzer 11y ago

Plenty of people will still talk about providers that way, but it has never been about topology the way you describe. BGP is a mesh, not a tree. Packets that do have to leave one network are routed to the closest BGP peer. Plenty of small providers peer directly with other small providers (and always have). It's also quite misleading to talk about the hostname once you've mentioned BGP. At that layer, the routers have completely "forgotten" the hostname, and are only looking at IP address/prefix to move that packet. I understand why one might want to illustrate the fact that mail delivered via the SMTP protocol might be retrieved from the same server via the HTTP protocol running in different ports. But this is not a feature of TCP. The term "TCP multiplexing" commonly refers to reusing the same end-to-end TCP session for multiple application requests (e.g. more than one HTTP GET to the same server/port). Very different than IP multiplexing. But email is also a very bad example to use to illustrate IP multiplexing, because email uses a store-and-forward mechanism very unlike HTTP lookups. A sender's email client just doesn't do lookups for a remote email provider. A mail client has a provider-specified SMTP server for all outbound mail traffic, regardless of destination. The client does use DNS to find that server's IP address. But the sender's provider's outbound email server performs an entirely different category of DNS lookup to figure out the destination mail server for the domain. This difference makes it a particularly bad idea to mention SMTP at all, only to say that it's unimportant. I'm sorry this is such harsh criticism. It is extremely difficult to learn this material, let alone teach it to someone else in a digestible fashion. So please don't let this discourage you from trying to write a document like this. But it would be a lot more effective if you just didn't try at all to explain quite so much material in one post. Hope that helps a little?

Jonhoo 11y ago
I never refer to it as a tree, only as, effectively, a tiered mesh. While it's true that this breaks down with multi-hop BGP forwarding, I think it conveys enough about how the routing works for a layperson to understand that is relatively close to the truth, no? I could potentially cut down the section on Internet routing significantly, and simply mention that it is a routing fabric that does relatively greedy hop-by-hop forwarding, though I'm not sure that will be more digestable. You're right that BGP doesn't care about hostnames, or even individual IPs, but I'm not sure that distinction is actually relevant to someone who is being exposed to this just now. No, I disagree. IP has no multiplexing features beyond protocol multiplexing. Port numbers that allow multiplexing a single IP among multiple applications on the same host only appear in UDP/TCP. What you are referring to is specifically called HTTP multiplexing, and has little to do with TCP. Again, technically, you are right, however there is nothing in SMTP that precludes the sender from contacting the destination SMTP server directly (well, except that spam detection systems will freak out). The fact that SMTP supports hop-by-hop forwarding, and in many cases this is the only mode that is used, does not mean that this is necessitated by the protocol. And in the interest of making the content easier to understand, I decided describing multi-hop SMTP was simply unnecessary. I appreciate the feedback --- it's always hard to piece together relatively complex posts like this. As I mentioned elsewhere, I specifically wanted this to be a single post such that readers could follow the communication flow end-to-end. I believe this will improve reader comprehension, though of course YMMV.
- empath75 11y ago
  If I were writing an introduction to lay people, I'd probably just explain the process of loading facebook.com, something people will be very familiar with. Set up a very simple home network topology. A router/modem, and a wired ethernet connection to a laptop. Explain all 4 layers of the tcp/ip model. Explain DNS. BGP seems sort of advanced for an introduction to the topic, to be honest, and so few people use smtp rather than just using gmail's web interface, that it's rather obscure.