Table Of Contents
Table Of Contents

Step 25. PCAP recording

Goals

The goal of this step is to demonstrate PCAP recording capabilities for capturing OSPF traffic.

INET’s PCAP recorder module can capture network traffic at specific interfaces and save it in PCAP format, which can later be analyzed with tools like Wireshark. This is useful for:

  • Debugging OSPF protocol issues

  • Understanding packet-level protocol behavior

  • Verifying LSA contents and exchanges

  • Analyzing timing and sequencing of OSPF messages

Configuration

This configuration is based on Step 1. PCAP recorders are configured on specific interfaces of selected routers.

../../../_images/OspfNetwork.png

The configuration in omnetpp.ini is the following:

[Config Step25]
description = "PCAP recording"
extends = Step1

**.crcMode = "computed"
**.fcsMode = "computed"

*.R1.numPcapRecorders = 1
*.R1.pcapRecorder[0].moduleNamePatterns = "ppp[0]"
*.R1.pcapRecorder[0].pcapNetwork = 204        # ppp
*.R1.pcapRecorder[0].pcapFile = "results/R1.ppp0.pcap"

*.R5.numPcapRecorders = 1
*.R5.pcapRecorder[0].moduleNamePatterns = "ppp[1]"
*.R5.pcapRecorder[0].pcapNetwork = 204        # ppp
*.R5.pcapRecorder[0].pcapFile = "results/R5.ppp1.pcap"

*.R4.numPcapRecorders = 1
*.R4.pcapRecorder[0].moduleNamePatterns = "eth[0]"
*.R4.pcapRecorder[0].pcapNetwork = 1        # ethernet
*.R4.pcapRecorder[0].pcapFile = "results/R4.eth0.pcap"

Results

With PCAP recording enabled:

  1. PCAP recorder modules capture all traffic on the specified interfaces.

  2. Separate PCAP files are created for each configured interface:

    • R1.ppp0.pcap - Traffic on R1’s ppp0 interface

    • R5.ppp1.pcap - Traffic on R5’s ppp1 interface

    • R4.eth0.pcap - Traffic on R4’s eth0 interface

  3. These PCAP files can be opened in Wireshark to examine:

    • OSPF Hello packets

    • Database Description (DBD) packets

    • Link State Request/Update/Acknowledgment packets

    • LSA contents (Router LSAs, Network LSAs, Summary LSAs, etc.)

  4. The PCAP files show the timing and sequencing of OSPF protocol messages, useful for understanding adjacency formation, LSDB synchronization, and LSA flooding.

PCAP recording is a powerful tool for learning OSPF protocol details and troubleshooting complex scenarios.

Sources: omnetpp.ini, OspfNetwork.ned

Discussion

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Step 24. OSPF Path Selection - Suboptimal routes
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