Outbound and Inbound traffic in BGP

[misaleh]

I'm confused about something and I'd like your help in understanding. Where I work, we have a router that's connected to 2 ISPs via BGP. Weight is set to 100 to ISP-A and 50 to ISP-B so outbound traffic is going through ISP-A and AS-Path prepend is modified so inbound traffic is going through ISP-B. What I'm confused about is, what kind of traffic goes through ISP-A and what kind of traffic through ISP-B? Like if a client is downloading, uploading, or browsing, traffic goes through A or B? Thanks in advance.

[MHM Cisco World]

Downloading' the traffic is from ISP-B

Uploading' the traffic is to ISP-A 

MHM

[Joseph W. Doherty]

I'm confused by your question.

You describe ingress and egress flows, per ISP and ask what kind of traffic flows through the ISPs.  From your description it should be all kinds.

In other words, I'm confused because you appear to answer your own question.

Could you elaborate on your confusion?

[misaleh]

If a client is downloading a file from a website, does the traffic go through ISP-A or B? Similarly, if a client is uploading a file or browsing a website or like doing a speed test.

[Joseph W. Doherty]

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@misaleh wrote:

If a client is downloading a file from a website, does the traffic go through ISP-A or B? Similarly, if a client is uploading a file or browsing a website or like doing a speed test.

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From what you've described, for those examples, there would be two way traffic flows, "up" would transit one ISP and "down" would transit other ISP.  This would be an example of asymmetric routing.

Asymmetric routing is a situation where packets take one path to go from the source to the destination, but replies take a different path to return. This is not always a problem, but it can become an issue when there is something stateful in the path, such as a NAT device or a firewall.

In such cases, the return network traffic takes a different path from the original outgoing flow, which can cause problems. For example, in firewalls, state information is built when the packets flow from a higher security domain to a lower security domain. This can lead to issues with connections being dropped or not being established properly.

It’s also possible to have asymmetric routing in configurations where traffic goes out one link to the internet and returns through a different link. This is commonly seen in Layer-3 routed networks and can be caused by issues with route-to or reply-to, both having to do with gateways on interface settings.

[misaleh]

Thanks for replying, but I'm still confused. What kind of traffic is considered "up" and what kind is considered "down"? If ISP-A bandwidth is 100 Mbps and ISP-B is 50 Mbps, which bandwidth is being utilized when downloading, uploading, browsing? Sorry if I seem stupid lol

[bo chen]

The data sent from your local area to the carrier is called uplink traffic, for example, when you transfer photos from your computer to a cloud storage device. On the contrary, the traffic sent to you from the operator is called downlink traffic. For example, downloading files.
I hope my answer can be helpful to you.

[MHM Cisco World]

this lab for you 
I make ISP prefer path to 1.1.1.1 via Edge2 by as-prepend 
and make Core select the path to Edge1 for 5.5.5.5 
and this what you get 
I ping from Core to ISP LO
the ping request pass via edge1 
the ping reply pass via edge2 
and it same for upload and download 

MHM

[Joseph W. Doherty]

"up" and "down" is considered toward the "core" of the network.  In this case up/to and down/from Internet.  Traffic kind/type doesn't matter, only traffic's direction.

Regarding bandwidth, that would be whatever is provided along a particular path.  From what you describe, that would be 100 Mbps using ISP-A and 50 Mbps using ISP-B.  However, do note, ISP bandwidth might vary, for that particular ISP based on "up" and "down".

BTW, no you don't seem stupid if learning networking, but you may be looking for complexity where there's none.

An an analogy, consider two elevators, side-by-side, one "A" and one "B".  You're on the ground floor and you need to exchange mail with the top floor.  You take elevator "A" up and elevator "B" down.  Oh, and perhaps one elevator is a passenger elevator and the other a freight elevator, i.e. they move at different speeds.

[misaleh]

So if I understand correctly, based on what you've said, then if a client is uploading a file, it will be sent via the link to ISP-A which is 100 Mbps (upload speed could be less) and if a client is downloading/browsing then that will go through the link to ISP-A and then from the internet it will return via ISP-B which is 50 Mbps. Did I understand correctly?

[MHM Cisco World]

Will test tcp traffic in my lab to end confuse here. 

MHM

[Joseph W. Doherty]

"Upload you have servers in your network abd client outside access to it."

BTW, from those clients perspective, they would be downloading.

[MHM Cisco World]

Sure of he have server inside and client outside he will use upload for server but for outside clients it download. 

But for download and he run any tcp I need to check.

MHM

[Joseph W. Doherty]

Correct, although even in the file upload case, likely something like TCP ACKs would be returning via ISP-B.  Remember most traffic conversations compromise two way traffic.

[Richard Burts]

up and down roughly correspond to outbound and inbound. Let me explain it this way:

If a user is sending a file to someone then the user device sends a frame using ISP-A, the acknowledgment of that frame comes back using ISP-B. repeat over again for every frame sent.

If that user is receiving a file from somewhere then the server with the file sends a frame to the user which uses ISP-B and the acknowledgment of the frame goes using ISP-A. repeat over again for every frame sent.

Both bandwidths are used when sending a file. Which one is data and which one is acknowledgement depends on whether the user is sending a file or receiving a file. If the user is sending a file then the data packet uses the 100 Mbps and the acknowledgment uses the 50 Mbps which is fine. If the user is receiving a file then the data packet uses 50 Mbps and the acknowledgment uses 100 Mbps which is less fine. That is now it works.