how to instert "x-forwarded-for" data to http header in physical l4 switch?

daniel

8/30/23, 8:02 PM

In the L4 switch, there is an 'x-forwarded-for' function that puts the client source ip address in the http header.

The l4 switch can only know layer 4 information, so I'm curious how to put the x-forwarded-for information http header(http header is in the layer 7!! ). Even in https, the http header is encrypted, how can L4 switch decrypt this encrypted http header, insert x-forwared-for information, and send a packet to the backend?

Thanks!

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switch

x-forwarded-for

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Server

John Mahowald

9/4/23, 1:12 AM

No, a layer 4 only device cannot mangle layer 7 application data.

A layer 4 host might be a router that can forward for example 2001:db8:e856:edff::a0f8 to 2606:2800:220:1:248:1893:25c8:1946. Perhaps it has enough transport layer knowledge to have a firewall rule allow this for tcp/443. But it does not know how to unwrap packets further and manipulate http headers.

Commonly designs have a load balancer or other middleware that redirects or modifies application data. This is where it makes sense to put a frontend service address, terminate TLS, transform the request, and proxy a new request to a backend. Because it is a new request, client IP is lost, which is why Forwarded headers were invented in the first place. Doing all this requires application knowledge, so such a host has level 7 functions.

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Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: how to instert "x-forwarded-for" data to http header in physical l4 switch?

TH: จะแทรกข้อมูล "x-forwarded-for" ไปยังส่วนหัว http ในสวิตช์ l4 จริงได้อย่างไร

RO: cum se introduc datele „x-forwarded-for” în antetul http în comutatorul fizic l4?

RU: как вставить данные «x-forwarded-for» в заголовок http на физическом коммутаторе l4?

VI: làm cách nào để chèn dữ liệu "x-forwarded-for" vào tiêu đề http trong chuyển đổi l4 vật lý?

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