Bug ID 594064: tcpdump with :p misses first few packets on forwarding (UDP, FastL4) flows.

Last Modified: Oct 16, 2023

Affected Product(s):
BIG-IP LTM(all modules)

Known Affected Versions:
11.2.1, 11.3.0, 11.4.0, 11.4.1, 11.5.0, 11.5.1, 11.5.2, 11.5.3, 11.5.4, 11.5.5, 11.5.6, 11.5.7, 11.5.8, 11.5.9, 11.5.10, 11.6.0, 11.6.1, 11.6.2, 11.6.3, 11.6.3.1, 11.6.3.2, 11.6.3.3, 11.6.3.4, 11.6.4, 11.6.5, 11.6.5.1, 11.6.5.2, 12.0.0, 12.0.0 HF1, 12.1.0 HF1, 12.0.0 HF2, 12.1.0 HF2, 12.0.0 HF3, 12.0.0 HF4, 12.1.1 HF1, 12.1.1 HF2, 12.1.2 HF1, 12.1.2 HF2, 12.1.0, 12.1.1, 12.1.2, 12.1.3, 12.1.3.1, 12.1.3.2, 12.1.3.3, 12.1.3.4, 12.1.3.5, 12.1.3.6, 12.1.3.7, 12.1.4, 12.1.4.1, 12.1.5, 12.1.5.1, 13.0.0, 13.0.0 HF1, 13.0.0 HF2, 13.0.0 HF3, 13.0.1, 13.1.0, 13.1.0.1, 13.1.0.2, 13.1.0.3, 13.1.0.4, 13.1.0.5, 13.1.0.6, 13.1.0.7, 13.1.0.8, 13.1.1, 13.1.1.2, 13.1.1.3, 13.1.1.4, 13.1.1.5, 13.1.3, 13.1.3.1, 13.1.3.2, 13.1.3.3, 14.0.0, 14.0.0.1, 14.0.0.2, 14.0.0.3, 14.0.0.4, 14.0.0.5, 14.0.1, 14.0.1.1

Fixed In:
14.1.0, 13.1.3.4, 12.1.5.2, 11.6.5.3

Opened: May 18, 2016

Severity: 4-Minor

Related Article: K57004151

Symptoms

When the tcpdump utility is used with the ':p' modifier, it appears that the first few serverside packets are not captured.

Impact

Typically, the peer flow will not be captured until the second packet is processed on the original flow that is captured by the tcpdump filter. Although there is no operational impact, it might cause confusion when looking for serverside traffic when capturing using a command similar to the following: tcpdump -i <vlan>:p host <client-ip> Typical examples of missing packets include: -- Serverside syn and syn-ack from FastL4 TCP traffic. -- All serverside packets for single packet request/reply traffic, e.g., dns request/reply.

Conditions

-- Using the ':p' modifier with the tcpdump utility to capture serverside flows associated with clientside flows that match a tcpdump filter. -- FastL4 or standard virtual server UDP flows are being captured.

Workaround

Specify filter that includes serverside traffic (e.g., include pool member addresses as 'host <addr>').

Fix Information

tcpdump now successfully captures the first serverside packets.

Behavior Change

Guides & references

K10134038: F5 Bug Tracker Filter Names and Tips