Bug 1441597
| Summary: | tcpdump: tcpdump can not dump all packets. | |||
|---|---|---|---|---|
| Product: | Red Hat Enterprise Linux 7 | Reporter: | xmu | |
| Component: | tcpdump | Assignee: | Martin Sehnoutka <msehnout> | |
| Status: | CLOSED ERRATA | QA Contact: | Jaroslav Aster <jaster> | |
| Severity: | high | Docs Contact: | ||
| Priority: | urgent | |||
| Version: | 7.4 | CC: | jaster, jiji, msekleta, network-qe, omoris, thozza, xmu | |
| Target Milestone: | rc | Keywords: | Regression | |
| Target Release: | --- | |||
| Hardware: | Unspecified | |||
| OS: | Unspecified | |||
| Whiteboard: | ||||
| Fixed In Version: | tcpdump-4.9.0-5.el7 | Doc Type: | If docs needed, set a value | |
| Doc Text: | Story Points: | --- | ||
| Clone Of: | ||||
| : | 1444755 (view as bug list) | Environment: | ||
| Last Closed: | 2017-08-01 12:13:36 UTC | Type: | Bug | |
| Regression: | --- | Mount Type: | --- | |
| Documentation: | --- | CRM: | ||
| Verified Versions: | Category: | --- | ||
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | ||
| Cloudforms Team: | --- | Target Upstream Version: | ||
| Embargoed: | ||||
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Description
xmu
2017-04-12 09:58:47 UTC
The new version of tcpdump uses bigger snaplen by default, this is probably the root cause of this bug. Compare: Version 4.5.1: # tcpdump -i eth0 port 55555 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes ... Version 4.9.0: # tcpdump -n -i eth0 port 55555 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes ... Notice the difference in "capture size". When running with previously default snaplen it works just fine: # tcpdump -s 65535 -i eth0 port 55555 > /dev/null tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes ^C8 packets captured 8 packets received by filter 0 packets dropped by kernel It also works fine when using bigger capture buffer (-B), no name resolution (-n) or writing to file (-w), so I guess that the name resolution process takes too long and the capture buffer is meanwhile overflowed. Also when you run the nc communication twice, it is captured fine the second time: # tcpdump -i eth0 port 55555 > /dev/null tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes ^C15 packets captured 16 packets received by filter 1 packet dropped by kernel To sum up, I think this is a configuration issue not a bug, but if you want to make this work by default, we can reduce the snaplen size to its previous value. Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2017:1871 |