fixeria has submitted this change. (
https://gerrit.osmocom.org/c/osmo-pcap/+/42835?usp=email )
Change subject: doc: clarify 'pcap snaplen' / 'max-snaplen'
......................................................................
doc: clarify 'pcap snaplen' / 'max-snaplen'
Change-Id: Ic2c82173c12814d61f0ee9f7454b9e5dcb0c13f4
Related: SYS#8099
---
M doc/manuals/chapters/client.adoc
M doc/manuals/chapters/server.adoc
2 files changed, 14 insertions(+), 0 deletions(-)
Approvals:
fixeria: Looks good to me, approved
Jenkins Builder: Verified
diff --git a/doc/manuals/chapters/client.adoc b/doc/manuals/chapters/client.adoc
index 1769b60..979d326 100644
--- a/doc/manuals/chapters/client.adoc
+++ b/doc/manuals/chapters/client.adoc
@@ -49,6 +49,7 @@
pcap device eth2 <3>
pcap filter udp port 23000 <4>
pcap detect-loop 1 <5>
+ pcap snaplen 9000 <6>
----
<1> Prepare records in pcapng format.
<2> The network device from which to obtain a capture.
@@ -57,6 +58,13 @@
<5> Instruct osmo-pcap-client to automatically add a filter that prevents
capturing the traffic between osmo-pcap-client and osmo-pcap-server,
which would create a loop.
+<6> Maximum number of bytes captured per packet (snapshot length).
+
+Packets longer than the configured `snaplen` are captured truncated, and
+osmo-pcap-client logs an error for each such packet. Note that kernel receive
+offloading (GRO/LRO) can hand libpcap coalesced "super-frames" much larger
+than the link MTU; either raise `snaplen` accordingly or disable offloading on
+the captured interface (e.g. `ethtool -K <iface> gro off lro off`).
Adding or removing new recording network devices during operation is not really
supported, and a restart of osmo-pcap-client is expected for the new
diff --git a/doc/manuals/chapters/server.adoc b/doc/manuals/chapters/server.adoc
index e0d9ff4..5d6ed32 100644
--- a/doc/manuals/chapters/server.adoc
+++ b/doc/manuals/chapters/server.adoc
@@ -46,6 +46,12 @@
<3> TCP port number to which to bind/listen
<4> maximum pcap snapshot length (per packet, in bytes; default: 9000)
+The `max-snaplen` value acts as an upper bound (ceiling) for all connected
+clients: a client is accepted as long as its own configured `snaplen` does not
+exceed the server's `max-snaplen`. It is therefore perfectly fine to configure
a
+larger `max-snaplen` on the server than the `snaplen` used by some clients;
each
+client's trace is recorded using that client's own snaplen.
+
The received packets are stored to a pcap file below the `base-path` using a
filename
encoding both the client name and the date/time at time of file creation.
--
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Gerrit-MessageType: merged
Gerrit-Project: osmo-pcap
Gerrit-Branch: master
Gerrit-Change-Id: Ic2c82173c12814d61f0ee9f7454b9e5dcb0c13f4
Gerrit-Change-Number: 42835
Gerrit-PatchSet: 2
Gerrit-Owner: fixeria <[email protected]>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: fixeria <[email protected]>
Gerrit-Reviewer: laforge <[email protected]>
Gerrit-CC: pespin <[email protected]>
