tcpdump mailing list archives
Re: Capturing external packets sent to loopback (FreeBSD) ?
From: Ray Bellis via tcpdump-workers <tcpdump-workers () lists tcpdump org>
Date: Mon, 24 Feb 2020 12:52:52 -0500 (EST)
--- Begin Message --- From: Ray Bellis <ray () bellis me uk>
Date: Mon, 24 Feb 2020 17:53:43 +0000
On 24/02/2020 17:42, Guy Harris wrote:What do you mean by "loopback" here? The term "loopback interface" generally means "fake interface that sends packets from the machine to itself" on UN*Xes, e.g. the lo0 interface on most UN*Xes or just lo on Linux. Is that the type of interface on which you're capturing?It is, but it's also the type of interface typically used when you want to announce a (potentially multi-homed) service address (e.g. via an IGP) that is not directly on a physical interface....why would packets be delivered on the loopback interface if they arrived on a physical interface?That depends on what you mean by "delivered". The daemon is only listening on that single IP address, which is itself only present on the loopback address. The kernel even has a routing table entry for that address, with the correct loopback interface specified as the destination. What appears to be missing is any way to tell the kernel to send a packet that's in transit between the outside and that virtual "inside" interface out to the BPF system. You *can* sniff packets that a machine "sends to itself", though. cheers, Ray
--- End Message ---
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Current thread:
- Capturing external packets sent to loopback (FreeBSD) ? Ray Bellis via tcpdump-workers (Feb 24)
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- Re: Capturing external packets sent to loopback (FreeBSD) ? Ray Bellis via tcpdump-workers (Feb 24)
- Re: Capturing external packets sent to loopback (FreeBSD) ? Guy Harris via tcpdump-workers (Feb 24)
- Re: Capturing external packets sent to loopback (FreeBSD) ? Ray Bellis via tcpdump-workers (Feb 24)
- Message not available
- Message not available
- Re: Capturing external packets sent to loopback (FreeBSD) ? Ray Bellis via tcpdump-workers (Feb 24)
- Re: Capturing external packets sent to loopback (FreeBSD) ? Guy Harris via tcpdump-workers (Feb 24)